Weed management in home landscapes and gardens
Ed Peachey
Reviewed December 4, 2008

Use pesticides safely!
Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use.
Read the pesticide label—even if you’ve used the pesticide before. Precisely follow label instructions (and any other directions you have).
Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from your pesticide use.

Annual and especially perennial weeds require a year-round approach combining several weed control practices into an integrated weed management program. Perennial weeds are especially difficult to control in horticultural sites. Once established, most contain large storage organs such as roots, rhizomes, tubers, or trunks and vines. Some contain thorns, one or more are poisonous, and most are extremely vigorous. All weeds, if left unmanaged, reduce the value of the land they occupy. Control options must weaken perennial weeds or prevent their establishing as perennials in horticultural sites.
Design your landscape. In home gardens, orchards, or berry patches, weed control activities can be minimized with careful selection of weeding methods that are compatible with you and the desirable plants. Grouping plants that require similar weed control practices will improve efficiencies. Combine several weed control practices into a year-round weed management program designed to prevent weed growth.
Consider the following steps in designing a year-round weed management approach for home landscapes and gardens.
Know your weeds. Accurate weed identification is essential for successful weed management in home landscapes and gardens. Learn to identify common weeds by obtaining copies of weed identification publications listed at the end of this section. Also, consult local lawn and garden stores, nurseries, or your county Extension agent and Master Gardeners at the Extension office.
Learn to identify both mature and seedling weeds. Correct identification of perennials in the seedling stage can provide control options while the plant is small and vulnerable. After weeds become established as perennials, control options are limited to brief stages within the weed life cycle. Control practices often must be repeated or combined with other methods for maximum control.
Weed control options. Year-round weed management combines good crop production practices with as many weed control options as possible. Choice of options depends on effectiveness and your preference in completing timely and often repetitious tasks.
Prevent seedling weeds from becoming established. Control of perennial seedlings within the first 4 to 6 wk after emergence when plants are small and easily removed will prevent their establishment as perennials. Prevent mature plants from producing seed or viable perennial parts such as new tubers or rhizomes.
Proper landscape or crop management shifts the competitive advantage in favor of the crop instead of the weed. Choose a site or improve the area for optimum growth of landscape plants. Buy clean topsoil and nursery plants. Control perennial weeds before planting the landscape. If this is impossible, choose vigorous ground covers or ornamental plants that compete against weeds or can be treated easily by combining weed management practices. Plant these ornamentals in closely spaced arrangements and place fertilizer or use drip irrigation to enhance crop vigor while minimizing weed growth. A vigorous turfgrass or living mulch can be managed on some sites to suppress weeds.
Plastic mulches—or, better yet, woven mats covered with bark—will control most weeds, including many perennials, except weeds like quackgrass or yellow nutsedge with sharp underground rhizomes. Woven mats block perennial weed emergence while allowing complete drainage and oxygen exchange into the soil. After installation, prevent weed establishment within the bark mulch.
In home food gardens, use drip irrigation in berries or orchards to direct fertilizer and water to crops rather than broadcast for use by weeds. Minimize the open space by interplanting short-duration vegetables between crops of longer duration. Select crops and planting dates that rapidly form a complete canopy to shade weeds. Green beans, cucumbers, and squash are good examples of broadleaf vegetables that provide competitive canopies. In berries and tree fruits, dwarf turfgrasses can be managed as a living mulch. Turfgrasses reduce weed growth by filling 50 to 66% of the space with a competitive cover while a weed-free strip is maintained within the tree or berry row.
Cultivation or hand removal requires frequent scouting and cutting or pulling. Annual weeds must be cut just below the soil surface to prevent resprouting from buds on the stem. Always maintain a sharp hoe or knife and minimize soil disturbance. Shallow cultivation is required in tree fruits and berries to avoid scarring roots. Fewer weeds will grow after the initial population near the soil surface has germinated. Remove weeds such as common purslane from the garden area, since they dry slowly and often reroot. In vegetable gardens, annual tilling will improve planting conditions while controlling most weeds and covering debris from last year. However, tillage conducted too often or when soils are excessively moist will promote soil compaction and a “hardpan” usually several inches below the soil surface.
