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How to Manage PestsUC Pest Management Guidelines
A dense, vigorously growing, competitive stand of turfgrass will resist invasion by weeds. Integrated weed management focuses on selecting, establishing, and maintaining a competitive stand of turf. While it is difficult to eliminate all weeds from turf, in highly maintained turf it is possible to prevent large irregular patches of weeds, which make turf unattractive and reduce its utility. The objective of an integrated weed management program is to keep weed populations below levels that are incompatible with the purpose of the turf. The first step is preparing the site properly and choosing an appropriate turfgrass species for the location, followed by cultural practices that contribute to turf vigor, such as proper irrigation, mowing, fertilization, thatch removal, and aeration. The increased vigor allows turf to better withstand insect, disease, and nematode damage and to recover more quickly. Healthy turf can also out-compete weeds and reduce the chances of their becoming established. Herbicides are used as tools in turf management where high quality turf is required; however, their use should be integrated with a good cultural program. SELECTING A TURFGRASSTurf species and cultivars vary in their adaptability to different areas of California. Choosing a well-adapted cultivar to plant will be one of your most important weed management decisions (see section on TURFGRASS SPECIES). Cool-season species (bentgrass, bluegrass, perennial ryegrass, and tall fescue) are most competitive in the coastal and northern regions of California; some of the newer cultivars of perennial ryegrass, Kentucky bluegrass and tall fescue are more competitive and grow better than the old cultivars. Warm-season species (bermudagrass, St. Augustinegrass, zoysiagrass, and dichondra) are most competitive with weeds in the interior valleys and desert regions. When turf species are planted in areas where they are not well adapted, they require greater care (e.g. management skills and resources) to grow and maintain and are more susceptible to invasion by weeds. Irrigation, mowing, and fertilization requirements vary for each turf species and must be carefully followed to maintain their competitive edge against weed invasions. TURF ESTABLISHMENT (Before planting turf or when renovating weedy turf)Before planting, annual weeds can be controlled by irrigating to germinate weed seeds in soil, followed by shallow cultivation or application of a contact herbicide. Repeat this process two or three times to improve the chances of establishing a turfgrass with a minimum of weeds. Using turfgrass sod in well prepared soil that has been cultivated and amended to improve water-holding capacity in sandy soil or to improve drainage in clay soils will decrease annual weeds. Poor drainage favors some weeds such as red sorrel, curly dock, nutsedge, annual bluegrass, and crabgrass. Populations of some perennial weeds such as dallisgrass, bermudagrass, and purple nutsedge can be reduced before planting turf by cultivating in summer and keeping the soil completely dry to dehydrate the propagules (stems, rhizomes, tubers). Rework the soil to bring up new propagules, but be sure to keep the soil dry; three to four cultivations a week or more apart may be needed for best results. MANAGING ESTABLISHED TURFTurfgrass can be established and maintained to discourage weeds in the turf or to decrease chances for weed invasion. Any condition that exposes the soil surface to additional light makes that area more susceptible to weed invasion. Factors that contribute to poor turf quality and vigor include overwatering or underwatering, mowing too low or too high, low fertility, excessive wear, disease or insect damage, soil compaction, and excessive shading. Irrigation Management. California has a Mediterranean climate that is characterized by rainfall in winter and spring and very little rainfall in summer and fall. Irrigation is needed, therefore, for both cool and warm-season turfgrasses. It is very important to follow good irrigation practices, regardless of turfgrass species used, so that optimum growth and development of turfgrass is obtained. Most turfgrass sites in California are irrigated with a sprinkler irrigation system. A uniform application of water is extremely important for maximum efficiency because it is important to avoid wet and dry spots within the sward. Turf is weakened in wet spots because of poor soil aeration and root disease that can result in the invasion of shallow-rooted weeds such as crabgrass, annual bluegrass, and oxalis. Runoff from overirrigated areas is wasteful and results in accumulation of water in low parts of the sward. In contrast, dry sites will be characterized by turf of poor color, density, and uniformity that allows the invasion of deep-rooted weeds such as bermudagrass, dandelions, plantains, clover, knotweed, and yarrow. Proper timing and an adequate amount of irrigation are necessary for optimum growth, maximum quality, and best appearance of the respective turfgrass species. Warm-season turfgrass species require less irrigation than cool-season turfgrass species. Common warm-season turfgrass species in California include common and hybrid bermudagrass, St. Augustinegrass, kikuyugrass, and zoysiagrass. The most commonly planted cool-season turfgrasses for California are tall fescue, Kentucky bluegrass, and perennial ryegrass, which are the higher water-use-rate-grasses. Water use rates vary based on location (low desert valleys can approach 0.37 inches per day in July, while during the same period turfgrass in northern coastal regions may require only 0.12 inches per day). The table below shows the relative water use rates of turfgrass types for three different locations in California. See local newspapers or contact local Cooperative Extension offices for the water required in specific areas.
