Weed Control in Nursery, Greenhouse, and Bulb Crops
Ed Peachey
Revised November 28, 2008

Site preparation  Field preparation begins several weeks before planting the nursery crop. To prepare the field for planting:
1.  Kill existing weeds with glyphosate.
2.  Allow 1 to 2 wk for the weeds to die, and then disk or till them into the soil.
3.  Wait another 2 to 3 wk to allow new weeds to germinate. This is a good time to apply preplant fertilizer and soil amendments.
4.  Before weeds grow more than 1 to 2 inches, disk or till the field again to kill germinated weeds and prepare the soil for planting.
5.  Plant the crop into weed-free soil.
Whether plowing, disking, or rototilling, till only as much as necessary to adequately prepare the soil for planting. Excessive tillage damages soil health. It can accelerate organic matter breakdown, reduce soil aggregates, increase the potential for soil compaction, reduce water percolation, and reduce soil oxygen levels. 
Repeated tillage has few short-term benefits for weed management. Some perennial weeds can be eradicated from fields with repeated tillage over a 1- to 2-yr period (tillage every 3 wk), but eliminating perennial weeds during the short field preparation process is unlikely. 
Repeated tillage does slowly reduce weed seed populations. However, most soils have an abundant depository of seeds, called the seed bank, and its depletion is a slow process. Excessive tillage during the short period of field preparation (4 to 6 wk) will not reduce weed seed numbers enough to justify the tractor fuel, time, and potential damage to soil structure. Furthermore, the planting process likely will bring buried seed up to the soil surface, thus partially offsetting any seed depletion benefits.
Ideally, plant immediately after final tillage. Recently tilled fields are free of weeds for a few days, an ideal situation for applying preemergence herbicides. Coordinate final tillage, planting, and first application of preemergence herbicide so all are within a 3- to 5‑day period.
NURSERY, GREENHOUSE, AND BULB CROPS—General Site Preparation
•  soil fumigants
See the current edition of the PNW Plant Disease Management Handbook for application details and list of approved materials.
•  glyphosate (numerous product names)
Rate  Consult labels
Time  Apply 1 to 4 wk before planting to allow time for chemical to move completely into the roots of actively growing weeds.
Remarks  Use lower rates for annual weeds; consult label for higher rates and application time for perennial weeds. Additional surfactant sometimes is helpful when weeds are less vigorous. Inhibits production of three amino acids and protein synthesis.
Caution  If repeat treatments are necessary within the crop, do not exceed 10.6 lb ai/A (10.6 quarts/A) in 1 yr. 
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
NURSERY—Site Preparation for Can Yards
•  woven polypropylene weed fabric
Many perennial and annual weeds can be controlled with proper construction of container areas and use of weed fabrics that prevent gravel from sinking into the soil.
•  dichlobenil (Casoron 4G) 
Rate  4 to 6 lb ai/A (100 to 150 lb/A Casoron)
Time  Apply to mineral soil and incorporate 4 to 6 inches deep before placing containers on treated area.
Remarks  Consult label for listed crops. Inhibits cell wall production.
Caution  Do not transplant into treated soil. Do not use in greenhouses. 
Site of action  Group 20: inhibits cell wall synthesis Site A 
Chemical family  Nitrile
•  prodiamine (Barricade 4L)
Rate  0.65 to 1.5 lb ai/A (21 to 48 fl oz/A Barricade 4L)
Time  Apply to soil, gravel, or other permeable surface before placing containers.
Caution  Minimize disturbance during hand-weeding to maintain herbicide layer. Apply in fall or spring before weeds germinate. 
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline

Weed Control in Container-grown Nursery Stock
Ed Peachey
Revised November 28, 2008

Weeds compete with commercial crops for nutrients, water, and light. Competition from weeds is particularly important in container crops due to the crops’ limited root volume. Weeds also harbor insects, disease organisms, and vertebrate pests. Marketable nursery crops must be free of weed, insect, and pathogen pests.
Effective weed management involves a combination of sanitary and cultural practices along with proper use of preemergence herbicides. For a more thorough discussion of weed management in container production, see Oregon State University Extension publication EM 8823, Weed Control in Container Crops.
Sanitation  Weed control in container production must be preventive. In field production, weeds often can be controlled efficiently after they germinate with directed sprays of herbicides or mechanical cultivation. In container crops where directed sprays are not feasible, there are few alternatives to costly hand-weeding to remove weed infestations. Thus a successful container weed management program should prevent weed germination.
The first step to effective weed management is sanitation. A common characteristic of weeds is their ability to produce prolific numbers of seed. Practices that minimize the number of weed seeds in the production system will improve weed control. The more weed seed allowed to contaminate containers, the higher the probability that weeds will germinate in areas where the herbicide barrier has been weakened or disrupted.
Herbicide use  For instructions on safe herbicide use, consult your local Extension agent, or refer to Oregon State University Extension publication EM 8850, Oregon Pesticide Safety Education Manual: A Guide to the Safe Use and Handling of Pesticides.
Maintaining a chemical barrier  Sanitation is the first step in effective weed control; proper herbicide use is the second. Herbicides form a chemical barrier over the container surface. Though each herbicide controls weeds differently, preemergence herbicides provide control at the point where germinating seeds emerge through the chemical barrier.
If the chemical barrier is incomplete, there will be a gap where weed seed can successfully germinate and grow. Several common practices can disrupt the chemical barrier, including but not limited to poking holes in the barrier with fingers or hands while moving containers, dropping containers, and container blow-over. Minimize all these activities to prevent disrupting the chemical barrier. Instructing the work crew is necessary because they typically are responsible for moving and working around the containers.
Pulling uncontrolled weeds also creates gaps in the chemical barrier. Pull weeds before they go to seed. Soon after removing weeds from an area, apply an herbicide to create a complete chemical barrier and prevent germination of more weeds.
Selecting preemergence herbicides  Preemergence herbicides are applied before weeds emerge, to prevent weed growth. This is in contrast to postemergence herbicides, which kill weeds after they have emerged and are actively growing. Base your selection of herbicides primarily on three criteria: the crop to which the herbicide will be applied, weed species to be controlled, and herbicide solubility. Other considerations include the importance of rotating herbicide chemistry and the choice of granular versus spray-applied herbicides (for more information, see Oregon State University Extension publication EM 8823, Weed Control in Container Crops.
Crop tolerance of herbicides  Selecting an herbicide based on the crop being grown is critical. Every herbicide label describes how the product should be used and to which plants it can be applied safely, based on experimental tests. Chemical manufacturers make every effort to ensure that plants listed on labels can be treated safely. However, not every environmental or cultural situation can be predicted or accounted for when testing products. Therefore, before using a new herbicide or using a familiar herbicide on a new crop, conduct a small trial to ensure the plant and herbicide are compatible under conditions specific to your production system (regardless of whether or not the plant is listed on the label). 
Apply herbicides before weed seed germinates  The most important rule for herbicide application timing, the rule that trumps all others, is that preemergence herbicides work best if applied before weed seed germinates. Preemergence herbicides will not control weed plants present at the time of application. Two notable exceptions are spray-applied Goal (oxyfluorfen)  and SureGuard (flumioxazin) , will kill weeds less than 4 inches tall. However, they are limited to field use and some container-grown conifers.