Weed infestations are rarely eliminated using cultivation or hand removal. However, exceptions include frequent scouting to eliminate new perennial weed seedlings and starvation of established perennials. Starvation requires cutting the weed every 2 to 3 wk for 2 yr or more to completely prevent storage of food reserves. Repeated harrowing and physical removal of weeds or drying of the soil will reduce infestations of perennials that remain near the surface. Otherwise, cultivation and especially rototilling chops and rapidly spreads most perennial weeds throughout the site.
Herbicidal control involves chemicals that selectively control unwanted vegetation when applied correctly. Herbicides require considerable testing to assess potential hazards and to minimize possible crop injury before the product can be sold. Product labels describe specific uses and provide detailed instructions. Users must read and follow label instructions precisely to reduce human exposure and prevent crop injury.
Herbicides often are specially formulated and sold in small packages for use by home landscapers. Always verify that the crop you intend to treat is listed on the package. If not, avoid application to that crop to reduce possible crop injury and residues in your food. Apply the herbicide to the crop or site exactly as listed on the package. Be especially careful about drift or misapplication to desirable plants. Avoid applications during windy conditions or spraying too close to desirable vegetation not listed on the label.
Apply herbicides at exactly the correct rate or concentration and time of year. Use one of the methods below depending on label instructions and the weed to be controlled.
1. Sprays must be applied precisely to a measured area or mixed at a specific concentration and applied to wet the weed foliage. Hose-end sprayers are poor choices of application equipment. Rather, use a pressurized hand-held or backpack sprayer and reserve it for herbicides only. Either calibrate your sprayer by spraying the amount of water on the prescribed area stated on the label (e.g., 1 gal/250 sq ft), or spray the area to be treated with water and measure the amount used. Mix the correct amount of liquid herbicide in water and treat the exact area. While spraying, do not stop to concentrate spray on a specific weed. Apply the spray uniformly over the entire area.
2. Spot or foliar spraying directs a narrow stream of spray toward the weed. Herbicides often are diluted to a certain concentration (e.g., 3 Tbsp/quart of water). Spray weed foliage until it is uniformly wet but not dripping.
3. Basal spray completely wets the lower 18 inches of all stems or trunks until spray runs down and collects around the collar and exposed roots. Stump spray thoroughly drenches newly cut surfaces including bark and exposed roots.
4. Concentrate treatments apply undiluted herbicide on newly cut stumps or in frills cut with an ax on larger stumps. Frills must be cut through the bark and undiluted chemical poured into the opening. Drill holes also can be bored in the wood near the outside of the trunk, filled with undiluted chemical, and plugged with a dowel.
5. Granular herbicides, including “weed and feed” products, also must be applied precisely to known areas. Measure small areas and apply exact quantities of chemical to that area. Avoid using the visual guides printed on product labels because they lack precision.
Pesticide safety requires common sense. Always keep a pesticide in its original container with the label clearly visible. Do not put chemicals in empty food or drink containers. Store herbicides and your sprayer in a locked cabinet, out of the reach of children, away from foods, and in a ventilated area protected from freezing. Rinse the sprayer thoroughly after each use. Let metal sprayers dry to prevent rusting.
Herbicide selection requires information about each weed and herbicide including the precise time of application. First, identify the weed accurately before studying control options. 
Next, determine the susceptible growth stage or best time of year to achieve maximum control. Last, consider the unique properties and application requirements for each herbicide.
For example, herbicides can be applied selectively to soil or selectively to foliage; or, they can be applied nonselectively to foliage or nonselectively to soil.
1. Apply herbicide selectively to soil (preemergence) to kill germinating weed seedlings among established plants. Preemergence herbicides remain near the soil surface where weed roots and shoots absorb the chemical and die. Established perennials survive because their roots grow beneath the treated layer.
If you want to use this kind of herbicide in annual flower and bulb beds and among certain vegetables, ask for products that contain trifluralin or oryzalin. Verify that your crop or site is listed on the label.
