FORESTRY
Mike Newton
Revised November 19, 2008
Undesirable woody and herbaceous plants are problems in commercial forests and on fencelines and rights-of-way. Safe, dependable methods of chemical weed control have been developed for most forestry needs. Reforestation, in particular, may depend heavily on weed control. Depending on local conditions and weed composition, the results sought differ strikingly in degree of control and composition of residual vegetation and, hence, in the choice of method. The Oregon Forest Practices Act mandates successful reforestation after logging. It also prescribes certain rules regarding herbicide use to protect plantations and water. Operators should be familiar with these rules and labels whenever herbicides are used.
Forest Land Brush Control
The objective of weed or brush control in commercial forests is to provide larger, higher quality harvests and to reduce the time required to bring the crop to maturity. Objectives also include protection of wildlife habitat and water quality. Research in the past 20 yr has made very clear that virtually no other practice will produce as much gain in plantation performance as reducing competing cover, and that careful application of the appropriate chemicals exceeds other methods for most operations in safety and habitat protection. 
Weed control alone cannot produce a harvest; it must be combined with cultural practices involving either seeding or planting and with practices that bring the crop to maturity. Growing trees is the ultimate objective, not killing brush; brush/weed control is merely a phase of the reforestation procedure. Selective vegetation control also is an efficient method of enhancing certain kinds of wildlife habitat. Much of the early forest vegetation control work with herbicides was directed toward wildlife enhancement, and probably no set of tools is as capable of providing improved wildlife forage and long-term habitat development as a well-thought-out vegetation management program relying primarily on herbicides.
Weed control enhances conifer survival and growth on all potentially productive sites. On harsh sites in southwestern Oregon, almost total weed control is essential even to obtain survival, and it may be necessary to maintain a weed-free site for more than 2 yr. On better sites in the Coast Range, although initially weeding may not be essential for survival, fast-growing herbs and brush will threaten survival in a few years, and treatment to avoid brush problems will enhance productivity greatly. Indeed, weeding pays best on the best sites, even though the percentage increase is greatest in poorer sites.
Chemicals
Virtually all brush and weed-tree control in forests is with 2,4-D, glyphosate, imazapyr, picloram, or triclopyr; situations determine whether these herbicides are applied as spring or fall dormant or foliage sprays of diluted concentrates. Injections or cut-surface applications rely on high concentrations, including undiluted concentrates. Atrazine, 2,4-D, sulfometuron, and hexazinone are used to control herbaceous weeds in plantations, nearly always in spring. Clopyralid is very versatile in controlling thistles and other composite and leguminous weeds during active growth, when most other herbicides will damage conifers. Fluroxypyr is registered for selective brush control in pine plantations. These materials, singly or in combination, give broad-spectrum activity on forest species, in many cases selectively favoring desirable conifers. Triclopyr and 2,4-D can be used selectively (but avoid high rates; see label) over Douglas-fir seedlings during the dormant seasons but will injure ponderosa pine and noble fir. Glyphosate and imazapyr can be used selectively to favor conifers only in late summer or early fall. Picloram and metsulfuron  nearly always harm conifers when applied directly; use them for site preparation only. Satisfactory reforestation brush control can be achieved with the proper formulation of these compounds applied at the proper season and with the right carrier. 
Soil-active herbicides that are effective on brush are seldom suited for selective control in this region because of their tendency to injure conifers; they are useful for site preparation and are highly effective when applied before timber harvest to prevent postharvest sprout growth. Glyphosate is highly effective only on deciduous and herbaceous species. In fall, glyphosate will selectively remove brush and herbs from conifers. In midsummer, glyphosate damages conifers and brush severely. Imazapyr is active on maple, alder, and other brush as a growth inhibitor. At high rates, it also might inhibit conifers. Imazapyr is well adapted for trunk injection or spot treatments. Triclopyr is registered for site preparation and release, and it may be injected as the amine salt. Picloram (when not mixed with other products) is useful only in site preparation and trunk injection. Picloram is a restricted-use product because of its mobility; use it with this in mind. Note restrictions on the label when grazing treated areas.
Two sulfonylurea products, metsulfuron and sulfometuron, are registered for use in forestry. They are used at rates much lower than for most other products. Both are somewhat persistent in soil. Metsulfuron is useful at present only for site preparation. Take care to avoid using sulfometuron at the upper range of registered rates unless you can wait several months between spraying and planting. Until more is known about the residues, metsulfuron should be considered safe only in moderately high rainfall areas and when trees are planted at least 6 mo after treatment. Principal target weeds for metsulfuron are the Rubus species and ferns. Sulfometuron is used for grass, fern, and general herb control in reforestation areas. Neither of these sulfonylurea products controls thistles, and so may need to be tank-mixed with hexazinone, clopyralid, or 2,4-D. Both sulfonylurea products are extremely effective on a number of hard-to-kill species, but use them with care to avoid overdosage. Mixing with other chemicals is often recommended to enhance control of thistles and other weeds on which these products may be weak. Some of the above products registered only for site preparation may have future uses for conifer release. Check current labeling before purchasing. A new chemical, aminopyralid, is registered for use to control broadleaf weeds and some brush in forests or on forest roadsides (noncrop) use. The product with aminopyralid alone, Milestone VM, is permitted only on roadsides, whereas the combination of aminopyralid and triclopyr amine is permitted for use in forests for site preparation, directed spray and cut surface applications (see the label for specific uses). Selectivity is not specified, and broadcast application over conifers is not permitted at this time.
Nonchemical Methods
Some weeds lend themselves reasonably well to removal without chemicals. Alder more than 2 inches in diameter can be killed fairly well by cutting at the ground line from mid-June to mid-August. Smaller stems are more likely to sprout at any time. Fungi complement the cutting to kill stumps. Alders cut at other times are likely to sprout vigorously. Most other western Oregon and Washington hardwoods sprout if cut at any time. Applying water-soluble concentrates of 2,4-D amine, triclopyr amine, glyphosate, or imazapyr to freshly cut (less than 20 minutes) stumps keeps sprouting to a minimum unless hardwoods are cut between December and May.
Grazing intensively can in some circumstances remove palatable herbs and many brush species. Great care is required when grazing among conifers to keep animals out of plantations when trees are actively growing. Grazing is among the most difficult methods of control because weed removal must be relatively complete to provide significant benefits, and this degree of control is difficult to achieve without animal damage to trees. However, intensive pasturing of a cut-over hardwood stand for the 2 yr immediately after logging will remove many of the sprouting brush species and may help simplify the weeding job to herb removal only. However, herbs may recover too quickly for this procedure to do the whole job of site preparation. The need to reduce cover to very low levels means the livestock will not gain weight well in programs such as this. If they are not grazed to this intensity, some supplemental weeding will be necessary, either with paper mulch or chemicals. Do not attempt to mulch while grazing, for obvious reasons.
Paper mulch has had success comparable to grass herbicides. In southwestern Oregon and near the Willamette Valley of Oregon, mulch paper should be at least 9 sq ft (3 ft x 3 ft). On coastal areas and in western Washington, 4 sq ft (2 ft x 2 ft) should be adequate. Mulch paper should be fiber-reinforced laminated Kraft paper with an asphalt core for adequate durability. Mulch paper must be well weighted on all four corners or pinned to the ground. Clear plastic will not work. Black plastic will work and is lightweight but difficult to handle.
Mechanical tillage  Using heavy equipment to till forest soil has limited value on cutover land because of stumps, logs, and other obstacles. Recent trials of large subsoil or ripping equipment have shown promise on compacted soil and clayey soils with restricted drainage, leading to easier planting and better root development. The procedure is not a truly effective weed control measure, however, and usually should be preceded or followed by a chemical application to postpone weed development.
Most serious forest weeds are not controlled as well with nonchemical techniques as they are with herbicides. Sprouting is difficult to control without repeated cutting. Most evidence to date clearly points to the need to kill root systems to minimize competition. For growers whose goal is vigorous tree growth and minimum impact on soil and labor force, no alternatives to herbicides have been proven to be as safe or as effective. 
Vegetation Control with Herbicides
The methods selected to apply herbicides for brush control depend on the species composition, proximity of crops, degree of control required, and available equipment. Method and season of application also have a major influence on degree of selectivity.
In general, large areas of brush in which most stems are less than 2 inches in diameter and grassy weeds that cannot be controlled with farm equipment are best treated by aircraft. Under some circumstances, such as in small units and/or on favorable terrain, broadcast treatment with the waving-wand method is excellent. Spot brush control is best suited for hand or tractor-mounted ground rigs. Weed trees over 1.5 to 2 inches in diameter and conifers to be thinned are most economically treated by injection. Some other methods are useful in special circumstances, but broadcast applications by air or ground rigs usually give the best results per dollar. The commonly used methods are described below, with special emphasis on objectives, formulations, and equipment peculiar to each.
Foliage Application
Foliage spraying is extensively used. Selectivity for conifers at dosages that clear a site of nearly all competitive cover is dependent on season and dosage. Brushfields that are to be converted to conifer stands are best suited to summer foliage spraying before planting. Species such as vine maple (see tables later in this chapter for recommendations) may be satisfactorily controlled by this method but only with highly systemic products such as glyphosate and imazapyr. Manzanita, Ceanothus spp., madrone,  and other persistent-leaved brush species lend themselves to satisfactory control with foliage treatments of growth regulator products (e.g., 2,4-D or triclopyr esters) at any season from late dormancy until late midsummer, but treatments often work best in early spring. 
The choice of season for controlling these species is determined in part by the availability of spray equipment and the presence or absence of susceptible crop trees. Alder and salmonberry are usually injured by foliage sprays. It is important to wait until alder plants have at least two to three leaves for good control with 2,4-D or triclopyr. Check product labels carefully because optimum application times vary. For instance, conifer release works best in the fall when applying glyphosate to control alder, salmonberry, and thimbleberry with glyphosate. The optimum season for control of target species is usually midsummer, but that is also when many conifers are most sensitive. The choice of earlier or later differs among chemicals and between site preparation and conifer release treatments, and if release, which conifers are to be released; e.g., never spray phenoxy herbicides over ponderosa pine in early spring.
Herbicides Aminopyralid, 2,4-D, clopyralid, fluroxypyr, triclopyr, imazapyr, glyphosate, metsulfuron, dicamba, and picloram are the herbicides used for foliage applications. For application rates, see the tables later in this chapter. Glyphosate plus imazapyr gives excellent control of mixed deciduous brush species. Picloram, dicamba and metsulfuron are highly toxic to most conifers when applied directly, but seedlings planted 6 mo or more after treatment normally are unaffected. Water is almost always used as a carrier; in late summer a small amount of a crop oil or diesel fuel (up to 5%) may be added to emulsifiable products including  mixtures containing 2,4-D or triclopyr.
Adjuvants may be added to spray mixtures to enhance foliage activity. However, each commercial herbicide product may or may not have its own emulsifiers and wetting agents. Adjuvants do not always increase efficacy. Most (but not all) surfactants decrease selectivity in conifers. In general, adjuvants are not recommended if conifer selectivity is desired.
Application  The choice of whether to spray foliage from the air or with ground equipment depends on the size of the job and the equipment available. For most small spray jobs, small equipment is most satisfactory. A backpack sprayer with adjustable cone nozzles can apply sprays at 3 to 10 gal/A quite uniformly (waving wand technique) on cover less than 8 ft tall, if the applicator can move relatively freely. Note that most product labels show a minimum of 5 gal/A. This technique is much faster than the spray-to-wet procedure and wastes much less chemical. 
The waving-wand method of application is uniquely suited for treating small clearings and brush beneath a canopy of conifers or hardwoods being prepared for harvest. These low-volume applications have great promise for allowing planting immediately after logging if the preharvest application contains both foliage-active products such as glyphosate/imazapyr and soil-active materials such as sulfometuron. Preharvest treatment prevents perennial species from sprouting, and greatly simplifies postharvest applications by preventing immediate green-up. When using the waving-wand technique for site preparation or release, it’s very important to keep the nozzle pointed above the target vegetation so that the light spray comes down directly on the foliage rather than cross-wise. Foliage is naturally designed to capture light from above, and this orientation also is excellent for catching a light spray. Wearing a hat with visor, gloves, long-sleeve shirt, and rubber boots will minimize the applicator’s exposure. For directions on this technique, read Handbook of Weed and Insect Chemicals for Forest Resource Managers, by M. Newton and F.B. Knight (Timber Press). For broadcast application rates, see recommendations in the following sections of this chapter for boomless nozzles on ground rigs and aerial equipment.
Aerial applications use 5 to 10 gal/A of spray mixture, as described on the label. Ground equipment is very good for small jobs, but the labor required often is excessive on jobs of more than 40 acres, and aerial application may be preferred. On large jobs, aerial spraying is a less expensive way to apply herbicides. 
Herbicide selectivity and species composition  Certain herbicides are effective on different mixtures of brush species and herbs. However, forest weed communities are far more diverse than agricultural fields, so several products may be required in a tank-mix. For example, if a recent cutover has developed a cover of grasses and forbs such as tansy ragwort and thistles—plus vine maple, elderberry, and salmonberry in the draws—a single product will merely change species composition. A site-preparation mixture for such a target group might include sulfometuron, glyphosate, and clopyralid, each at a dosage capable of removing a target species. This may be a costly prescription, but is much less costly than repeated applications, each of which may be inadequate. In tank-mixes, however, each product must not exceed the rate of application given on the label.
Dormant Application
Make dormant applications when conifer buds begin to swell but have not opened. Exclusively water-soluble products generally are not used at this time. Dormant applications are used where Douglas-fir or true firs are established and require release from brush that is susceptible at this season. Unless the brush species retain green foliage during winter, oil is used for the herbicide carrier. Emulsions containing oil may be as effective on the persistent-leaved brush. Pines, especially ponderosa, are sensitive to dormant sprays, particularly those containing oil, after the end of January.  Sprays containing oil now appreciably increase the cost of treatment, leading to decreased reliance on dormant sprays.
Herbicides  Triclopyr esters and 2,4-D are the most frequently used products in dormant applications. They are applied by helicopter in low volumes of oil or water-oil mixtures. Other types of ground apparatus are not well adapted to this type of treatment. There are no known substitutes for oil on certain deciduous brush species and Scotch broom when there are no leaves. Water is appropriate on evergreen brush; adding a surfactant or 5% oil may improve results. Except for vine maple, most species can be treated in summer. Vine maple  is most sensitive to triclopyr in March and April. 
Basal Application
The basal application method is generally used to selectively treat individual woody plants. This method also lengthens the period of time that brush can be sprayed; basal applications are effective from February to November. For basal treatments, mix the spray with oil and apply to the lower 15 inches of a tree trunk or brush stem, soaking the trunk liberally to the ground line. Basal treatments usually control even larger hardwood trees with thick bark. Application is easiest if the base of the tree is scraped bare of moss and debris before treating.