Existing weeds in containers must be hand-weeded before application. Weed plants present at the time of herbicide application will continue to grow and produce seed, thus perpetuating the problem. Applying preemergence herbicides to containers where weeds are growing is a waste of the herbicide and labor needed to apply it (a costly mistake).
Herbicides at potting  Herbicides can and should be applied soon after potting. When potting liners or shifting plants into larger containers, irrigate two or three times before applying an herbicide in order to settle the substrate (media). For best results, apply herbicides after recently potted crops have received about 1 inch of irrigation or precipitation. When using certain herbicides, wait 2 to 4 wk before application when potting bareroot plants into containers. (Check labels for specific instructions.)
If herbicides are applied immediately after potting, before settling, macropores in the substrate can allow herbicides to channel and make contact with plant roots, causing injury or stunting. If herbicides are withheld for too long after potting, weed seed may germinate.
Weed control is most effective when herbicides are applied at the proper rate and the proper time and in conjunction with good sanitation.
CONTAINER-GROWN NURSERY STOCK—Weed Control within Containers
•  covers or mulches designed to prevent weed growth with air pruning
Rate  Place 0.5 inch of nondecomposable mulch such as hazelnut shells, sawdust, coco-fiber disks, geotextile disks, or any number of commercially available plastic disks to prevent weeds from germinating and establishing in wet–dry cycles.
Time  During container filling.
Remarks  Filling the container with a porous mulch that dries on the container rim prevents weeds from establishing by wetting and drying cycles. This technique requires retooling during the planting operation but can suppress weeds throughout the life cycle of the crop.
Caution  Avoid products, including coarse or rigid materials, that might damage the stem of the crops.
•  oxadiazon (Ronstar G)
Rate  2 to 4 lb ai/A (100 to 200 lb/A Ronstar)
Time  Apply uniformly with granular applicator any time to weed-free containers when plants are dry. Irrigate with 0.25 to 0.33 inch water immediately after application.
Remarks  Pink family weeds (chickweed, mouseear chickweed, and pearlwort) are resistant. Controls weed seedlings by contact action during emergence.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  Oxadiazole
•  napropamide (Devrinol 2G or Devrinol 50DF)
Rate  4 ai/A (8 lb/A Devrinol 50DF).
Time  Apply any time to weed-free containers and irrigate immediately with 0.5 inch water. 
Remarks  Use higher rates on severe weed infestations or if broadleaf weeds predominate. Inhibits root growth.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Acetamide
•  oryzalin (Surflan AS)
Rate  2 to 4 lb ai/A (2 to 4 quarts/A Surflan AS)
Time  Apply to established plants only in weed-free containers and irrigate as soon as possible with 0.5 inch water.
Remarks  Establish rooted liners in containers at least 2 wk before treatment. Inhibits cell division or mitosis, primarily in roots.
Caution  Do not apply again within 90 days. 
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  prodiamine (Barricade 4L or RegalKade G)
Rate 0.65 to 1.5 lb ai/A (21 to 48 fl oz/A Barricade 4L) 
Time  Apply to weed-free site.
Remarks  Follow with 0.5 inch rain or irrigation.
Caution  Do not exceed maximum rate listed on label in a 12-mo period.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  isoxaben (Gallery 75 DF)
Rate  0.495 to 0.99 lb ai/A (0.66 to 1.33 lb/A)
Time  Apply to weed-free soil.
Remarks  Identify weeds and adjust rates according to charts on label. Chemical stability is adequate when left on soil surface for 21 days.
Caution  Do not apply to newly transplanted crops until medium is settled (two to three irrigations).
Site of action  Group 21: inhibits cell wall synthesis Site B
Chemical family  Benzamide  
•  flumioxazin (SureGuard 51WDG)
Rate  0.25 to 0.38 lb ai/A (8 to 12 oz/A SureGuard)
Time  Apply  to weed-free containers or containers with small weeds (less than 2 inches tall). Apply to established and dormant conifers only (see label for list of approved species).
Remarks  Has some postemergence activity on small weeds. Preemergence control is better if applied to weed-free containers. Payload is similar to SureGuard and is labeled for use to maintain bare ground and noncrop areas.
Caution  Do not apply over the top of deciduous or broadleaf evergreen crops.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  N-phenylphthalimide
•  flumioxazin (Broadstar 0.25G)
Rate  0.375 lb ai/A (150 lb/A Broadstar) 
Time  Apply to weed-free containers.
Caution  Foliage of desirable crops must be dry at the time of application. Wet foliage will trap granules on the leaf surface, disperse the herbicide, and burn the foliage.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  N-phenylphthalimide
•  isoxaben + trifluralin (Snapshot 2.5TG) 
Rate  2.5 to 5 lb ai/A (100 to 200 lb/A Snapshot), depending on prevalent weed species; consult label
Time  Apply to weed-free soil.
Remarks  Soil must be settled with water and free of cracks after transplanting. Activate within 3 days using 0.5 inch of water before weeds begin to emerge. See label for repeat treatments.
Caution  Do not apply to unrooted liners or cuttings, bedding plants, or newly planted ground cover.
Site of action  (isoxaben) Group 21: inhibits cell wall synthesis Site B; (trifluralin) Group 3: microtubule assembly inhibitor
Chemical family  (isoxaben) benzamide; (trifluralin) dinitroaniline
•  isoxaben + trifluralin + oxyfluorfen (Showcase)
Rate  2.5 to 5 lb ai/A (100 to 200 lb/A) 
Time  Apply to weed free soil 
Remarks  Soil must be settled with water and free of cracks after transplanting. Activate within 3 days using 0.5 inch of water before weeds begin to emerge. See label for repeat treatments. 
Caution  Do not apply to unrooted liners or cuttings. 
Site of action  (isoxaben) Group 21: inhibits cell wall synthesis Site B; (trifluralin) Group 3: microtubule assembly inhibitor 
Chemical family  (isoxaben): benzamide; (trifluralin) dinitroaniline: (oxyfluorfen) diphenylether 
•  dithiopyr (Dimension) 
Rate  0.5 lb ai/A (2 quarts/A)
Time  Apply to bare ground, or containers before target weeds germinate. 
Remarks  For best weed control, apply to soil that is free of clods, weeds, and debris such as leaves. Requires activation with 0.5 inch or more of rain or irrigation. 
Site of action  Group 3: microtubule assembly inhibitor 
Chemical family  Pyridine
•  pendimethalin (Corral 2.68G, Pendulum WDG, or Pendulum 2G)
Rate  1.5 to 2 lb ai/A (75 to 100 lb/A Pendulum 2G)
Time  Apply only to dry crop foliage, either before weed seeds germinate or after completely removing weeds.
Remarks  Water immediately with 0.5 inch to activate herbicide. For container plants, delay first application to bareroot liners for 2 to 4 wk. Inhibits mitosis in roots and shoots.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
• S-metolachlor (Pennant Magnum)
Rate  1.24 to 2.48 lb ai/A (1.3 to 2.6 pints/A Pennant Magnum)
Time  Apply any time to weed-free containers for ornamentals transplanted at least 5 days.