If you want to use this kind of herbicide around established shrubs, trees, berries, tree fruits, and conifers, ask for products containing trifluralin, oryzalin, or dichlobenil  (do not apply around conifers or over ground covers). Apply dichlobenil only in midwinter when temperatures are above freezing but below 50°F and when a rain will follow your application. Dichlobenil volatilizes (evaporates) into the atmosphere when temperatures are too warm.
Corn gluten meal inhibits root development and kills seedlings under moisture stress. Research and home garden results show poor or no control of weed seedlings in the Pacific Northwest, especially in wet spring weather. Recent Pacific Northwest trials showed dramatic increase in weed seedling root growth when corn gluten meal was added to control weeds.
2.  Applying herbicides selectively to foliage (postemergence) kills undesirable foliage, such as broadleaf weeds growing in turf. Selective foliar herbicides are absorbed mostly by leaves and move through the weed’s vascular system to growth sites; there, the chemical disrupts growth and thus leads to death. To use this type of herbicide safely, you must know both the weed’s susceptibility and the desired plant’s tolerance to the chemical. Apply these herbicides carefully to prevent their accidentally drifting or volatilizing onto nearby susceptible, desirable plants.
In lawns, herbicides containing 2,4-D, MCPP, MCPA, and dicamba will control most broadleaf weeds. However, if these chemicals drift they can injure or kill adjacent plants. Select products with very small amounts of dicamba, or be extremely careful in applying dicamba because it can injure or kill susceptible trees or shrubs growing in or near the treated lawn. The desired plants’ roots under the lawn can absorb dicamba, resulting in injury.
In landscapes, the postemergence grass herbicides containing fluazifop or sethoxydim will control certain annual grasses and suppress or control some perennial grasses growing among broadleaf plants. All fine fescues and annual bluegrass are tolerant. Often, a surfactant is needed to enhance the weed’s uptake of the herbicide.
3. Applying herbicide nonselectively to foliage (either a contact-type herbicide or a systemic-type herbicide) kills most treated plants. The treatment can still be selective, however, if you use certain timing—destroying emerged weeds before you plant the desired plants—or if you carefully direct the chemical on the weed, avoiding contact with desirable foliage. This type of herbicide does not leave long-lasting residues in soil.
Contact herbicides such as glufosinate (Finale), diquat, herbicidal soaps (Safer), and pelargonic acid or cacodylic acid products disrupt cell membranes, causing leakage and rapid desiccation of foliage. Small, rapidly growing broadleaf weeds and annual grasses with exposed growing points are most sensitive. Most perennial weeds regrow soon after treatment because foliage is controlled but roots survive. Some products include acifluorfen or oxyfluorfen to broaden the spectrum of weed control or to hasten foliage death.
Acetic and/or citric acids  cause cell contents to leak, resulting in burned leaves of small, actively growing broadleaf and grass weeds. However, if growing points of grasses are protected beneath the soil surface, control will be erratic, and nonexistent for perennial weeds with ample reserves of starches and nutrients. Perennial weed leaves will be burned with these products. However, buds from rhizomes or roots below the treated area will require multiple treatments. Research has shown that some perennial weeds can be controlled with repeated tillage every 3 wk for 3 yr. Claims of “changing soil pH with drenches” or that the drench has “no effect on soilborne organisms” need to be considered with common sense. Soils are buffered against fast changes of pH, and most soil organisms respond quickly to environmental conditions. These are weak acids requiring careful handling during application. They can irritate the skin or harm eyes and throat. In Oregon and Washington, registrations and labels differ due to differing interpretations of laws and how companies are registering the products. Users and purchasers need to be informed and to know that they are responsible for their decisions.
Systemic herbicides enter leaves and move to sites in the plant that control growth. This type of herbicide can control many perennial weeds, although application timing is critical.
•  Glyphosate (several products) controls a wide range of grasses and broadleaf plants by inhibiting production of three essential amino acids or protein building blocks in plants. The herbicide moves more efficiently from leaves to perennial roots if it is applied to actively growing foliage, usually in midseason before bloom; consult label for details on specific weeds. In soil, glyphosate is chelated, that is, rendered ineffective. Repeated glyphosate treatment of weeds in Australian orchards over several years has resulted in weed biotypes that resist the treatment. To minimize the chances for weeds to develop resistance, rotate and combine weed control practices. Avoiding dominance and infestations by a single weed over many years also contributes to biodiversity and control. 