Herbicides  Basal sprays always are applied with oil as a carrier, using either diesel or one of the crop oils now available. Rates are 4 to 20 lb ai of triclopyr ester herbicide (e.g., 1 to 5 gal Garlon 4/Garlon 4 Ultra) to each 100 gal of oil used. For success, the stem must be soaked and thoroughly covered throughout treatment area. Results from basal treatments are not apparent immediately. Often the tree will leaf out and die back 1 or 2 yr before finally dying. Incompletely covering the circumference leads to sprouting, and the entire tree is likely to survive. 
Some applications to young sprouts with highly concentrated triclopyr ester (even undiluted concentrate) have been highly effective on maple stumps and sprouts 2 to 3 yr after cutting. These applications, although effective, use more chemical per unit of effectiveness than more diluted oil solutions. The ester form of triclopyr is most suitable for basal spraying.
Spring applications may produce best top kill, whereas summer and fall sprays may give better sprout control. Winter treatments may require a higher volume of spray with higher concentration as well.
Low-volume Basal Bark Treatment
For susceptible woody plants with stems less than 6 inches in diameter at the base, mix 20 to 30 gal triclopyr ester in enough oil to make 100 gal of spray mixture. Apply with backpack or knapsack sprayer using low pressure and a solid cone or flat fan nozzle. Spray basal parts of brush and tree trunks to thoroughly wet lower stems, including root collar area, but not to the point of runoff. Vary herbicide concentrations with size and susceptibility of species treated. Apply any time, including winter, except when snow or water prevents spraying to the ground line. Avoid treating when bark is soaking wet with water.
Thinline Basal Bark Treatment
To control susceptible woody plants with stem diameters under 6 inches, apply undiluted triclopyr ester product in a thin stream to all sides of lower stems. Direct the stream horizontally to apply a narrow band of herbicide around each stem or clump. From 2 to 15 ml of chemical will be needed to treat single stems and from 25 to 100 ml to treat clumps of stems. Use an applicator metered or calibrated to deliver the small amounts required. A D2 nozzle gives the desired stream. This is effective on sprouts with smooth bark.
Cut-surface Application and Stump Treatment
In the frill treatment, the tree trunk is hacked or frilled at intervals around the trunk at a convenient level. Cuts must be through the bark and into the sapwood; chips remain connected to the tree to form a small cup. The cut frill can be treated any time of year (summer or fall is best), but the cut section should be treated with concentrated amine-formulated herbicide immediately after the frill is made. Few species require complete frilling. Spaced axe cuts with 0.25 tsp—which is about equal to one milliliter (ml) or cubic centimeter (cc) of undiluted water-soluble herbicide product per cut—are usually adequate. Imazapyr may be diluted (1:3) in water to 1 lb/gal for most species other than bigleaf maple, on which 1 lb/gal (1:3 dilution) should be effective in summer, and 2 lb/gal (1:1 dilution) December through April.
Season can be important in cut-surface applications. Certain herbicides, including 2,4-D or triclopyr amines, are most effective during the early summer. Picloram, glyphosate, and imazapyr, are most effective when applied from midsummer to leaf fall. Rising sap in spring dilutes the herbicide and may prevent movement to the roots.
Stumps may be treated with either of two methods. One is the same as for basal treatment except that the top is removed and the stump is treated to prevent regrowth and resprouting. Research with bigleaf maple and Oregon white oak shows results are best if the stump is thoroughly soaked around the ground line and the cut surface with a basal spray solution (triclopyr ester in oil) any time after cutting but preferably before it resprouts. It is far less costly, however, to apply undiluted water-soluble herbicides (the amine form of triclopyr or glyphosate) to only the perimeter of the freshly cut stump surface. A tablespoonful is adequate for almost any stump less than 1 ft in diameter when uniformly distributed in a thin line around the perimeter of the live wood. More is required for stumps over 12 inches in diameter. Stumps thus treated may sprout weakly the second year if treated during the growing season or fall. Spring stump treatment is not as successful. A delay between cutting and treatment of even 1 hour may reduce effectiveness unless esters are used.
Herbicides  Imazapyr, glyphosate, triclopyr amine, or picloram, used singly or in combination, are most effective and easiest to apply in the frill-and-girdle method. Esters do not work as well except if applied to stumps cut 1 to 30 days before treatment. Most chemicals, other than imazapyr, are used undiluted. On hardwoods other than maples, triclopyr amine may be diluted to half strength with water. Triclopyr amine is very effective on many species. Imazapyr may be diluted to quarter-strength and still be effective on most species. Glyphosate may be used at half to full strength. 2,4-D amine is effective on alder, cherry, and madrone when used at full strength.
Application  When using growth regulator herbicides such as triclopyr or picloram, treat the cut area or injection with the undiluted chemical. Use 0.25 tsp (equal to 1 ml) of the undiluted chemical for each cut. Use imazapyr and glyphosate only during summer and fall, but do apply to conifers. Use picloram in any of these seasons in mixture with 2,4-D, but control will be best if picloram is applied in summer. Triclopyr amine is effective in spring, fall, and winter if trees are completely frilled. Space cuts for triclopyr  about 3 inches between centers. Imazapyr cut spacing can be 6 inches on trees up to 12 inches in diameter, and 3 inches on larger maples;  use the more concentrated material in winter.
Application may be made with various types of tree injectors or with a hatchet and squeeze bottle. Tree injectors are tools designed to place chemicals into trees without frilling, girdling, or felling. The objective is to inject the chemical directly into the live tissue of the tree. Injector hatchets permit reaching around trees from one side, and should make this a very useful and low-cost method, particularly since modern chemicals do not require injection at the base of the tree. Imazapyr injections can be widely spaced (6 inches) in species other than maple. 
The hack-and-squirt method is slower than the injector and is less precise in metering chemicals. It offers the advantage of lower investment cost for small jobs. It is not certain that results are comparable to those of injectors, but differences would not be great in any event.
Injecting conifers is probably the cheapest way to thin stands of fewer than 1,000 conifer trees per acre. Total kill is not required, and minimal dosages permit good development of untreated trees. Heavy dosages, particularly of picloram and imazapyr, offer danger of flashback damage to untreated trees. Cutting sprouting hardwood species, especially in winter or spring, often results in prolific regrowth unless stumps are treated. Always treat bigleaf maple  stumps to avoid sprouting. It is often most feasible to kill undesirable hardwoods before harvesting timber so that stumps are not a problem.
Hazards
All methods of forest weeding entail some risks. Some are measurable, such as frequency of accidents. Scientists can evaluate exposure—and to some extent, actual intake—of pesticides, exhaust fumes, fuels, and lubricants, and observe whether worker safety is affected. Evidence to date suggests that physical injury while working in the woods is where greatest improvements in safety can be made.
Much has been publicized about dangers of herbicide residues on treated vegetation. These dangers are generally greatly overrated because once dried on foliage, stems, or organic material, most products are difficult or impossible to dislodge. For most products, liquid contact with skin or food is required to transfer a measurable dose to the body. Harm cannot occur unless a dose actually enters the bloodstream in quantities large enough to trigger a toxic response. With normal use, such exposure occurs only when concentrated liquids are directly ingested in liquid form, or are allowed to stay on large areas of the applicator’s skin for some period; even then, most herbicide products registered for forest use penetrate human skin poorly, and dosage is way below any known harmful level. Cutting instruments, (e.g., chainsaws) generally are a far greater hazard than chemical residues, with effects on hearing and inhalation of exhaust fumes adding to the potential of mechanical injuries from the saw.
Broadcast applications of herbicides have received considerable attention in recent years in connection with the danger to animals and other forms of life. The known toxicity of common brushkilling compounds used on forest lands is rather low (see “Agrichemicals and Their Properties” in this handbook). More important, it is difficult to obtain a measurable exposure after a product has dried on vegetation (see above). Herbicides are designed to work on plant metabolism, and influence features in plants that are not present in animal life. To reduce risk, do not use the more hazardous mechanical treatments.
Chemicals recommended for local use in reforestation have been used to top-kill brush to promote sprouting for deer and small mammals for over 50 yr. Local studies show that deer, small mammals, and amphibians eliminate or degrade phenoxy herbicides, atrazine, and glyphosate with negligible accumulation and no apparent harmful effects. Unless a product is fat soluble or metallic, the body is unlikely to retain it. Direct effects are limited to plants under normal circumstances. Wildlife meat quality has not been affected by these herbicides as used for reforestation or pasture management according to label guidelines.
Pesticide applicators must consider numerous factors. Treating a forest often entails applying chemicals over large areas. Definitions of treatment boundaries and what areas must be free of drift must be very clear. It is always wise for the applicator to avoid unnecessary exposure to all risks, including potentially harmful machines, tools, and chemicals, including fuels and lubricants. It is always wise to consult neighboring landowners before a major spray job and to take the needed precautions to avoid chemical trespass. The benefits from judicious and well-planned herbicide use can be enormous and should not be jeopardized because of poor public relations or careless application.
Picloram is a restricted-use pesticide except in the products Pathway and Tordon RTU. A certified applicator’s license is required for purchase. Atrazine is also now a restricted-use product. Both are low in mammalian toxicity but require special handling because of potential for water contamination and, for picloram, high crop sensitivity.
Always follow directions on the herbicide label. The label is legally binding. The information in this handbook is not intended to be a complete guide to herbicide use. Before using any chemical, read the label recommendations on the container. Before a chemical can be recommended for a specific use, it must be thoroughly tested. Recommendations on the manufacturer’s label, when followed, can prevent many problems arising from the wrong use of a chemical. Because some uses listed on labels are marginally cost effective, they often are not discussed here although they are legal. Herbicide distributors are legally obligated to provide accurate information about their products, and the information they provide on interpretation of labels is legally binding. If you are uncertain about label interpretation, your dealer can help.
Nonchemical operations  Manually controlling brush entails several hazards, some of which can be reduced by intensive training and supervision in the use of cutting equipment. Among the hazards is a high risk of damaging small conifers and of having negligible benefit. Risk of failure (i.e., net benefit) is optimized by removing as many offending plants as possible. Direct physical risks to the user are appreciable; they include cuts, back and knee injuries, inhaling exhaust fumes, handling carcinogenic fuels, bee stings, and poison-oak. For both chronic and acute chemical effects on operators, manual control is likely the least safe choice of weeding. The risk of long-term injuries to backs and knees in addition to serious wounds is the principal source of reported health problems associated with forest weeding.
Special Considerations
Competition from brush is only part of the brush problem in areas due for reforestation. Brush is fine habitat for animals that feed on tree seedlings. Moreover, in heavy stands of brush, dead or alive, substantial shade will weaken trees and considerable debris can fall and crush small seedlings. An ordinary effort to establish trees in established shrub or sprout stands will surely result in failure. It is always best to provide for reforestation before brush becomes well established, and to avoid suppressing conifers by controlling fast-growing species such as alder and maple.
Tree seedlings used for reforestation in brush need to be substantially larger than those used for Christmas trees and planting old fields. Larger seedlings almost always are a good buy because they are more competitive and can tolerate more animal damage than smaller seedlings. Proper stock is an important element in managing competition. Even so, seedlings also may need treatment with repellent or be a species unpalatable to animals. Douglas-fir and western redcedar are attractive to animals and do best with little shade. Douglas-fir seedlings should be at least 24 inches tall for such areas; 30 inches is preferable if you can get them. Live cover uses water as well as shading seedlings, hence generally is undesirable on planted seedlings regardless of species or size unless there is a severe frost problem. All conifer seedlings grow best if free of weed competition for at least 2 yr. After that, vigorous seedlings will dominate most competitors.
Two herbicide applications or more may be desirable for full plantation establishment. Schedule them so that most woody competitor species are controlled the summer before planting (often better before harvesting) with a site-preparation treatment. After planting, maintenance spray with a soil-residual material such as atrazine or hexazinone prolongs brush relief with minimum damage to conifers (see “Recommendations for Grass and Forbs in Plantation Establishment” in this chapter). Never postpone release until trees are under the brush.
Some commonly used herbicides are quite injurious to conifers at high doses or during the growing season. Control complex weed problems before planting, as part of site preparation. Imazapyr or sulfometuron near the maximum label rate can be injurious, even when used as directed. Use maximum rates only in exceptional circumstances. Expect to see stunting injury when imazapyr is applied broadcast over western Oregon conifers at more than 3 oz ai/A; broadcast application over the top of ponderosa pine is not recommended. 
Several precautions will minimize damage from foliage-active products when used for release.
1.  It is almost always risky to add surfactants to any herbicide used for release because of the risk of conifer damage.
2.  Using maximum registered rates of foliage-active products for conifer release often produces symptoms of injury in conifers, so use these rates only when attempting to control hard-to-kill species and when some conifer injury is tolerable.
3.  When applying foliage-active herbicides with ground equipment, do not spray directly into desirable seedlings and saplings because that causes "hot-spots" of heavy application that can result in injury and even mortality.
Special Registration for Forestry
Herbicides should carry on their labels specific recommendations for a particular use. Forests are not included under noncrop labeling, according to recent interpretations of labeling laws. Some products are registered for site preparation only, and some for more general use, including conifer release. 
Herbicide dealers and distributors are required under the Federal Pesticide Control Act of 1972 to ensure that their products are properly labeled and sold only for purposes described on the label. The major herbicides registered for forestry use in Oregon are listed in the tables that follow, and in “Grass Control for Plantation Establishment” in this chapter, with a rating of effectiveness on some important forest species.
General-use Formulations
Some herbicides are registered for general woody species control in areas such as pastures, fence lines, and ditch banks. Some are nonselective in conifers, such as dicamba and certain imazapyr and picloram formulations; others are nonselective only at certain times, such as glyphosate, triclopyr, and 2,4-D. These materials may be useful for site preparation or stand cleanup. Many have been used traditionally in forestry, but be sure to verify current label status and interpretation before proceeding.
Season of Use
Chemicals are used in all seasons for forest weed control, but each chemical produces a particular set of results in each season. Some are effective only a few weeks out of the year; others are selective at certain times and nonselective at others. Dosages and results change with season. Always use chemicals so that you maximize the favorable environment for the desirable species. Follow the label carefully for safety, economy, and good results. 
Invasive Weeds in Forests
Invasive weeds have many opportunities to establish and spread in forests. Many of these species are exotic, but many native species also proliferate when given disturbed soils and protected environments. Landowners are urged to keep these pests under control, if only for the public good. Once such weeds are introduced, they are very costly to eradicate. Avoidance is far cheaper and more effective.
Many invasive species are woody plants that have been propagated and distributed commercially. English holly, English ivy, gorse, and Scotch broom have been planted as ornamentals and have escaped to cover large areas of pasture and cutover forest lands. Himalaya and evergreen blackberries, brought by settlers into this region for their fruit, are popular for recreational picking and eating. Broom and gorse have lovely yellow flowers. All are highly invasive, have persistent seeds, and will occupy ground rapidly. Birds spread them by foraging on fruits and seeds. Deer and other wildlife carry seeds to provide new colonies. These species are equipped to survive many obstacles. Programs to eradicate them may appear successful in the short run but are likely to fail in the longer term. Control requires persistence and good recognition as well as understanding their means of survival and propagation. Establishing a conifer crop that can shade out these exotics is an important approach to managing this problem. For more detail, see the “Control of Problem Weeds” chapter in this handbook.