Remarks  Direct spray toward base of ornamental plant to avoid possible injury. Activate herbicide with brief irrigation. Use lower rates on porous media and reduced weed infestations. Provides approximately 60-day control, less under very wet conditions. Inhibits seedling roots and/or shoots.
Caution  Do not exceed 4 lb ai/A per year or per crop cycle (whichever is less), in a given area. 
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  oxyfluorfen (Goal 2XL)
conifers and selected deciduous trees only
Rate  0.5 to 1.5 lb ai/A, (2 to 6 pints/A Goal 2XL) depending on use; check label
Time  Apply after transplanting to dormant conifer stock and irrigate with 0.5 to 0.75 inch water or rain for preemergence control of annual grasses and broadleaf weeds.
Remarks  Postemergence applications can control susceptible broadleaf weeds up to 4 inches tall. Acts as contact-type herbicide.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  Diphenylether
•  benefin + oryzalin (XL 2G)
Rate  4 to 6 lb ai/A (200 to 300 lb/A XL 2G)
Time  Apply before weeds germinate; incorporate immediately with shallow cultivation (1 to 2 inches) or overhead water. 
Remarks  Application equipment must be precisely calibrated, preferably at half rates, to enable two perpendicular passes for more accuracy. Inhibits cell division or mitosis, primarily in roots.
Site of action  (both) Group 3: microtubule assembly inhibitor
Chemical family  (both) dinitroaniline
•  oxyfluorfen + pendimethalin (OH2 Ornamental Herbicide) 
Rate  100 lb/A (2% + 1% formulation, respectively)
Time  Apply product uniformly using a rotary or drop-type granular spreader either after transplanting potted liners (wait until after two to three irrigations to allow media to settle) or 3 to 4 wk after planting bareroot liners but before weeds emerge.
Remarks  Requires 0.5 to 1 inch water to activate immediately after application. Acts as contact-type herbicide and inhibits mitosis in roots and shoots, respectively.
Site of action  (oxyfluorfen) Group 14: protoporphyrinogen oxidase inhibitor; (pendimethalin) Group 3: microtubule assembly inhibitor
Chemical family  (oxyfluorfen) diphenylether; (pendimethalin) dinitroaniline
•  oryzalin + oxyfluorfen (Rout)
Rate  100 lb/A (2% + 1% formulation, respectively)
Time  Apply product uniformly after a 0.5-inch irrigation for potted liners or 3 wk after potting bareroot liners.
Remarks  Irrigate with 0.5 inch water immediately after application. Note all precautions on label. Acts as contact-type herbicide and inhibits cell division or mitosis in roots and shoots, respectively.
Caution  Do not apply to wet foliage or plants with whorls. 
Site of action  (oryzalin) Group 3: microtubule assembly inhibitor; (oxyfluorfen) Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  (oryzalin) dinitroaniline; (oxyfluorfen) diphenylether
•  napropamide + oxadiazon (Pre Pair)
Rate  100 to 150 lb/A (4% + 2% formulation, respectively)
Time  Postplant after soil settles from first irrigation but before weed seeds germinate.
Remarks  Note all precautions, including sensitive crops. Does not control emerged weeds. 
Site of action  (napropamide) Group 15: inhibits very long chain fatty acid synthesis; (oxadiazon) Group 14: protoporphyrinogen oxidase inhibitor
Chemical family (napropamide) acetamide; (oxadiazon) oxadiazole
•  oxyfluorfen + oxadiazon (RegalO-O Herbicide)
Rate  100 lb/A
Time  Apply uniformly before weeds begin to germinate and emerge; follow with 0.5 inch irrigation or rain to activate herbicide.
Remarks  Avoid application to wet foliage.
Site of action  (both) Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  (oxyfluorfen) diphenylether; (oxadiazon) oxadiazole
•  isoxaben + trifluralin (Snapshot 2.5TG)
Rate  2.5 to 5 lb ai/A (100 to 200 lb/A)
Time  Apply to weed free soil
Remarks  Soil must be settled with water and free of cracks after transplanting. Activate within 3 days using 0.5 inch of water before weeds begin to emerge. See label for repeat treatments.
Caution  Do not apply to unrooted liners or cuttings.
Site of action  (isoxaben) Group 21: inhibits cell wall synthesis Site B; (trifluralin) Group 3: microtubule assembly inhibitor
Chemical family  (isoxaben): benzamide; (trifluralin) dinitroaniline
•  oxadiazon + prodiamine (RegalStar G)
Rate  200 lb/A
Time  Apply uniformly before weeds begin germination and emergence following newly transplanted or established nursery crops. 
Remarks  Do not apply to wet foliage or inside greenhouses.
Site of action  (oxadiazon) Group 14: protoporphyrinogen oxidase inhibitor; (prodiamine) Group 3: microtubule assembly inhibitor
Chemical family  (oxadiazon) oxadiazole; (prodiamine) dinitroaniline
•  fluazifop (Fusilade II or Ornamec Over-the-Top)  
Rate  0.25 to 0.375 lb ai/A (1 to 1.5 pints/A Fusilade II)
Time  Apply to actively growing grasses or within 7 days after irrigation with 0.25% nonionic surfactant. 
Remarks  Applied over the top of nursery plants for selective postemergence grass control. Identify grasses and adjust rates depending on susceptibility and stage of weed growth according to label instructions. Note lists of ornamentals and associated instructions regarding topical versus directed sprays. Results often are erratic on grasses stressed from lack of vigor, drought, high temperature, or low fertility. More mature grasses and quackgrass can be controlled but may require two applications. Annual bluegrass and all fine fescues resist treatment. Inhibits fatty acid production, cell membranes, and new growth.
Caution  Do not tank-mix with other pesticides or apply within 5 days of other pesticides. Grazing is prohibited. 
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Aryloxyphenoxy propionate
•  fenoxaprop (Acclaim Extra)
Rate  0.058 to 0.174 lb ai/A (13 to 39 fl oz/A or 13 to 39 fl oz/1,000 sq ft)
Time  Adjust rates depending on number of grass tillers (see label).
Remarks  For selective postemergence grass control. Thoroughly cover actively growing, susceptible grasses. Repeat after grass begins active growth, but do not exceed 120 fl oz/A per season. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Aryloxyphenoxy propionate
•  sethoxydim (Segment or Vantage; registered only in Washington)
Rate  0.28 to 0.47 lb ai/A (36 to 60 fl oz/A)
Time  Apply at optimum growth stage as on label.
Remarks  For selective postemergence grass control. Identify susceptible grasses. Control often is erratic if grasses are stunted or stressed from drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues, but quackgrass can be suppressed. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  clethodim (Envoy)
Rate  0.095 to 0.25 lb ai/A (13 to 34 fl oz/A)
Time  For selective postemergence grass control. Apply postemergence to actively growing annual or perennial grasses as listed on label. Consider environmental and plant growth conditions that affect leaf uptake; see label for guidelines.
Caution  Do not exceed 68 fl oz/A per season. 
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
CONTAINER-GROWN NURSERY STOCK—Container Growing Areas
•  oryzalin (Surflan)
Rate  2 to 4 lb ai/A 
Time  Apply any time to weed-free area beneath and around container-grown stock listed on label. 