Key points for maximum irrigation efficiency:
Fertilization. Proper fertilization of turfgrass is an important component in producing vigorous, dense growth. Low fertility, especially low nitrogen, is one of the factors that allows weeds to invade turf. For example, clovers tend to grow well in areas of low soil nitrogen because they can fix nitrogen in their roots. Therefore, where clovers are a problem, increase nitrogen fertilization to make the turfgrass more competitive. Apply nitrogen about four times during the year when the turf is actively growing (see Table 2). For slow-release fertilizers, make applications at 6- to 8-week intervals; for other fertilizers, applications are made at 4- to 6-week intervals. Use the following guidelines to determine application rates for the different turfgrass species:
Mowing. Correct mowing height and frequency of mowing is critical for preventing weed invasion. Different turfgrass species have different mowing height requirements. Mowing Kentucky bluegrass too short (shorter than 1.5 inches) weakens the turf and encourages weed growth. Conversely, mowing bermudagrass too long (longer than 1 to 2 inches) results in a buildup of thatch, which reduces the competitive ability of the grass. The table below outlines the correct mowing height for the different turfgrass species.
Mow turfgrass so that no more than one-third of the leaf blade is taken off at each cutting. In the summer months, cool-season turfgrasses (Kentucky bluegrass, perennial ryegrass, fine fescue, tall fescue and colonial bentgrass) may be mowed at the higher height. Weedy turfgrass areas need to be mowed frequently so that they don't develop a patchy appearance caused by uneven growth of the weeds. Common weeds that require frequent mowing to prevent patchiness and seedhead development are annual bluegrass and annual ryegrass in winter and crabgrass, dallisgrass, and yellow nutsedge in summer. Thatch Removal and Aeration. Thatch develops in turfgrass when dead leaves, rhizomes, stolons, and stems accumulate faster than they are decomposed. Creeping species such as bentgrass, bermudagrass, zoysiagrass, St. Augustinegrass, and kikuyugrass can produce a thick thatch. Removing thatch increases the turfgrass vigor, reduces scalping by the mower, and gives a more uniform appearance to the turfgrass. Thatch can reduce the effectiveness of preemergence herbicides by either (1) binding with the herbicides and making them ineffective or (2) increasing degradation of the herbicides as a result of the increased activity of microorganisms living in the thatch. Thatch removal (by verticutting) should be done before preemergence herbicides are applied; otherwise the herbicide will be removed or its activity will be decreased. The same principle applies to aeration. Apply herbicides after aeration to get maximum control of the weeds. MONITORINGRegular weed surveys (winter, spring, and summer) will help determine what species are present, their approximate population levels, and what types of management practices may be necessary. Use Turfgrass Pests, UC ANR Publication 4053; Grower's Weed Identification Handbook, UC ANR Publication 4030; Weeds of the West, UC ANR Publication 3350; the UC IPM online weed photo gallery or the UC IPM online Guide to Healthy Lawns. Use a form such as the following one to keep written records of monitoring results. (This form can also be adapted to use in a spreadsheet computer program.) A written weed history will aid in making future weed management decisions.
HERBICIDESHerbicides are an effective tool where high quality turf is desired. However, they must be applied with care and accuracy and in the context of a good overall turf management program. Before using any herbicide, carefully review the label for conditions of use including rates, methods of application, and precautions. Never use an herbicide in any manner contrary to its label and be sure that the herbicide will not injure the turfgrass species (see table on Sensitivity of Turf Species to Herbicides). When using any herbicide for the first time, apply it at the recommended rate on a limited area to make sure it is successful under local conditions. Excessive rates, improper timing, or application errors of selective herbicides can injure or kill desirable turf. Insufficient application, on the other hand, usually results in failure or incomplete weed control. Be aware of formulation changes for the herbicide; new formulations may result in turf injury even though no injury was noted in previous formulations. In some cases adjuvants are used with herbicides. Adjuvants are compounds that modify a spray solution. These include wetting agents, surfactants, spreaders, emulsifiers, and solvents. Adjuvants can enhance herbicide activity and/or reduce herbicide selectivity. Some adjuvants alone can cause injury to turf. Adjuvants should only be used when called for by the product label. Herbicides can be broadcast or used for spot treating areas. The extent of the weed infestation will determine which application method to use. Broadcast applications can be made either by spraying herbicides mixed in water or by applying herbicides fixed to granules. Small scattered weed infestations should be controlled with spot applications. Larger more uniform weed infestations should be controlled with broadcast applications. To increase the uniformity of granular