Some exotic plants are still sold in commercial nurseries. English holly and English ivy pose major long-term problems: they are very tolerant of shade, they flourish under dense second-growth stands, and they are difficult to kill with herbicides normally in a forester’s tool kit (see the “Control of Problem Weeds” chapter in this handbook for more information on ivy control). The key to successful management is early recognition and eradication before plants get big enough to produce seed or reproduce vegetatively. Both ivy and holly produce seeds when growing in shade; hence seedlings must be removed before plants reach seed-bearing size. Ivy, which must climb into upper crowns to produce seeds, will develop crowns capable of shading out second-growth Douglas-fir. Holly can create dense stands from scattered understory seedlings, eventually leading to shade so dense that hemlock trees cannot survive. These attractive plants are serious pests. Periodic inventories of forest stands will determine where problems are likely and where attention should be directed next. For example, holly seedlings are often found along ridgelines where birds tend to roost.

Many invasives are spread by machines, including logging equipment and various motor vehicles. One of the most important conduits for invasives is roads. Road graders, ditch cleaners, bulldozers, car tires, log trucks, and many other types of machinery that travel along roads pick up seeds and vegetative structures and move them to new areas. Maintaining weed-free road shoulders and backslopes is the only certain way to prevent spread. Some landowners require that all equipment brought in to do logging and road work be washed down before entering and leaving the property. 