Remarks  Inhibits cell division or mitosis primarily in roots. Roots growing from pot drainage holes are pruned without crop injury because the herbicide does not translocate upward in the plant.
Site of action Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  dichlobenil (Casoron 4G)
Rate  4 to 8 lb ai/A; 10 lb ai/A for nutsedge (100 to 200 lb/A Casoron; 250 lb/A Casoron for nutsedge)
Time  Treat area before containers are set in midwinter when temperatures are cold and rain is expected immediately after application to activate herbicide and prevent loss by volatility. 
Site of action  Group 20: inhibits cell wall synthesis Site A 
Chemical family  Nitrile 
•  glufosinate ammonium (Finale)
spot or directed spray only
Rate  1 to 1.5 lb ai/A (4 to 6 quarts/A Finale)
Time  Apply around containers to thoroughly cover actively growing weeds.
Remarks  A postemergence, partially systemic herbicide. Avoid all contact with foliage and green bark of desirable crops.
Site of action  Group 10: glutamine synthetase inhibitor
Chemical family  Phosphinic acid
•  pelargonic acid (Scythe)
Rate  3 to 5% solution to control annual weeds, mosses and cryptogams; 5 to 7% solution for burndown of perennial herbaceous plants; 7 to 10% solution for maximum vegetative burndown, edging, or foliar trimming.
Time  Apply to thoroughly wet weed foliage as a directed spray around containers. Most effective when temperature is above 65°F.
Remarks  Avoid contact with desirable vegetation. Disrupts cell membranes, causing leakage and symptoms of leaf burn. 
Site of action  Group 26: unknown
Chemical family  Carboxylic acid

Weed Control in Field-grown Nursery Stock and Holly
Ed Peachey
Revised November 21, 2008
Weeds compete with newly planted nursery stock. Deep-rooted perennial weeds can reduce vigor and render a mature product unsaleable due to laws on transporting noxious weeds. Consequently, weeds are controlled with herbicides either applied broadcast in closely spaced crops, or within the tree or shrub row for wider spaced crops with alleys being mowed or flailed.
Weed shifts  Repeated use of simazine was first demonstrated in nurseries to cause a shift within a natural population of common groundsel to a resistant or tolerant biotype. Routine cultural practices also cause such a weed shift. Examples include prostrate weeds that tolerate flailing, deep-rooted or easily spread perennials that tolerate cultivation, and weeds that resist repeated applications of the same or similar herbicide treatments.
Preventing weed shifts  Weeds that survive cultivation, mowing or flailing, specific herbicide treatments, or other routine cultural practices must be eliminated before the tolerant species or biotypes become established. Combine a variety of weed control practices or treatments; rotate fields, cultural practices, and herbicides; and spot treat with a hoe or registered herbicide when the weed first appears. Also, clean equipment when moving from an infested field.
Sod covers  In specimen tree plantings, manage either native or planted grasses in row middles to reduce soil erosion and improve traffic conditions during wet weather. In addition, soil moisture and nutrient retention are improved along with increased water infiltration rates for many sods. New sod varieties including dwarf cultivars that respond to minimal management practices such as drought, low fertility, or sublethal rates of postemergence herbicides are being introduced into various horticultural cropping systems. Consult your local Extension agent or request recent information about living mulches and their management.
Managing weedy vegetation  Successful weed control in nurseries requires a comprehensive, year-round approach that uses and alternates a combination of weed control practices over several years. Developing these strategies requires knowledge of each weed and weed control practice. Weeds must be identified and information gathered about the effectiveness of each weed control practice. Consider costs and select herbicide combinations that may be applied together or in split applications that control all weeds present in the nursery. Note the action of each herbicide or how the chemical works in the plant. Then tank-mix and alternate use of these products to reduce the chance of developing resistant species or biotypes. Often a combination of mechanical, herbicidal, and sometimes hand-removal or spot-treatment with herbicide sprays or wipers will provide the most effective year-round control.
Soil-active herbicides  Persistent, soil-applied herbicides can be applied to weed-free soil during winter when rain will activate the chemical, or some compounds may be applied throughout the year. Apply lower rates on sandy soils having lower clay, organic matter, or cation exchange capacities. Existing vegetation can be controlled by mixing a postemergence contact or translocated herbicide. Consult label for listed species and duration of expected control.
Postemergence herbicides  In nursery production, postemergence weed control requires precision. Postemergence treatments either selectively control susceptible weeds or are applied with selective equipment.
Frequent scouting to identify susceptible weeds and the correct stage of weed growth must be combined with appropriate weather conditions and labeled spray additives to maximize control. Consult labels for numerous precautions or information about crop or cultivar tolerances. Due to the multitude of nursery crops, always verify selectivity on a few plants before treating the entire block or field.
Note  Herbicides must be applied at exactly the correct rate and time to selectively control weed growth with minimal chance for injury to nursery crops. Obtain more consistent results by reading the herbicide label and other information about the proper application and timing of each herbicide. Suggested rates listed in this guide are stated as pounds active ingredient per acre (lb ai/A) or pounds acid equivalent per acre (lb ae/A). For band applications under tree rows, reduce quantity of herbicide applied proportionally to the area within the row actually sprayed. 
FIELD-GROWN NURSERY STOCK AND HOLLY—New and Established Plantings
•  EPTC (Eptam 7E or Eptam 20G) 
Rate  Consult labels
Time  Apply 2 wk before transplanting balled and canned stock (only) or any time after transplanting or growth on established plants begins in spring. 
Remarks  Use lower rate and incorporate with nursery cultivator or rototillers to 3 inches for annual weeds and higher rates to 6 inches for perennial weeds. Inhibits shoots of emerging seedlings.
Site of action  Group 8: lipid synthesis inhibitor but not an ACCase inhibitor
Chemical family  Thiocarbamate
•  dithiopyr (Dimension)
Rate  0.5 lb ai/A
Time  Apply to bare ground, before target weeds germinate.
Remarks  For best weed control, apply to soil that is free of clods, weeds, and debris such as leaves. 
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Pyridine
•  trifluralin (Treflan 5G)
Rate  4 lb ai/A
Time  Apply to established nursery crops before weeds germinate. Incorporate with 0.5 inch of irrigation or rain within 3 days of application. Inhibits cell division or mitosis, both in roots and shoots.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  oxadiazon (Ronstar G or Ronstar 50WSP)
Rate  2 to 4 lb ai/A (100 to 200 lb/A Ronstar G)
Time  Apply uniformly with granular applicator any time to weed-free soil and when plants are dry.
Remarks  Irrigate with 0.25 to 0.33 inch water immediately after applying; do not incorporate mechanically. Weeds in the pink family (chickweed, mouseear chickweed, pearlwort) are resistant. Controls weed seedlings by contact action during emergence.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  Oxadiazole
•  flumioxazin (SureGuard 51WDG)
Rate  0.25 to 0.38 lb ai/A (8 to 12 oz/A SureGuard)
Time  Apply to weed-free soil. Kills existing annual weeds postemergence if weeds are less than 2 inches. Apply to established and dormant conifers.