applications apply one-half of the required herbicide over the entire area to be treated in one direction (north-to-south) and the other half over the entire area in the perpendicular direction (east-to-west). Before making broadcast spray applications, carefully calibrate the sprayer to insure accuracy. See The Safe and Effective Use of Pesticides, UC ANR Publication 3324 for additional information. Spot treatment with selective herbicides such as 2,4-D is useful in small areas. Be sure to apply the recommended rate and concentration. Be careful not to prolong application over individual spots as over-application can occur and result in turf injury to the surrounding area. Spot treatments are also useful with nonselective herbicides such as glyphosate when used to control individual clumps of weeds such as tall fescue, dallisgrass, or nutsedge. When applying the herbicide, apply just enough spray to wet the leaves of the weed. Do not allow the application equipment to drip or leak between spot applications. Also, do not walk through the treated area onto untreated turf. Severe turf injury can result from the herbicide dripping onto the turfgrass or by being moved on the soles of shoes. If the weed is taller than the turf, the herbicide can be applied with a sponge or wick wiper, giving a selective application to the weed. SITE PREPARATION. Four herbicides that can be used for preplant use on areas to be planted with turfgrass are glyphosate (Roundup Pro), dazomet (Basamid), metham (Vapam) and methyl bromide. Glyphosate is a translocated herbicide used primarily for control of perennial weeds. Methyl bromide is a nonselective soil fumigant that requires special application techniques using a vaporproof covering like polyethylene. A polyethylene covering will also increase the control of the soil fumigants dazomet and metham. Preplant fumigation of a site can kill bermudagrass, nutsedge, and other perennials, as well as all existing annual plants and many germinating seeds. Newly Established Turf. Bromoxynil (Buctril) can be applied to newly emerged turf when it is about one month old to control seedling broadleaf weeds. Siduron (Tupersan) can be used on newly seeded or established, cool-season turfgrass for control of broadleaf seedlings and warm-season grasses. DCPA (Dacthal) can be used "at greening" when a solid stand of turf is apparent. Postemergent herbicides such as 2,4-D, dicamba, or triclopyr can be used for broadleaf control once the turf has produced several tillers and has been mowed two or three times. Established Turf. Herbicides may be applied before (preemergent) or after (postemergent) weeds emerge. Preemergent herbicides used to control weeds in turf are applied to the soil before the weed seeds germinate; most are moved into the top 1 to 3 inches of soil by rain or irrigation where they will be taken up by the roots and shoots of the emerging weeds. Preemergent herbicides include atrazine (Drexel Atrazine), benefin (Balan), bensulide (Pre-san), DCPA (Dacthal), dithiopyr (Dimension), isoxaben (Gallery), napropamide (Devrinol), oxadiazon (Ronstar), prodiamine (Barricade), pronamide (Kerb), pendimethalin (Pre-M, Pendulum), and the combination materials benefin plus trifluralin (Team), and benefin plus oryzalin (XL). Atrazine, which is labeled for sod production only, is used exclusively in St. Augustinegrass or zoysiagrass for control of annual broadleaf weeds and some annual grasses. Benefin is used primarily for annual grass control, but it will control some annual broadleaf species. Apply it 2 to 3 weeks before initial weed germination and use sprinkler irrigation to wash it off the turf leaves. Bensulide is also used primarily for control of annual grasses. Apply it before initial weed seed germination; the timing of the application depends on location in the state and the weed species targeted. Bensulide gives 4 to 6 months control of annual grasses and will inhibit germination of overseeded grass. DCPA is one of the safest herbicides for most turf species. It is used principally for crabgrass control, but will also give short term control of prostrate spurge. Dithiopyr is used on established turf for control of annual grass and some seedling broadleaf weeds. Some bentgrass cultivars and fine leaf fescue are sensitive to this material if treated during periods of severe stress. Used primarily as a preemergent herbicide to control germinating crabgrass, annual bluegrass, spurge, and oxalis, it will also control crabgrass seedlings up to the 3-leaf stage. Isoxaben is used on established turf for the control of many broadleaf weeds. Apply it in late summer to early fall for winter annuals or in early spring for summer annuals or perennial weed seedlings. For best results, follow with a sprinkler irrigation of at least 0.5 inch of water. Napropamide effectively controls crabgrass and many other annual weeds before emergence. It is currently registered on dichondra, warm-season turf and tall fescue. Oryzalin controls annual grasses and some broadleaved weeds in warm-season turf. Because it has long residual activity; a summer application may prohibit germination of a fall overseeding of winter annual grass. Oxadiazon is used in established turf principally for crabgrass control, although annual bluegrass and many annual broadleaf weeds can also be controlled. It should not be used on turfgrass greens or tees, nor