Weed control programs designed to maintain visibility along roads may help to reduce the spread of invasive species. They also provide unoccupied habitat where seeds, viable stem pieces, and whole plants have room to grow. Unless sources of contaminating plant material are kept under control, these species will spread through a road system and into clearcuts or otherwise disturbed areas. Use herbicide mixtures that favor the establishment of competitive cover such as low-flammability grasses while removing brush, and use native plants that are less likely to become weeds themselves. Low, dense vegetation beyond the road shoulders is a good way to minimize invaders.  

Keep a road system relatively free from invasives by maintaining a section of road right-of-way that will prevent invasives from moving effectively. Control of vegetation on road shoulders with a broad-spectrum herbicide that inhibits germination or vegetative propagation can be effective if the general road system is relatively clean of invasives. Patrol these roads two to three times each summer to recognize and control small invasions, and thus prevent their spread. Clean-up of small patches is far cheaper than clean-up of established exotic stands.

Many species, such as horseweed (often known as marestail), spread very rapidly after fire or clearcutting, especially if other weeds (i.e., cover that competes with invasives) are controlled with products with little residual action in late spring. Horseweed germinates later than many weeds and also can develop herbicide resistance. Certain products (e.g., clopyralid and aminopyralid) will control this weed.

Blackberries (Himalaya and evergreen species) are especially troublesome along rights-of-way where they spread across fences. Herbaceous species too numerous to mention are capable of colonizing new clearcuts and understories of thinned stands. Species such as Brachypodium (false brome), prickly lettuce, sweet cicely, (a native or naturalized exotic), Roberts geranium, and many others will invade disturbed understory sites and exclude native herbs. Where wildlife species prefer native plants for forage, the invasives may degrade habitat. One seldom knows the true cost of such invasions, yet the mixture of these invaders may be difficult to control economically until the site becomes occupied with desirable and dominant cover.

The diversity of invasive plants almost guarantees failure to control all of them. Clearly, the best control is a dominant cover with a group of species that casts a dense shade. Douglas-fir and western redcedar are very valuable species that cast dense shade from about ages 13 to 40 yr in unthinned stands. Western hemlock and grand fir may provide better shade than Douglas-fir and cedar but are lower in value. Regardless of the overstory species present, thinning will offer new opportunities for invasives as well as increase the growth of the crop conifers. It will be essential to follow thinning with a weed control program designed to avoid damaging overstory trees and desirable forage species. This technology is in its infancy.

Little research has been done on how to minimize invasives in clearcuts or thinned stands without damaging desirable species, and it is unlikely there will be extensive research on controlling the diversity of pests now present. Establishing a competitive cover may increase competition with the crop species, yet having open ground increases the risk of exotic intrusion. Identification of potential invasive species is essential, so that appropriate and common controls can most effectively prevent their establishment. Many herbicides and herbicide combinations are registered for use in young stands, and each will control a certain spectrum of weeds, depending on dosage and time of application. The nature of disturbance in the logging operation also will influence the composition of invaders. Site history (i.e., whether broom, blackberries, gorse, or other plants with persistent seeds were present before the current stand was harvested) will provide warning of a seed bank not yet emerged. One problem that will get worse is treatment tolerance: some exotic species may have a certain percentage of plants that tolerate a given treatment, and over time these may become a resistant species. It is especially important to remove such resistant individuals before they spread across the landscape. This, however, requires surveillance beyond most of our capabilities, and this problem will require extensive attention. 

Effectiveness of Major Forestry-registered Herbicides
during Seasons of Optimum Usage             

Species	atrazine
(spring)	clopyralid
(all)	glyphosate
(late summer)	picloram
(all)	2,4-D
(spring, fall)	hexazinone
(spring)	sulfometuron
(fall)	metsulfuron
(summer)	metsulfuron
(fall)	triclopyr  ester (spring)	imazapyr
(late summer)	
Conifers
Douglas-fir	
R	
R	
I-R	
S	
I-R	
R	
I-R	
S	
I	
I	
I	
Firs, true	R	R	R	S	S-I	R	R	S	—	I	I	
Hemlock	I-R	R	I-R	S	I-R	R	R	S	—	I	I	
Pines	R	R	I-R	I-S	S-I	R	R	S	—	S	I	
Redcedar, western	I-R	R	S	S	S	S	I-R	S	I-R	S	—	
Woody Species
Alder			
I	
S	
I-S	
I-R	
I-R	
R	
R	
S	
S	
Blackberry			I	S	R	I	I	S	S	S	I-R	
Cascara			S	I	I	R	—	I	—	S	I	
Ceanothus spp.			I-R*	—	S	I	—	I	—	S	S	
Cherry 			S	S	S	R	—	S	—	I	S	
Chinquapin 			I-R*	—	I	R	—	I	—	S	—	
Elderberry		S	S	S	R	R	—	S	R	S	S	
Hazel			S	I	I	R	—	—	—	I	S	
Madrone			I-R*	S	S	R	—	I	—	I	S	
Manzanita spp.			R	S	S	R	—	I	—	R	R	
Maple, bigleaf			I	I	R	R	R	R	R	I	S	
Maple, vine			S	I-S	R	R	R	R	R	I-S	S	
Poison-oak			S	S	R	R	R	—	—	I-S	S	
Salmonberry			S	I	R	I	I	S	S	I	I	
Snowberry			S	—	I-S		—	—	—	I	—	
Tanoak			R	S	I	R	R	I	—	I-S	I	
Thimbleberry			S	I	I	I	I	S	S	I	I	
Willow spp.			S	I-S	R-S	R	—	—	—	I-S	—	
Herbs
Fern, bracken	
I		
I-S	
I	
R	
I	
S	
S		
R	
—	
Fern, sword	R		I	R	R	R	I-S	S		R	—	
Grasses, annual 	S		S	R	R	S	S	R		R	S	
Grasses, perennial	S-R		S	R	R	S	S	R		R	S	
Herbs, broadleaf	I	S**	S	S-I	S	S	S-R	S-R		I-S	S	
R = resistant to highest rates.  I = intermediate or variable; highest rates effective.  S = sensitive; killed by medium or lower rates.
* Glyphosate has intermediate activity if applied after full leaf expansion but before wax develops on leaves of evergreen species; it has marginal conifer selectivity in spring.
** Clopyralid has activity on selected broadleaf weeds such as Canada thistle and other thistles. See the Washington, Oregon, and Idaho special local needs labels for Transline for more details.