Remarks  Can be used safely on established and dormant conifers. Also can be applied to established deciduous crops (check label) with directed sprays as long as contact with foliage and green bark is avoided. Injury to linden (Tilia spp.), which has a thin, green bark when young, has been noted in several Oregon nurseries. Payload is similar to SureGuard and is labeled for use to maintain bare ground and noncrop areas.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  N-phenylphthalimide
•  flumioxazin (BroadStar 0.25G)
Rate  0.375 lb ai/A (150 lb/A BroadStar)
Time  Apply to weed-free containers.
Caution  Foliage of desirable crops must be dry at the time of application. Wet foliage will trap granules on leaf surface, disperse herbicide, and burn foliage.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  N-phenylphthalimide
•  napropamide (Devrinol 2G or Devrinol 50DF)
Rate  4 lb ai/A (8 lb/A Devrinol 50DF)
Time  Consult label for crops listed. Apply November to February and irrigate if no rain falls within 2 to 3 days; or apply March through October and irrigate within 24 hours to wet soil 2 to 4 inches deep.
Remarks  Shallow mechanical incorporation improves performance. Use higher rates if weed infestations are severe or broadleaf weeds predominate. Inhibits root growth.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Acetamide
•  oryzalin (Surflan AS)
Rate  2 to 4 lb ai/A (2 to 4 quarts/A Surflan AS)
Time  Apply any time to bare soil. Activate within 21 days with 0.5 inch water. Wait at least 90 days before repeating application. Apply only to established plantings. 
Remarks Inhibits cell division or mitosis, primarily in roots.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  pendimethalin (Pendulum 2G, Pendulum WDG, or Corral 2.68G)
Rate  1.5 to 2 lb ai/A (75 to 100 lb/A Pendulum 2G)
Time  Apply at planting or before weed seed germinates. Soil should be loose and free of established weeds.
Remarks  Water within a few days to activate herbicide before weeds emerge. Inhibits mitosis in roots and shoots.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  prodiamine (Barricade 4L or RegalKade)
Rate  0.65 to 1.5 lb ai/A (21 to 48 fl oz/A Barricade)
Time  Apply to weed-free site.
Remarks  Follow with 0.5 inch rain or irrigation or shallow incorporation.
Caution  Do not exceed maximum rate on label in a 12-mo period. Do not apply to recently planted red maple (Acer rubrum) liners; this species is not labeled, and severe girdling has been observed in several Oregon nurseries.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  isoxaben (Gallery 75 DF)
Rate  0.495 to 0.99 lb ai/A (0.66 to 1.33 lb/A)
Time  Apply in late summer to early fall, in early spring, or immediately after cultivation. Apply to debris-free soil surface.
Remarks  Identify weeds and adjust rates as on charts on label. Activate with 0.5 inch water or shallow cultivation before weeds emerge. Chemical is stable enough when left on soil surface for 21 days.
Caution  Do not apply to newly transplanted crops until media settle.
Site of action  Group 21: inhibits cell wall synthesis Site B
Chemical family  Benzamide  
•  isoxaben + trifluralin (Snapshot 2.5TG) 
Rate  2.5 to 5 lb ai/A (100 to 200 lb Snapshot/A)
Time  Apply to weed-free and debris-free soil. 
Remarks  Soil must be settled with water and free of cracks after transplanting. Activate within 3 days using 0.5 inch of water or shallow cultivation before weeds begin to emerge. Follow label instructions for repeat treatments.
Caution  Do not apply to unrooted liners or cuttings, bedding plants, or new-planted ground cover.
Site of action  (isoxaben) Group 21: inhibits cell wall synthesis Site B; (trifluralin) Group 3: microtubule assembly inhibitor
Chemical family  (isoxaben) benzamide; (trifluralin) dinitroaniline
•  alachlor (Microtech)
yew and juniper only
Rate  4 lb ai/A (4 quarts/A)
Time  Directed spray after transplanting, or to established plantings prior to weed emergence.
Caution  A restricted-use herbicide. Do not apply to wet foliage. Maximum use rate is 4 lb ai per year. Do not use on seedbeds or unrooted cuttings or before transplanting. Inhibits seedling roots and/or shoots.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  S-metolachlor (Pennant Magnum)
Rate  1.24 to 2.48 lb ai/A (1.3 to 2.6 pints/A Pennant Magnum)
Time  Apply any time to weed-free soil as a spray directed to base of ornamentals transplanted at least 10 days. 
Remarks  Activate herbicide with light irrigation. Use lower rates on sandy soils and reduced weed infestations. Gives about 60 days control, less under very wet conditions. Suppresses yellow nutsedge when applied preemergence and activated with adequate water. 
Caution  Do not use on seedbeds or unrooted cuttings. Inhibits seedling roots and/or shoots.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  DCPA (Dacthal)
Rate  10.5 to 12 lb ai/A
Time  Apply any time to weed-free soil; activate with ample irrigation 3 to 5 days after treatment.
Remarks  Applications west of Cascades usually perform poorly. In other areas, can be applied immediately after planting liners. Inhibits cell division or mitosis in roots and shoots.
Caution  Do not use on seedbeds. 
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Phthalic acid
•  pronamide  (Kerb)
established stock only
Rate  1 to 2 lb ai/A
Time  Apply in fall before leaves drop or soil freezes. Or, apply from early to midwinter west of Cascades to soil relatively free of plant residues.
Remarks  Requires soil moisture from rain or irrigation to activate; do not incorporate mechanically. Use lower rates for annual grasses and light-texture soils; higher rates for perennial grasses and heavier soils. Control of established grasses is slow. Degraded by microorganisms in warmer weather. Use on nursery stock established at least 1 yr and seedlings that are at least 1 yr old. Inhibits root growth.
Caution  A restricted-use pesticide.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Benzamide
•  dichlobenil (Casoron 4G)
established stock only
Rate  4 to 8 lb ai/A (100 to 200 lb/A granular product)
Time  Apply midwinter immediately before a cold rain to reduce volatility and to enhance weed suppression.
Remarks  Weigh and distribute exact quantities over precisely measured areas to ensure accurate applications. Avoid applying near tree trunks to reduce possible girdling.
Caution  Do not apply for 6 mo while roots develop on liners, or until 4 wk after transplanting stock. Oregon results over 9 yr suggest that perennial weeds can be suppressed with 4-, 3-, and 2-lb ai/A rates applied during 3 consecutive years. Grazing livestock is prohibited. Inhibits cellulose and cell wall formation.
Site of action  Group 20: inhibits cell wall synthesis Site A 
Chemical family  Nitrile
FIELD-GROWN NURSERY STOCK—New and Established Plantings
•  norflurazon (Predict)
established stock only
Rate  3 lb/A
Time  Apply in fall or spring to bare soil after nursery crops are established.
Remarks  Rain must be adequate before weeds begin to emerge. Read label thoroughly about site, soil, crop rotation, and mixing precautions. Inhibits yellow pigment formation, bleaching green chlorophyll.
Site of action  Group 12: bleaching; inhibits carotenoid biosynthesis
Chemical family  Pyridazinone
•  simazine (Simazine 4L and others)
established stock only
Rate  2 to 3 lb ai/A
Time  Apply at least 1 yr after transplanting to weed-free soil and activate with rain or sprinkler irrigation. 