•  Triclopyr and 2,4-D products applied to foliage and cut stems will control many broadleaf and woody plants. Choose amine formulations to reduce the chance that the herbicide will volatilize and move to neighbors’ property or to desired plants on your property. Crossbow is a combination of triclopyr and 2,4-D in an ester formulation. It must be applied when temperatures will be below 60°F for a couple of days to prevent volatility.
4.  Applying nonselective persistent herbicides to soil (soil residuals and sterilants) controls all vegetation for an extended time in, for example, on driveways, along foundations, or under fencelines. Desirable plants can be severely injured if their roots grow into the treated area or if treated soil is moved. This type of herbicide product contains prometon, monobor chlorate, sodium chlorate, or sodium metaborate.
Roof moss can be controlled with elemental zinc or with Tide laundry detergent. 
Year-round Weed Management
Designing a year-round weed management program requires planning and timely implementation. First, identify and prioritize the weeds infesting your home landscape or garden. You may decide to simply mow a weed that infests sod between buildings, while poison-oak or field bindweed may be intolerable near the front door or in your garden! Also, improve your weed and crop management efficiency by grouping plants that require similar practices.
Second, combine several control methods with management practices to improve crop competitiveness. Interplant crops and space plants closely to shade and compete against weeds. In food production areas, isolate perennial weed infestations and plan an attack while crops are absent. Always keep seedlings or new plants from becoming established plants, especially as perennial weeds. Apply controls at the correct time. If you choose to apply herbicides, read the information and the product label. Then calibrate your equipment and apply precisely the amount stated on the package.
Last, evaluate and continually monitor the infestation. Modify your choice of controls if results are not satisfactory. Remember, weed control requires patience and persistence!
Information about creeping woodsorrel, mistletoe, nutsedge, poison-oak, wild blackberry, and weed management in landscapes is available from University of California http://www.ipm.ucdavis.edu/PMG/selectnewpest.home.html
Weed Treatments and Times of Application for Home Landscapes

Weed	
Cultivation1
(soil drying)	
Geo-textiles2	Herbicides	
			2,4-D	
triclopyr	
glyphosate	
dichlobenil	
Annual weeds	any time	All	not labeled	not labeled	spot treat	midwinter	
Quackgrass	dry season3	laminate	not effective	not effective	May—active	midwinter growth	
Field bindweed
  (morning glory)	not effective	All	treat 2–3 times/yr3	midbloom3	midbloom3	midwinter	
Blackberry (all)	not effective	All	growing season	active growth	September	not effective	
Canada thistle	not effective	All	prebloom	prebloom	bloom	midwinter	
Dandelion
(common and false)	any time	All	growing season	growing season
(active growth)	any time	midwinter	
Poison-oak	any time	All	growing season	active growth before leaves turn red	midsummer	not effective	
Horsetail rush Equisetum	dry season	All	not effective	not effective	not effective	midwinter	
Yellow nutsedge	dry season	laminate	not effective	not effective	by mid-June4	midwinter	
Curly dock	any time	all	growing season	growing season	prebloom	midwinter	
1 Cultivation and complete hand removal every 2 to 3 wk will starve perennial weeds and eventually cause death in 2 yr or more.
2 Geo-textiles include spunbonded, woven, and laminated plastic fibers that can be applied anytime. Pointed rhizomes and roots of emerging weeds can penetrate the fabrics (except the laminate).
3 Infestation suppressed.
4 Infestation suppressed slightly.

Weed Control Options 
for Home Gardens and Orchards
Weed Management Option	Vegetables*	Berries*	Tree Fruits*	
Cultivation or plowing	yes	no	no	
Plastic mulch	no	no	sometimes	
Interplanting	yes	turfgrass	turfgrass	
Glyphosate (several products)	preplant	grapes only	apples and pears	
*See labels for specific vegetables, berries, and tree fruits.
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