Recommendations for Directed Spot Spray, Tree Injection, 
and Basal Bark Treatment

Species	

Herbicide1	Active chemical per 100 gal of solution	

Carrier	

Expected control	

Application and remarks	
Alder, red
Alnus rubra	2,4-D	2 lb	Water	Excellent	Foliage spray. See label for release timing.	
	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Excellent	Foliage spray. Site prep only.	
	2,4-D amine	undiluted	None	Good	Injection, 3 inches between centers, 1‑2 ml/injection.	
	picloram + 2,4-D	undiluted	None	Good	Injection, 3 inches between centers.	
	triclopyr ester	0.75 gal	Water		Midsummer directed foliage spray.	
	triclopyr amine	half strength	Water	Excellent	Injection, 3–4 inches between centers. Use full strength in maple and tanoak.	
	triclopyr ester	4–8 lb undiluted	Oil	Excellent	Basal treatment, any season. Thinline basal bark treatment.	
	glyphosate	3 lb ae	Water	Good to excellent	Foliage spray, July. Injection, cut stump.	
	imazapyr	quarter strength	Water	Excellent	Trunk injections, 6 inches between centers.	
		10 lb (2.5%)	Water	Excellent	Low-volume sprays June–Aug. on sprout clumps.	
Ash, Oregon
Fraxinus latifolia	triclopyr amine	3 lb	Water	Excellent	Foliage spray.	
	triclopyr ester	3 lb	Water	Excellent	Directed foliage spray.	
Blackberries
  Himalaya 
  Rubus procerus  
  Evergreen 
  R. laciniatus  
  Trailing
  R. vitifolius	glyphosate	3 lb ae	Water	Good	Sept.–Oct., as long as most foliage is still green.	
	metsulfuron	2 oz	Water	Excellent	Spring, summer, fall site prep.	
	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Good	Foliage spray. Aug.–Sept. Site prep only.	
	triclopyr ester	3 lb	Water	Excellent	Spring to midsummer directed foliage spray.	
	triclopyr amine	2 to 3 lb	Water	Good	Midsummer foliage spray.	
	metsulfuron	2 oz	Water	Excellent	Spring–summer.	
	picloram + 2,4-D	1 gal (0.54 + 
2 lb ae)	Water	Good	Foliage spray. Site prep only.	
	triclopyr amine	2 to 3 lb	Water	Good	Midsummer foliage spray. Use directed spray around pines.	
	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Good	Foliage spray. Site prep only.	
	triclopyr amine	2–3 lb	Water	Good	Midsummer foliage spray. Directed application.	
	triclopyr ester	3 lb	Water	Fair to good	Midsummer directed foliage spray.	
	glyphosate	3 lb ae	Water	Excellent	Aug.–Sept.	
	aminopyralid + triclopyr amine	6–9 pints (0.075 + 0.75 to 0.11 + 1.12 lb)	Water	Good to excellent	Midsummer to fall foliage spray	
*Based on results in southwestern Oregon.  **Adding 2 to 5% oil as an emulsion gives best results.
1Herbicides listed in these recommendations generally have broadly inclusive labels, in terms of effectiveness at concentrations given. Concentrations and dosages suggested here are not necessarily listed on product labels for each species. The recommendations here are based on the best experience available and do not exceed rates recommended for various uses on the labels. Deviations from specific labels are primarily to include species other than those for which product data were available at the time latest labels were issued. New regulations regarding use and current label coverage should be consulted before purchasing a particular product. Aminopyralid  (Milestone) now is registered for trunk injection and cut-stump treatment. Apply 1 cc per injection or axe cut, and overlap cuts for best results. Susceptible species are not yet listed on the label.

DIRECTED SPOT SPRAY, TREE INJECTION, AND BASAL BARK TREATMENT (contd.)

Species	

Herbicide1	Active chemical per 100 gal of solution	

Carrier	

Expected control	

Application and remarks	
All Rubus spp. 	metsulfuron	2 oz	Water	Excellent	June–Sept. Kills conifers.	
Broom, Scotch
Cytisus scoparius	2,4-D	2 lb	Water-oil emulsion	Excellent	March. See label for release timing.	
	triclopyr ester	basal 4–8 lb; foliar 2–4 lb	Oil	Excellent	Basal/foliage spray July–Aug. or March broadcast.	
	aminopyralid + triclopyr amine	6–9 pints (0.075 + 0.75 to 0.11 + 1.12 lb)	Water	Good to excellent	Optimum at bud to bloom	
Cascara, buckthorn 
Rhamnus purshiana	glyphosate	3–4.5 lb ae	Water	Good	Midsummer to late summer.	
Ceanothus spp.*   Mountain whitehorn 
  C. cordulatus
 Blue blossom 
  C.  thyrsiflorus  Snowbrush 
  C. velutinus  
Deerbrush
  C. integerrimus	triclopyr ester	3 lb	Water	Good to excellent	Midsummer directed foliage spray.	
	imazapyr	1 lb	Water	Good to excellent	Midsummer directed foliage spray.	
	2,4-D	2 lb	Water	Excellent	Foliage spray. See label for release timing.	
	glyphosate	3 lb ae	Water	Excellent	Sept., foliage spray. Deerbrush only.	
	aminopyralid + triclopyr amine	6–9 pints (0.075 + 0.75 to 0.11 + 1.12 lb)	Water	Good 	Foliage spray.	
Cherry, bitter 
  Prunus emarginata 
  Himalaya
  P. procerus 
  Chokecherry
  P. virginiana	picloram + 2,4-D	1 gal (0.54 to 
2 lb ae)	Water	Good to excellent	Foliage spray. Site prep only.	
	glyphosate	3 lb ae	Water	Excellent	Sept., foliage spray.	
	2,4-D amine	undiluted	None	Excellent	Injection or frill June–Aug.	
	triclopyr ester	4–8 lb	Oil	Excellent	Basal spray. Nov.–Feb.	
	triclopyr ester	undiluted	None	—	Thinline basal bark treatment.	
	metsulfuron	2 oz	Water	Excellent	June foliage spray.	
	2,4-D amine	undiluted	None	Excellent	Injection, stump treatment, or frill June–Aug.	
Chinquapin 
Castanopsis spp. 	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Good	Foliage spray. Site prep only.	
	2,4-D amine	undiluted	None	Good	Frill treatment.	
	triclopyr ester	4 lb	Water	Excellent	Foliage spray. Directed spray.	
		4–8 lb	Oil	Excellent	Basal spray.	
Coffeeberry 
Rhamnus californica	2,4-D	4 lb	Water**	Poor	Directed foliage spray or site prep	
	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Good	Foliage spray. Site prep only.	
Cottonwood 
Populus trichocarpa	2,4-D amine	undiluted	None	Good	Frill treatment or injection.	
	triclopyr ester	4–8 lb	Oil	Excellent	Basal spray.	
	glyphosate	3 lb ae	Water	Excellent	Foliage spray, July–Aug. Not recommended in Idaho.	
	metsulfuron	0.6 oz 
+ silicon
surfactant	Water	Excellent	Full foliar.	
Currants and Gooseberries 
Ribes spp. 	2,4-D + picloram	1 gal	Water	Good	Summer.	
	glyphosate	1 gal	Water	Poor	Summer–fall.	
DIRECTED SPOT SPRAY, TREE INJECTION, AND BASAL BARK TREATMENT (contd.)