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazine
•  atrazine
established Douglas-fir, fir, Sitka spruce, and pine only
Rate  2 to 4 lb ai/A
Time  Apply October through March when trees are dormant.
Remarks  Can be applied after small weeds emerge. Requires rain or sprinkler irrigation to activate. Apply only once per year.
Caution  A restricted-use pesticide.
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazine
•  oxyfluorfen (Goaltender) 
Rate  0.5 to 2 lb ai/A (1 to 4 pints/A)
Time  Apply to deciduous, field-grown shade trees listed on label; direct the applications toward the soil and tree base. Apply to 2-0 conifers in winter dormancy fall through winter. After transplanting, irrigate with 0.5 to 0.75 inch water or rain for preemergence control of annual grass and broadleaf weeds. Do not exceed 2 lb ai/A in 1 yr. 
Remarks  Postemergence applications control susceptible broadleaf weeds up to 4 inches tall. Goaltender is a contact-type herbicide with some soil residual activity. 
Site of action  Group 14: protoporphyrinogen oxidase inhibitor 
Chemical family  Diphenylether 
•  benefin + oryzalin (XL 2G)
Rate  4 to 6 lb ai/A (200 to 300 lb/A XL 2G)
Time  Apply before weeds germinate. Incorporate immediately with shallow cultivation (1 to 2 inches) or overhead water.
Remarks  Precisely calibrate application equipment, preferably at half rates, to enable two perpendicular passes for more accuracy. Inhibits cell division or mitosis, primarily in roots.
Site of action  (both) Group 3: microtubule assembly inhibitor
Chemical family  (both) dinitroaniline
•  oxyfluorfen + pendimethalin (OH2 Ornamental Herbicide) 
Rate  100 lb/A (2% + 1% formulation, respectively)
Time  Apply uniformly using a rotary or drop-type spreader either immediately after transplanting new stock or to weed-free soil.
Remarks  Requires 0.5 to 1 inch water immediately after application to activate and to wash product from leaves.
Caution  Do not incorporate mechanically. Respectively, a contact-type herbicide and an herbicide that inhibits cell division or mitosis in roots and shoots.
Site of action  (oxyfluorfen) Group 14: protoporphyrinogen oxidase inhibitor; (pendimethalin) Group 3: microtubule assembly inhibitor
Chemical family  (oxyfluorfen) diphenylether; (pendimethalin) dinitroaniline
•  oxyfluorfen + oryzalin (Rout)
Rate  100 lb/A (2% + 1% formulation, respectively)
Time  Apply uniformly either in spring before weeds germinate or to weed-free soil.
Remarks  Requires 0.5 inch water immediately after application to activate and to wash product from leaves. A contact-type herbicide; inhibits cell division or mitosis in roots and shoots, respectively.
Caution  Do not apply to wet foliage or plants with whorls.
Site of action  (oxyfluorfen) Group 14: protoporphyrinogen oxidase inhibitor; (oryzalin) Group 3: microtubule assembly inhibitor
Chemical family  (oxyfluorfen) diphenylether; (oryzalin) dinitroaniline
•  napropamide + oxadiazon (PrePair)
Rate  6 to 9 lb ai/A (100 to 150 lb/A Pre Pair)
Time  Apply uniformly any time to weed-free surface.
Remarks  Newly planted stock can be treated when soil settles after first irrigation. Activate with overhead irrigation.
Caution  Do not apply in greenhouses or to wet foliage.
Site of action  (napropamide) Group 15: inhibits very long chain fatty acid synthesis; (oxadiazon) Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  (napropamide) acetamide; (oxadiazon) oxadiazole
•  oxyfluorfen + oxadiazon (RegalO-O Herbicide)
Rate  100 lb/A
Time  Apply uniformly before weeds begin to germinate and emerge; follow with 0.5 inch irrigation or rain to activate herbicide.
Remarks  Avoid application to wet foliage.
Site of action  (both) Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  (oxyfluorfen) diphenylether; (oxadiazon) oxadiazole
•  oxadiazon + prodiamine (RegalStar G)
Rate  200 lb/A
Time  Apply uniformly before weeds begin to germinate and emerge following newly transplanted or established nursery crops.
Remarks  Avoid application to wet foliage.
Caution  Do not apply in greenhouses.
Site of action  (oxadiazon) Group 14: protoporphyrinogen oxidase inhibitor; (prodiamine) Group 3: microtubule assembly inhibitor
Chemical family  (oxadiazon) oxadiazole; (prodiamine) dinitroaniline
•  oxyfluorfen (Goal)
Rate  0.5 to 2 lb ai/A
Time  Apply to deciduous, field-grown shade trees listed on label; direct the applications toward the soil and tree base. Apply to 2-0 conifers in winter dormancy fall through winter. After transplanting, irrigate with 0.5 to 0.75 inch water or rain for preemergence control of annual grass and broadleaf weeds.
Remarks  Postemergence applications control susceptible broadleaf weeds up to 4 inches tall. A contact-type herbicide with some soil residual activity.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  Diphenylether
•  bentazon (Basagran T/O)
Rate  0.75 to 1 lb ai/A
Time  Postemergence control of broadleaf weeds, Canada thistle, yellow nutsedge, and musk thistle. 
Remarks  Direct sprays toward actively growing weed foliage at weed size described on label. Add 2 pints/A crop oil concentrate to enhance activity (see label). Two treatments 7 to 10 days apart may be required for Canada thistle or yellow nutsedge. Temperatures below 55°F, drought, or rain within 8 hr will reduce activity. Inhibits photosynthesis.
Caution  Do not apply within 1 yr of harvest or exceed 2 lb ai/A per season. Livestock grazing within treated area or feeding treated hay is prohibited. Do not use on sycamore or rhododendron. 
Site of action  Group 6: photosystem II inhibitor
Chemical family  Benzothiadiazole 
•  glyphosate (numerous product names)
Rate  Spray—consult label
Time  Apply as a directed spray toward base of tree when weeds are actively growing or moving sugars to roots.
Remarks  Inhibits production of three amino acids and protein synthesis.
Caution  Do not spray green bark, foliage, or root suckers. If repeat applications are necessary, do not exceed a total of 10.6 lb ai/A (10.6 quarts/A) in 1 yr.
Remarks  Consult label about rate and time of application, especially perennial weeds.
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
•  glyphosate (several products)
Rate  Wiper—33% solution
Time  Mix 1 gal product to 2 gal water and wipe weeds, avoiding contact with desirable vegetation. 
Remarks  In severe infestations, reduce equipment ground speed or apply in two directions to ensure contact with wiper. (See remarks above.)
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
•  glufosinate ammonium  (Finale)
spot or directed spray only
Rate  1 to 1.5 lb ai/A (4 to 6 quarts Finale/A)
Time  Apply to thoroughly cover actively growing weeds.
Remarks  Avoid all contact with desirable foliage and green bark.