Species	

Herbicide1	Active chemical per 100 gal of solution	

Carrier	

Expected control	

Application and remarks	
Douglas-fir 
Pseudotsuga menziesii	picloram + 2,4-D	2 gal (1.08 + 
4 lb ae)	Water	Good	Roadside spray.	
	glyphosate	capsules	None	Excellent	Capsule injection.	
	picloram + 2,4-D	undiluted	None	Excellent	Injection (thinning) fall-winter.	
	metsulfuron	4 oz	Water	Poor to excellent	Full foliage spray, spring.	
Elderberry, red 
Sambucus callicarpa	glyphosate	3 lb ae	Water	Excellent	July–Sept.	
	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Excellent	Foliage spray, summer.	
	triclopyr	3 lb ae	Water	Excellent	June–July.	
Gorse 
Ulex europaeus	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Excellent	Foliage spray. Best on younger plants. Site prep only.	
	triclopyr	1 to 2 gal	Water	Excellent	Spring.	
	metsulfuron	2 oz 
+ surfactant	Water	Excellent	Spring.	
Hazel 
Corylus cornuta var. 
  californica	glyphosate	3 lb ae	Water	Excellent	Late summer foliage spray.	
	triclopyr ester	4–8 lb	Oil	Excellent	Basal spray.	
Madrone 
Arbutus menziesii	2,4-D ester	4 lb	Water	Good	Directed foliage spray/site prep, spring/summer.	
	2,4-D amine	undiluted		Excellent	Injection, 1–2 ml/inch of diameter	
	triclopyr ester	2–3 lb	Water	Fair	Midsummer directed foliage spray.	
		4–8 lb	Oil	Excellent	Basal spray.	
	imazapyr	25% strength	Water	Excellent	Injection, 6–9 inches between centers.	
	glyphosate	50% to full	Water	Excellent	Cut stump/injection.	
Manzanita*
  Hairy 
  Arctostaphylos 
    columbiana
  Hoary 
  A. canescens 
  Pine 
  A. parryana
  Whiteleaf 
  A. viscida
  Greenleaf 
  A. patula
  Howell’s
  A. hispidula	
2,4-D	
2 lb	
Water**	
Good	
Foliage spray. See label for release timing.	
	2,4-D	2 lb	Water**	Good	Foliage spray. See label for release timing.	
	2,4-D 	2 lb	Water**	Good	Foliage spray. See label for release timing.	
	2,4-D 	2 lb	Water**	Good	Foliage spray. See label for release timing.	
	2,4-D 	2 lb	Water**	Poor to fair	Retreat sprouts if needed; foliage spray. See label for release timing.	
	triclopyr ester	2–3 lb	Water	Poor to fair	Midsummer directed foliage spray. Not recommended in Idaho.	
		4–8 lb	Oil	Excellent	Basal spray.	
	2,4-D 	2 lb	Water	Good	Foliage spray. See label for release timing.	
*Based on results in southwestern Oregon.
**Adding 2 to 5% oil as an emulsion gives best results.
1Herbicides listed in these recommendations generally have broadly inclusive labels, in terms of effectiveness at concentrations given. Concentrations and dosages suggested here are not necessarily listed on product labels for each species. The recommendations here are based on the best experience available and do not exceed rates recommended for various uses on the labels. Deviations from specific labels are primarily to include species other than those for which product data were available at the time latest labels were issued. New regulations regarding use and current label coverage should be consulted before purchasing a particular product. Aminopyralid  (Milestone) now is registered for trunk injection and cut-stump treatment. Apply 1 cc per injection or axe cut, and overlap cuts for best results. Susceptible species are not yet listed on the label.

DIRECTED SPOT SPRAY, TREE INJECTION, AND BASAL BARK TREATMENT (contd.)

Species	

Herbicide1	Active chemical per 100 gal of solution	

Carrier	

Expected control	

Application and remarks	
Maple*
  Bigleaf
  Acer macrophyllum
  Vine 
  A. circinatum	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Fair	Site prep only.	
	imazapyr (4 lb/gal)	25–50% strength	Water	Excellent	Injection summer–fall.	
		10 lb (2.5%)	Water	Excellent	Foliage spray on sprout clumps. Very low volume.	
	triclopyr amine 	undiluted		Excellent	Injection, half-strength for trees less than 12 inches or for stump treatment.	
	triclopyr ester	4 lb	Water	Fair	Foliage spray of sprout clumps. Not for conifer release.	
	triclopyr ester	12 lb (3%)	Oil	Good to excellent	Basal treatment.	
		undiluted to half strength	None/oil	Good to excellent	Thinline basal bark treatment.	
		30% strength	Oil	Good to excellent	Low-volume basal bark treatment.	
	picloram + 2,4-D	undiluted	None	Excellent	Frill, injection, or stump.	
	glyphosate	3 lb ae	Water	Good	Foliage spray, late summer.	
	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Good	Foliage spray. Site prep only.	
	triclopyr ester	12 lb	Oil	Good to excellent	Basal treatment.	
		undiluted to 50% strength	None/oil	Good to excellent	Thinline basal bark treatment.	
		30% strength	Oil	Good to excellent	Low-volume basal bark treatment.	
	imazapyr	1 lb	Water	Excellent	Foliage spray.	
Oak
  Oregon 
  Quercus garryana
  California black 
  Q. kelloggii
  Canyon live 
  Q. chrysolepis	glyphosate	3 lb ae	Water	Excellent	Foliage spray.	
	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Excellent	Foliage spray. Site prep only.	
	2,4-D amine or glyphosate	undiluted	None	Excellent	Frill; good on all oaks.	
	triclopyr ester	2–3 lb	Water	Good	Directed foliage spray. Good on all oaks.	
		4–8 lb	Oil		Basal treatment. Good on all oaks.	
	imazapyr	25% strength	Water	Excellent	Cut surface or injection, 
6 inches between centers.	
	metsulfuron	0.6 oz 
+ silicon
surfactant	Water	Excellent	Full foliar.	
	2,4-D	4 lb	Water**	Good	Directed foliage spray or site prep, May–July. May be necessary to re-treat.	
	triclopyr ester	4–8 lb	Oil	Excellent	Basal spray.	
DIRECTED SPOT SPRAY, TREE INJECTION, AND BASAL BARK TREATMENT (contd.)

Species	

Herbicide1	Active chemical per 100 gal of solution	

Carrier	

Expected control	

Application and remarks	
Pine 
  Lodgepole 
  Pinus contorta
  Ponderosa 
  P. ponderosa	
triclopyr amine	
3 lb	
None	
Good	
Injection; one cut per 3-inch circumference. May–Sept.	
	metsulfuron	0.6 oz 
+ silicon
surfactant	Water	Good	Spring, after budbreak.	
	triclopyr amine	3 lb	None	Good	Injection; one cut per 3-inch circumference. May–Sept.	
	triclopyr ester or 2,4-D ester	4 lb	Water/oil	Excellent	Foliage spray April–June.	
Poison-oak
Toxicodendron 
   diversilobum	triclopyr ester	2–3 lb	Water	Good to excellent	Directed foliage spray. Spring application best.	
	glyphosate or imazapyr	6 lb ae1 lb ae	Water	Excellent	Foliage spray July–Aug. (before color).	
	2,4-D	4 lb	Water	Fair to poor	Directed foliage spray or site prep. Re-treat sprouts.	
	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Fair	Foliage spray. Site prep only.	
	imazapyr	1 lb	Water	Excellent	Site prep only.	
	aminopyralid + triclopyr amine 	6–9 pints (0.075 + 0.75 to 0.11 + 1.12 lb)	Water	Good 	Foliage spray. Spring application best.	
Rhododendron 
Rhododendron 
   macrophyllum	triclopyr ester	4 lb	Water/oil	Fair to good	Spring foliage spray.	
Salal 
Gaultheria shallon	triclopyr ester	4 lb	Water	Fair	Summer foliage spray. Site prep only.	
	picloram	2 lb	Water	Good	Summer foliage spray. Site prep only.	
	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Fair	Foliage spray. Site prep only.	
	imazapyr	10 lb (2.5%)	Water	Good	Low volume.	
Salmonberry 
Rubus spectabilis	glyphosate	3 lb	Water	Excellent	July–Sept.; Sept. only for release.	
	metsulfuron	1 oz	Water	Excellent	June–July. Injures conifers.	
	sulfometuron	4 oz	Water	Good	April–May.	
Serviceberry 
Amelanchier spp. 	2,4-D	2 lb	Water**	Poor to fair	Foliage spray. Several treatments required. See label for release timing.	
	glyphosate	3 lb ae	Water	Good	Summer–fall.	
	triclopyr ester	2–3 lb	Water	Good	Directed foliage spray.	
Snowberry 
Symphoricarpos albus	glyphosate	4 lb ae	Water	Excellent	Foliage spray July–Sept. Not recommended in Idaho.	
	metsulfuron	0.6 oz 
+ silicone
surfactant	Water	Excellent	Full foliar.	
	triclopyr ester	2–3 lb ae	Water	Fair	Foliage spray.	
*Based on results in southwestern Oregon.
**Adding 2–5% oil as an emulsion gives best results. 
1Herbicides listed in these recommendations generally have broadly inclusive labels, in terms of effectiveness at concentrations given. Concentrations and dosages suggested here are not necessarily listed on product labels for each species. The recommendations here are based on the best experience available and do not exceed rates recommended for various uses on the labels. Deviations from specific labels are primarily to include species other than those for which product data were available at the time latest labels were issued. New regulations regarding use and current label coverage should be consulted before purchasing a particular product. Aminopyralid  (Milestone) now is registered for trunk injection and cut-stump treatment. Apply 1 cc per injection or axe cut, and overlap cuts for best results. Susceptible species are not yet listed on the label.

DIRECTED SPOT SPRAY, TREE INJECTION, AND BASAL BARK TREATMENT (contd.)
Sweetbriar rose 
Rosa eglanteria	picloram + 2,4-D	1 gal (0.5 + 2 lb ae)	Water	Good	Good initial kill, some retreatment on sprouts. Site prep only.	
	triclopyr ester	2–3 lb	Water	Good	Directed foliage spray.	
	glyphosate	3 lb ae	Water	Good	Directed foliage spray.	
Tanoak* 
Lithocarpus densiflora	2,4-D	4 lb ae		Poor	Directed foliage spray. Several treatments needed.	
	triclopyr amine	Undiluted	—	Excellent	Injection any season,
4 in between centers.	
	triclopyr ester	3–5% strength	Oil	Good to excellent	Basal treatment. Best to treat third-year sprouts.	
Thimbleberry 
Rubus parviflorus	picloram + 2,4-D	1 gal (0.54 
+ 2 lb ae)	Water	Good	Foliage spray. Re-treatment may be required. Site prep only.	
	glyphosate	3 lb ae	Water	Excellent	Foliage spray, July–Sept.	
	metsulfuron	0.6 oz 
+ silicon
surfactant	Water	Excellent	Full foliar.	
Willow
Salix spp. 

Note: Oregon’s many species of willow vary in susceptibility. These are starting recommendations. 	2,4-D	2 lb ae	Water	Good	Foliage spray. May need to retreat sprouts. See label for release timing.	
	triclopyr ester	2–3 lb	Water	Good	Directed foliage spray.	
		4–8 lb	Oil		Basal treatment.	
	glyphosate	3 lb ae	Water	Fair to good	Foliage spray July–Sept. 	
	metsulfuron	0.6 oz
+ silicon
surfactant	Water	Excellent	Full foliar.	
	imazapyr 
+ glyphosate	0.5 lb ae 
+ 3 lb ae	Water	Good to excellent	Foliage spray July–Sept.	

*Based on results in southwestern Oregon.
**Adding 2–5% oil as an emulsion gives best results.
1Herbicides listed in these recommendations generally have broadly inclusive labels, in terms of effectiveness at concentrations given. Concentrations and dosages suggested here are not necessarily listed on product labels for each species. The recommendations here are based on the best experience available and do not exceed rates recommended for various uses on the labels. Deviations from specific labels are primarily to include species other than those for which product data were available at the time latest labels were issued. New regulations regarding use and current label coverage should be consulted before purchasing a particular product. Aminopyralid  (Milestone) now is registered for trunk injection and cut-stump treatment. Apply 1 cc per injection or axe cut, and overlap cuts for best results. Susceptible species are not yet listed on the label.

Recommendations for Area Spraying Using Boomless Ground Equipment or Aircraft

Several products containing recommended active ingredients may be available for application with boomless ground equipment or aircraft. Before you buy, be sure that proposed uses comply with label restrictions. This is especially true for chemicals used specifically for growing tree crops.
In most cases, it is preferable to spray 2,4-D or triclopyr with aircraft late in the dormant season to avoid injuring Douglas-fir, hemlock, or true firs. Glyphosate and/or imazapyr are effective and selective in later summer, after conifer buds have hardened. Pines are very sensitive to 2,4-D or triclopyr between March and early July. In most situations, helicopter and broadcast ground applications with coarse sprays (VMD 1,000 microns or less) drift less and are as effective as finer sprays. Boomless nozzles cannot project fine drops to the edges of their swaths. They are best suited for soil-residual products and those with good systemic activity if applied in large drops, for example, hexazinone, glyphosate, and imazapyr. Aminopyralid is newly registered for use on herbaceous vegetation in site preparation, and for mixtures with other registered herbicides to broaden spectrum of activity. The list of sensitive species is yet incomplete, but a wide variety of broadleaf species is susceptible. Release uses will injure conifers unless spray is hand-directed to avoid conifers. Do not exceed 9 pints/A Milestone in broadcast applications.

Restricted-use Formulations
Picloram is designated as a restricted-use pesticide. All users must be certified to purchase or apply products containing it. 
Machine Clearing
In some circumstances, scarification with a bulldozer is feasible. Use toothed or conventional blades to remove brush on gentle topography. Do this when soil is very dry to minimize damage. Combining partial scarification with chemicals often offers the advantages of both procedures. In any event, keep soil compaction to a minimum. The operator should anticipate that scarification may set up a seedbed for an entirely new weed problem that can compromise results. Follow-up weed control is often needed. Burn or scatter piles of brush to improve plantability and reduce animal damage. 
RECOMMENDATIONS FOR AREA SPRAYING USING BOOMLESS GROUND EQUIPMENT OR AIRCRAFT

Species	
Herbicide	Active chemical/A	Gal of spray/A	
Carrier	Expected
control	Application
and remarks	
Alder, red
Alnus rubra	2,4-D	2 lb	10	Water*	Good	Foliage spray. Best on trees under 10 yr. old. See label for release timing.	
		2 lb	10	Oil	Good	Dormant spray before conifer bud break, April and early May.	
	picloram 
+ 2,4-D	0.5 lb 
+ 2 lb	10	Water	Good	Foliage spray. Badly injures conifers. Site prep only.	
	glyphosate	0.75–
1.5 lb ae	10	Water	Good	June, Aug.–Sept. under 10 ft tall. June injures conifers.	
	triclopyr amine	6–9 lb	10	Water	Excellent	Midsummer foliage spray. Site prep only at this time.	
	triclopyr ester	1.25–2 lb	10	Oil/Water	Excellent	Severely injures pines. Release. Use oil for dormant treatment. Use water only for early foliar treatments. See label for higher rates for site prep.	
Broom, Scotch
Cytisus scoparius	2,4-D	2 lb	5 to 10	Water 
+ 5% oil	Good	Early spring foliage spray. Will reproduce from seed; some sprouting.	
	2,4-D	2 lb	5 to 10	Oil	Excellent	Feb.–March dormant spray. Will reproduce from seed; little sprouting.	
	picloram 
+ 2,4-D	0.5 lb 
+ 1–1.5 lb	10	Water	Good	Site prep only; summer to fall.	
	triclopyr ester	1–1.2 lb	10	Oil/water	Good	Dormant release.	
* 10% oil in carrier
RECOMMENDATIONS FOR AREA SPRAYING USING BOOMLESS GROUND EQUIPMENT OR AIRCRAFT (contd.)
	aminopyralid + triclopyr amine	6–9 pints (0.075 + 0.75–0.11 + 1.12 lb)	15	Water	Good to excellent	Site prep only or directed spray.  Keep spray from contacting trees.	
Ceanothus spp.	picloram 
+ 2,4-D	1 gal (0.54 + 2 lb ae)	15			Foliage spray. Site prep only.	
	triclopyr ester	1.25–2 lb	10	Oil/Water	Fair to excellent	Foliage spray or dormant. See label for rates above 1.5 lb and for timing. Do not use on pines.	
	2,4-D	2–3 lb	10	Water*	Fair to excellent	Early foliar. 2,4-D rates above 2 lb may injure some conifers. See label. 	
	2,4-D 
+ triclopyr ester	2 lb + 1 lb	10	Water	Good to excellent	Can control some associated species; spring, late summer. See label for timing. Do not use on pines. Good conifer release treatment in spring.	
	fluroxypyr	2.66 pints	10	Water	Excellent	Site prep for pine only. Reduced rates suitable for release.	
Cherry, bitter
Prunus emarginata	imazapyr 
+ glyphosate	4 to 6 fl oz +  1.5–2 lb	10	Water	Excellent	Site prep only.	
Elderberry
Sambucus spp. 	picloram 
+ 2,4-D	1 gal (0.54 + 2 lb ae)	15	Water	Excellent	Foliage spray. Site prep only.	
	glyphosate	0.75–1.1 lb	10	Water	Excellent	Sept. foliage release spray. Higher rate for site prep. Add 2–2.5 oz/A imazapyr to broaden spectrum.	
	triclopyr ester	1.25 lb	10	Water	Good to excellent	Site prep. See label for application timing. Do not use on pines.	
	clopyralid	3–5 oz ai/A	10	Water	Good to excellent	Use when plants are actively growing.	
Gorse
Ulex europaeus	picloram 
+ 2,4-D	2 gal (1.08 + 4 lb ae)	15	Water	Good	Good enough control for reforestation but not for eradication. Site prep only.	
	metsulfuron	2 oz ai/A	10	Water 
+ 0.15% silicon-based surfactant	Excellent	New Zealand data. Site prep only. Wait at least 6 mo before planting.	
	triclopyr ester	1–1.5 lb	10 to 15	Water	Excellent	Spring.	
RECOMMENDATIONS FOR AREA SPRAYING USING BOOMLESS GROUND EQUIPMENT OR AIRCRAFT (contd.)
Madrone 
Arbutus spp. 	2,4-D	3 lb	10	Water	Good to excellent	Associated species may be difficult to control. Rates above 2 lb (1 lb 2,4‑D for pines) may injure conifers. Spring treatment best.	
	triclopyr ester	1.25 lb	10	Water	Fair to excellent	Use lower rate before conifer bud swell for release. Do not use over 
2- or 3-needle pines.	
	picloram + 
triclopyr ester	1 lb 
+ 1–2 lb	10	Water	Good to excellent	Site prep only. Not recommended in Idaho.	
	triclopyr ester 
+ 2,4-D	1 lb + 2 lb	10	Water	Good to excellent	Early summer before conifer budbreak. Can control some associated species. Do not use on pines.	
	fluroxypyr	2.66 pints	10	Water	Excellent	Pine plantations only; use highest rates only for site prep.	
*10% oil in carrier
RECOMMENDATIONS FOR AREA SPRAYING USING BOOMLESS GROUND EQUIPMENT OR AIRCRAFT (contd.)
Manzanita
Arctostaphylos spp. 	2,4-D	2 lb	5 –10	Water*	Good	Associated species may be hard to control. See label for release timing.	
	triclopyr ester	1.25 lb	10	Water	Poor	Early foliage spray release. Erratic. See label for timing. Do not use over pines.	
	fluroxypyr	2.66 pints		10	Good	Highest rates for site prep only. Should be safe at reduced rates on pine plantations.	
Maple
  Bigleaf
  Acer 
    macrophyllum  
  Vine
  A. circinatum	picloram 
+ 2,4-D	2 gal (1.08 + 4 lb ae)	15	Water	Fair	Foliage spray. Better controlled with basal or frill treatments on large trees. Site prep only.	
	imazapyr 	0.2–0.25 lb ai	10	Water	Good to excellent	Release or site prep. Late summer for release. Add 0.75–1.5 lb/A glyphosate to broaden spectrum.	
	glyphosate	0.75 to 1.5 lb ae	10	Water	Fair to good	Sept. foliar. Add imazapyr at 0.2 lb/A for best results.	
	picloram
+ 2,4-D 	2 gal (1.08 + 4 lb ae)	15	Water	Fair	Site prep only.	
	imazapyr 	2 oz ae	10	Water	Excellent	Foliage spray. Add glyphosate at 
1 quart/A to broaden spectrum.	
	glyphosate	0.75–1.1 lb ae	10	Water	Good	Sept. release spray; 1.5 lb. Can go up to 3 lb ae for site prep Add imazapyr at 1–2 oz/A for best results.	
	triclopyr ester	1.25–1.5 lb	10	Oil	Excellent	Dormant spray, spring. Do not use on pines. Higher rate may injure Douglas-fir.	
	picloram + triclopyr ester	1 lb + 1–2 lb	10	Water	Good to excellent	Site prep only, summer. Not recommended in Idaho.	
Poison-oak
Toxicodendron 
  diversilobum	imazapyr	0.2 lb/A	10	Water	Excellent	Foliage spray. Apply in fall for release. Kills grass, herbs.	
	glyphosate	 0.75–1.5 lb ae	10	Water	Excellent	July–Aug. Kills grass too. May be mixed with imazapyr.	
	aminopyralid + triclopyr amine	6–9 pints (0.075 + 0.75–0.11 + 1.12 lb)	15	Good 		Site prep or directed spray only. Keep spray from contacting conifers	
Salmonberry
Rubus 
  spectabilis	picloram 
+ 2,4-D	1 gal (0.54 + 2 lb ae)	15	Water	Good	Site prep only.	
	glyphosate	0.75–1.1 lb ae	10	Water	Excellent	Aug.–Sept. foliage spray. Good for site prep, release.	
	metsulfuron	0.5 oz ai	10	Water	Excellent	Site prep.	
Tanoak
Lithocarpus 
  densiflora	triclopyr ester	1.25 lb	10	Water/Oil	Good	Apply prebud swell for conifer release. Do not use on pines.	
	2,4-D	2–3 lb	10	Water	Fair	Spring. Summer treatment may injure conifers after bud burst.	
	picloram + triclopyr ester	1 lb + 1–2 lb ae	10	Water	Good	Site prep only, summer. Not recommended in Idaho.	
Willow
 Salix spp.	2,4-D	2 lb	5–10	Water*	Fair to good	Foliage spray. Retreatment of sprouts necessary. See label for release timing.	
	picloram 
+ 2,4-D	2 gal (1.08 + 4 lb ae)	15	Water	Good	Foliage spray. Site prep only.	
	imazapyr 
+ glyphosate	0.2–0.4 lb + 1.5–3 lb ae	10	Water	Excellent	Site prep only.	
* 10% oil in carrier