Site of action  Group 10: glutamine synthase inhibitor
Chemical family  Phosphinic acid
•  pelargonic acid (Scythe)
for nursery trees and shrubs
Rate  3 to 5% solution to control annual weeds, mosses and cryptogams; 5 to 7% solution to burn down perennial herbaceous plants
Time  Apply to thoroughly wet foliage, either broadcast to noncrop area or before ornamental crop emerges; or spot treat and trim around ornamentals, trees, flower beds, paths, etc. Most effective when temperature is above 65°F.
Remarks  Controls small, actively growing weeds and weakens established weeds by removing susceptible vegetation. Disrupts cell membranes, causing leakage and symptoms of leaf burn. 
Site of action  Group 26: unknown
Chemical family  Carboxylic acid
•  paraquat (Gramoxone Inteon or Gramoxone Max) 
established stock only
Rate  Consult labels; formulations differ
Time  Apply as a directed or directed-shielded application when weeds are small (6 inches or less) and actively growing.
Remarks  Add a nonionic surfactant or crop oil concentrate according to label specifications taking care to avoid anionic formulations that react in the tank to form insoluble precipitates. Avoid contact with stems or leaves of crop. Acts as contact; absorbs energy produced by photosynthesis forming peroxides that disrupt living cells.
Caution  A restricted-use pesticide. Do not ingest or inhale spray mist. Wear protective face shields, respirators, and clothing.
Site of action  Group 22: photosystem I electron diversion
Chemical family  Bipyridilium
•  asulam (Asulox)
Rate  3.34 lb ai/A
Time  Apply postemergence treatment only when weeds are between the stages of early seedling and early seed head formation.
Remarks  Use at least 20 gal water. Do not use a surfactant. Inhibits cell division or mitosis.
Caution  Do not reapply within 12 mo. Labeled for a limited number of ornamental species; consult label before use.
Site of action  Group 18: inhibits DHP synthase step
Chemical family  Carbamate
• clopyralid (Lontrel Turf and Ornamental)
Rate  Consult labels
Time  Apply when weeds are small and actively growing. For Canada thistle, apply to rosette stage but before bud stage.
Remarks  Apply over the top of labeled crops or as spot treatment to well established plantings.
Caution  Do not exceed 1.3 pints/A per season. Avoid drift or treatment near susceptible crops or unlabeled and desirable plants.
Site of action  Group 4: synthetic auxin
Chemical family  Pyridine
•  fluazifop (Fusilade II or Ornamec Over-the-Top)
Rate  0.25 to 0.375 lb ai/A (16 to 24 oz/A Fusilade II) 
Time  Apply to actively growing grasses or within 7 days after irrigation with 0.25% nonionic surfactant. 
Remarks  For selective postemergence grass control. Identify grasses and adjust rates for susceptibility and stage of growth as on label. Note lists of ornamentals and associated instructions regarding topical versus directed sprays. Results often are erratic if grasses are stressed from lack of vigor, drought, high temperature, or low fertility. More mature grasses and quackgrass can be controlled but may require two applications. Annual bluegrass and all fine fescues resist treatment. Do not tank-mix with other pesticides. Inhibits fatty acid production, cell membranes, and new growth.
Caution  Do not apply within 5 days of other pesticide treatments. Grazing is prohibited. 
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Aryloxyphenoxy propionate
•  fenoxaprop (Acclaim Extra) 
use only in established ornamentals
Rate  0.04 to 0.17 lb ai/A (9 to 39 fl oz/A)
Remarks  For selective postemergence grass control. Adjust rates depending on number of grass tillers (see label). Thoroughly cover actively growing, susceptible grasses. Repeat after grass begins active growth, but do not exceed 120 fl oz/A per season. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Aryloxyphenoxy propionate
•  sethoxydim (Segment or Vantage; registered only in Washington)
Rate  0.28 to 0.47 lb ai/A (36 to 60 fl oz/A)
Time  Apply at optimum growth stage listed on label.
Remarks  For selective postemergence grass control. Identify susceptible grasses. Results often are erratic on grasses stunted or stressed from drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues; quackgrass can be suppressed. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  clethodim (Prism, registered only in Oregon; or Envoy)
Rate  0.095 to 0.25 lb ai/A (13 to 34 oz/A Envoy)
Time  Apply postemergence to actively growing annual or perennial grasses as listed on label.
Remarks  For selective postemergence grass control. Consider environmental and plant growth conditions that affect leaf uptake; see label.
Caution  Do not exceed 68 fl oz/A per season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione

Greenhouse Floors
Ed Peachey
Revised November 28, 2008

Diligent sanitation is the key to successful weed control inside greenhouses. Weed control also requires special precautions and using herbicides that have little or no chance to vaporize. Consequently, no preemergence herbicides are registered for use inside greenhouses. Always turn off ventilation fans while applying postemergence herbicides, and avoid contact with desirable vegetation. 
GREENHOUSE FLOORS—Nonresidual Weed Control
•  diquat (Reward)
Rate  0.5 to 1 quart/100 gal water
Time  Apply with nonionic surfactant any time weeds are small and actively growing.
Remarks  Avoid spray contact with desirable ornamental plants. Acts as contact; absorbs energy produced by photosynthesis forming peroxides that disrupt living cells.
Caution  A moderately toxic herbicide that requires protective face shields, respirators, and clothing for handling and application.  Do not ingest or inhale spray mist.
Site of action  Group 22: photosystem I electron diversion
Chemical family  Bipyridilium 
•  glyphosate (numerous products)
Rate  Consult labels
Time  Apply to actively growing weeds when desired vegetation is out of greenhouse and air circulation fans are turned off.
Remarks  Consult label for specific rates, application times, and species controlled. Honcho requires adding a nonionic surfactant; Expedite Application Equipment contains a specific formulation using small-droplet technology.
Caution  Do not exceed 10.6 lb ai/A per year. 
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted.
•  clethodim (Envoy)
Rate  0.095 to 0.25 lb ai/A (13 to 34 oz Envoy/A)
Time  Apply postemergence to actively growing annual or perennial grasses as listed on label.
Remarks  Consider environmental and plant growth conditions that affect leaf uptake (see label).
Caution  Do not exceed 68 fl oz/A per season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  pelargonic acid (Scythe)
Rate  Broadcast—3 to 10 gal product/100 gal water; spot spray—1 to 10% solution (1 to 13 fl oz/gal) to cover 400 sq ft
Time  Apply to thoroughly wet weed foliage in and around greenhouse, under benches, or preemergence in seedling beds. 
Remarks  Avoid contact with desirable plants. Disrupts cell membranes, causing leakage and symptoms of leaf burn. 
Site of action  Group 26: unknown
Chemical family  Carboxylic acid

Conifer Seedbeds 
Ed Peachey
Revised November 28, 2008

Conifer seedlings are extremely poor competitors during the first 2 yr in a seedbed. Consequently, selecting a site that contains few weeds, or weeds that can be controlled with current technologies, is imperative. Complete elimination of all perennial weeds and proper seedbed preparation is essential. Constant surveillance coupled with regular and timely weed control practices is required to maintain weed-free seedbeds and nurseries. Consult labels for tolerant crops.
CONIFER SEEDBEDS—Preemergence Control before Conifers Germinate
•  glyphosate (numerous product names)
Rate  Consult labels
Time  Apply to emerged weeds just before conifer seedlings emerge using similar techniques described on the label under “cropping systems” for various cereal and vegetable crops.