Grass and Herb Control for Plantation Establishment
Planting conifers on fields with heavy grass usually reduces plantation survival. A moderately dense stand of grass in an open field in western Oregon can be expected to remove virtually all available moisture in the top 12 inches of soil by the end of June. Removing the grass gives seedlings much of the water that the grass would have transpired. Tillage may be used, but mechanized equipment must be able to negotiate the terrain. The advantage of herbicides is that a single treatment gives complete weed control the first season and may give partial weed control in later seasons. The same pertains to Christmas trees or reforestation. Christmas trees, however, involve additional considerations, which are discussed in a separate section of this handbook.
Herbicides
The most effective herbicides for this use have been the triazines: atrazine and hexazinone (Velpar) and sulfometuron. The triazine-type herbicides provide relatively good weed control for an extended period at rates of 3 to 4.4 lb/A of the 90% atrazine and 1 to 2 lb ai of hexazinone. Many conifers tolerate hexazinone, and it gives excellent control of some atrazine-resistant weeds. Glyphosate also provides complete, selective control of many resistant weeds but may injure conifers in spring. At present, mixtures can be applied according to the rates of individual components registered for use in forestry. Some products are registered for preplant application only. Preceding tables in this section summarize current recommendations for both reforestation and Christmas trees. Sulfometuron is used in fall on 1- to 4-yr-old plantations to control grasses, forbs, ferns, and brambles. A broadleaf product such as clopyralid may be needed in the tank-mix. Aminopyralid  recently was registered for use, alone or in tank-mixes, on herbaceous vegetation during site preparation; do not apply over desirable conifer seedlings.
Application Methods
The method chosen should apply herbicide evenly for uniform weed control near planted seedlings. Tractor-mounted sprayers equipped to spray a strip of herbicide down the plantation row have had some success. When doing this, it is quite important that a wide enough strip be sprayed on each side of the planted row so that lateral roots do not draw down moisture supply too rapidly. In most situations, a strip at least 4 ft wide should be adequate for some habitat improvement for seedlings. If spot spraying, it is very important to use an even flat fan type of nozzle, such as a Spraying Systems 9502E. This will make a uniform swath about 5 ft wide when held 4 ft from the ground. As you pass over a seedling, a quick on–off will create square patches of treatment very quickly. Using a solid-cone nozzle in a circular motion around the tree risks excess dosage in the center. Treating spots up to 3 ft in diameter has not generally proven very satisfactory.
It is generally agreed that the most effective method of weed control for plantation establishment is broadcast application. While the cost of chemicals may be somewhat greater, the net cost per established tree should be somewhat lower with this method. Cost for most herbicide applications is a relatively small proportion of total plantation establishment cost. The greater the number of seedlings that can be established on a treated site, the smaller the unit cost per established seedling; hence the advantages are greatest for broadcast treatments in high-density plantings. For best yield, however, reforestation should seldom be done at spacings less than 10 x 10 ft.
Hand application equipment or aircraft are the only types of equipment suitable for application on rough terrain. It is estimated that 15% more chemical is needed for aerial treatments than for ground rigs to compensate for evaporation of fine droplets and loss of dust. Helicopters are the preferred aerial application equipment. They should be equipped for large droplet sizes and minimum drift potential.
Planting Techniques
In any plantation, but particularly on difficult sites, select the choicest quality planting stock of large vigorous seedlings. Machine planting and hand planting each has its advantages, but the benefits of machine planting are more striking when coupled with the use of herbicides. An ingenious operator can rig spray application equipment right on the planting machine so that the whole job is accomplished in one operation.
Removing all grass near planted trees exposes soil to the sun’s direct rays, raising surface temperatures enough to kill many young Douglas-fir and true fir seedlings. On many southern and southwestern exposures and on flat land in valley bottoms, the soil surface temperature may be responsible for just as much mortality as drought damage. If heat damage might occur, protect the seedling from direct contact with the hot soil at the ground surface. Use protective materials placed immediately around the root collar or stakes or shingles or similar types of materials that will shade the seedlings at the ground line. Ponderosa and lodgepole pine seedlings are more heat tolerant than other commonly used forest species; large seedlings of any species are more heat resistant than small trees, but any seedling must be given tender care in order to capitalize on weed control. 
   
Recommendations for Grass and Forbs
in Plantation Establishment

Conifer
planted	

Rainfall
zone (inches)	

Dominant weed type	Pounds of active ingredient or acid equivalent per acre, and season	
			atrazine	clopyralid1
	2,4-D2
	glyphosate3
	sulfometuron4
	hexazinone5
	
Douglas-fir, 
grand fir, noble fir, or spruces	50 +	Perennial grass-broadleaf mix	4 lb ai; April	2–6 oz ai	Up to 4 lb ae (D.-fir & spruces only)	1–3 lb ae	2–3 oz ai	1–2 lb ai	
	25–50	Annual grass, broadleaf	4 lb ai; March	2–6 oz ai	2 lb ae (up to 1 lb ae for true firs)	1–3 lb ae	2–3 oz ai	1–2 lb ai	
		Perennial grass, broadleaf	4 lb ai; March	2–6 oz ai	2 lb ae	1–3 lb ae	2–3 oz ai 	1–2 lb ai	
	Less than 25; high elev.	All	4 lb ai; fall		2 lb ae	1–3 lb ae	2–3 oz ai 	1–1.5 lb ai	
	Less than 25; low elev.	All	4 lb ai; Feb.		2 lb ae	1–3 lb ae	2–3 oz ai	1–2 lb ai	
All other	50 +	All	4 lb ai				2–4 oz ai	1–1.5 lb ai	
	Less than 50	All	4 lb ai				2–3 oz ai		
1 Clopyralid has activity on thistles. Use rates according to the Transline special local needs labels for Washington, Oregon, and Idaho.
2 Up to 2 lb/A of 2,4-D may be used over Douglas-fir seedlings without damage during the dormant season. Amine formulations are less harmful to conifers than esters but may less effectively control broadleaf weeds in early spring.
3 Glyphosate is somewhat selective on conifers during the entire period that trees show firmly prominent buds but is nonselective during the growing season. Selectivity decreases toward the end of winter. Damage just before bud burst occurs at 0.75 lb/A rate (1 quart/A). Glyphosate does not produce residual control when used alone. Apply when weeds are actively growing.
4 Apply preferably in fall to minimize injury to conifers; do not apply to newly planted seedlings.
5 Apply just before bud burst.