Remarks  Also, consult the Vegetable Crops section of this handbook for information about the stale seedbed technique. Use lower rates on vigorous annual weeds. Inhibits production of three amino acids and protein synthesis.
Caution  Do not exceed 10.6 lb ai/A (10.6 quarts/A) per season. 
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
•  oxyfluorfen (Goaltender)  
Rate  0.25 to 1 lb ai/A (0.5 to 2 pints/A)
Time  Preemergence to weeds and conifers.
Remarks  Irrigate with 0.5 to 0.75 inch water or rain for preemergence control of annual grass and broadleaf weeds. Goaltender is a contact-type herbicide with some soil residual activity. 
Site of action Group  14: protoporphyrinogen oxidase inhibitor 
Chemical family  Diphenylether 
•  oxyfluorfen (Goal 2XL)
Rate  0.25 to 1 lb ai/A (1 to 4 pints/A Goal 2XL)
Time  Apply after seeding but before conifers emerge; sprinkler-irrigate with 0.5 to 0.75 inch water.
Remarks  Use 0.5-lb rate when grass weeds are present and highest rate when extreme weed infestations are expected. Acts as contact-type herbicide when weeds are emerging.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  Diphenylether
CONIFER SEEDBEDS—Established Crops, Preemergence Weed Control after Conifers Germinate
•  napropamide (Devrinol 50DF) 
fir and hemlock
Rate  4 to 6 ai/A (8 to 12 lb/A Devrinol 50DF)
Time  Apply any time to weed-free surface and irrigate immediately with 1 to 2 inches water.
Remarks  Consider use of several products at low rates to achieve broad spectrum weed control. Inhibits root growth. 
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Acetamide
•  S-metolachlor (Pennant Magnum)
Rate  1.24 to 2.48 lb ai/A (1.3 to 2.6 pints/A Pennant Magnum)
Time  Apply any time to weed-free surface.
Remarks  Activate herbicide with brief irrigation. Use lower rates on porous media and reduced weed infestations. Gives about 60-day control, less under very wet conditions. Inhibits seedling roots and/or shoots.
Caution  Do not exceed 4 lb ai/A per year in a given area. To minimize potential for crop injury, consider using several products at low rates to achieve broad-spectrum weed control
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  dimethenamid-P (Outlook)
Rate  0.98 lb ai/A (21 fl oz)
Time  Apply 3 days after transplanting conifers and prior to weed emergence.
Remarks  Conifer species including Douglas-fir, western red cedar and western hemlock. Special local needs labels OR‑060006 and WA‑060014. Activate herbicide with brief irrigation. Inhibits seedling roots and/or shoots.
Caution  Do not apply to seedbeds.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  oxyfluorfen (Goaltender)  
Rate  0.25 to 0.5 lb ai/A (0.5 to 1 pints/A) for 5-wk-old seedlings; 1 to 2 lb ai/A (2 to 4 pints/A) for 2-0 conifers.
Time  Apply at least 5 wk after emergence. Apply to 2-0 conifers in winter dormancy fall through winter. After transplanting, irrigate with 0.5 to 0.75 inch water or rain for preemergence control of annual grass and broadleaf weeds. Do not exceed 2 lb ai/A in 1 yr. 
Remarks  Postemergence applications control susceptible broadleaf weeds up to 4 inches tall. Goaltender is a contact-type herbicide with some soil residual activity. 
Site of action Group 14: protoporphyrinogen oxidase inhibitor 
Chemical family Diphenylether 
•  oxadiazon (Ronstar 2G)
Rate  Consult label
Time  Apply uniformly with granular applicator any time to weed-free surface. Irrigate with 0.25 to 0.33 inch water immediately after application.
Remarks  Pink family (Caryophyllaceae) weeds—chickweed, mouseear chickweed, and pearlwort—are resistant. Controls weed seedlings by contact action during emergence.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor 
Chemical family  Oxadiazole
CONIFER SEEDBEDS—Postemergence Weed Control
• napropamide (Devrinol 50DF) 
fir and hemlock
Rate  4 to 6 lb ai/A (8 to 12 lb/A Devrinol 50DF)
Time  Apply only to established or transplanted stock
Remarks  Consider using several products at low rates to broaden spectrum of weed control. Inhibits root growth.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Acetamide
•  fluazifop (Fusilade II or Ornamec Over-the-Top)
Rate  Consult label 
Time  Apply to established ornamental seedbeds as topical or directed sprays according to lists and associated instructions on the label. Apply to actively growing grasses, or within 7 days after irrigation, with 0.25% nonionic surfactant. 
Remarks  Identify grasses and adjust rates for susceptibility and stage of weed growth as on label. Results often are erratic if grasses are stressed by lack of vigor, drought, heat, or low fertility. More mature grasses and quackgrass can be controlled but may need two applications. Annual bluegrass and all fine fescues resist treatment. Inhibits fatty acid production, cell membranes, and new growth.
Caution  Do not tank-mix with other pesticides or apply within 5 days of other pesticide treatments. Grazing is prohibited. 
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Aryloxyphenoxy propionate
•  sethoxydim (Segment or Vantage, registered only in Washington)
Rate  0.28 to 0.47 lb ai/A (36 to 60 fl oz/A)
Time  Apply at optimum growth stage listed on the label. 
Remarks  Identify susceptible grasses. Control often is erratic on grasses stunted or stressed from drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues, whereas quackgrass can be suppressed. Inhibits fatty acid production, cell membranes, and new growth.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
•  clethodim (Envoy)
consult label for tree species
Rate  0.095 to 0.25 lb ai/A (13 to 34 oz/A Envoy)
Time  Apply postemergence to actively growing annual or perennial grasses listed on label. 
Remarks  Consider environmental and plant growth conditions that affect leaf uptake; see label. 
Caution  Do not exceed 68 fl oz/A per season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
CONIFER SEEDBEDS—Spot Treatments with Selective Equipment
•  glyphosate (numerous products)
Rate  Wiper—33% solution
Time  Apply with selective wiper when weeds are at least 6 inches taller than crop but after active growth stage of conifer, when buds are mature.
Remarks  Mix 1 gal product in 2 gal water. Avoid contact with desirable vegetation. Inhibits production of three amino acids and protein synthesis.
Caution  Do not broadcast over conifers in nurseries. Although not explicit on the label, this use is included under industrial uses. 
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
•  glyphosate (several products)
Rate  Consult label for rate
Remarks  Spot treatments applied with a paint brush or similar device to curly dock, Canada thistle, and horsetail have proven satisfactory if extreme care is taken to avoid contact with conifer seedlings. (See comments above.)
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
•  oxyfluorfen (Goal 2XL)
Rate  0.25 to 0.5 lb ai/A (1 to 2 pints/A Goal 2XL)
Time  Apply in at least 20 gal water at least 5 wk after emergence or bud break, or while trees are dormant and weeds are less than 4 inches tall.
Remarks  Two or three applications may be needed to control some weeds, especially if they have four or more leaves. Allow 24 hr after application for evidence of contact activity before irrigation. Acts as a contact-type herbicide.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  Diphenylether
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