is it registered for use on home lawns. Pendimethalin is used on established turf to control many weeds including crabgrass, foxtail, oxalis, and spurge. Due to its long residual period, the turf should not be overseeded with grasses for 8 to 12 weeks after application. Prodiamine is used on established turfgrass to control annual grasses and some broadleaf weeds. It is very insoluble in water and lasts for a long time, giving good control. It will interfere with overseeding of grasses for 4 to 10 months, depending on the rate used. Turfgrass must be well established before prodiamine is used or roots will be inhibited. Pronamide is used for preemergence or early postemergent control of annual bluegrass in bermudagrass turf. It is most effective in late fall at, or just before emergence. For postemergent control it takes 14 to 21 days before results are evident. Do not overseed with annual ryegrass within 90 days of treating with pronamide. Siduron is a preemergence herbicide that can be applied on newly planted, cool-season turfgrass (fescue, bluegrass or rygrass) to control seedlings of warm-season weeds, particularly crabgrass, bermudagrass, or kikuyugrass. Its primary use is in turf renovation where bermudagrass or kikuyugrass is killed with glyphosate and a cool-season grass is planted. Postemergent herbicides used in turfgrass weed control either translocate systemically or act as contact herbicides. Herbicides that translocate penetrate the leaves and stems, move in the vascular system, and eventually reach a site of action where they interfere with plant processes, ultimately killing the weeds. Herbicides that translocate include 2,4-D, MCPA, fluazifop (Fusilade), glyphosate (Roundup Pro), mecoprop (MCPP), and MSMA. Some translocated herbicides such as dicamba (Banvel) and triclopyr (Turflon) also have some soil activity and can be taken up by roots. Contact herbicides like bromoxynil (Buctril) and bentazon (Basagran) kill only the plant tissues touched by the spray, although bentazon does have some soil activity. Movement within the plant beyond the point of contact is limited. Both types of postemergent herbicides must pass through the leaves or shoots of the plant. Some herbicides are rainfast in as little as 2 hours while others should not be irrigated or rained on for at least 48 hours after application. A surfactant (adjuvant) is often added to foliar sprays to help penetrate leaves. Bentazon helps to control yellow nutsedge and selected broadleaved weeds in turf. Repeated applications are necessary for best results. Bromoxynil is a contact material used for the control of many young broadleaf weeds. It is the least phytotoxic of the postemergent materials to newly-seeded grass turf, yet controls broadleaf weeds when they are small seedlings. Clopyralid is a broadleaf herbicide that controls weeds in the legume (clover) and aster (dandelion) families. It is combined and packaged with triclopyr for control of additional broadleaved weeds. Clopyralid is for use on commercial turfgrass where clippings will not be used in off-site composting. Dicamba is a foliar-applied, translocated material that also has soil activity. Spray dicamba on calm days to avoid drift onto susceptible plants. Do not apply high rates or make repeated applications over the root zones of susceptible shrubs and trees. Dithiopyr may be used for the control of young crabgrass (large or smooth) up to the 3-leaf stage. May be combined with MSMA. See label for turfgrass species on which this material can be safely used. Ethofumesate is a translocated, selective herbicide that controls several annual grass and broadleaf weeds. It is particularly effective in an annual bluegrass management program. It has both preemergent and early (two-leaf stage) postemergent activity and is most effective in programs that use both timings. Fluazifop is a translocated, selective herbicide that controls most annual and perennial grasses. Its effectiveness is reduced when grasses are under moisture stress. Annual grasses are easiest to control when young. Higher rates of application and repeat treatments are necessary for control of perennial grasses. Glyphosate is a translocated, nonselective herbicide used for control of a broad spectrum of weeds. Apply it to rapidly growing young annual or perennial weeds at the flowering stage. Halosulfuron is used for the control of yellow and purple nutsedge and the suppression of green kyllinga. It will require more than one application for control and needs a nonionic surfactant in the spray solution. Mecoprop is a translocated, broadleaf herbicide. Because of its selectivity, it is generally safer to use on turfgrass than 2,4-D or triclopyr. Mecoprop is the safest postemergent herbicide to use on bentgrass. Mecoprop is frequently formulated into broadleaf mixes. Like 2,4-D, mecoprop has little soil activity. MCPA is a translocated, broadleaf herbicide. When used at the same rate as 2,4-D, it is less effective in the control of most weed species but somewhat safer for the turfgrass. It is often mixed with mecoprop and dicamba to increase its effectiveness. MSMA is a selective, translocated herbicide. It is used principally for crabgrass, dallisgrass, nutsedge, and green kyllinga. The degree of MSMA selectivity on turf is determined by temperature and rate, Do not use MSMA on St. Augustinegrass, bentgrasses, or kikuyugrass. Pronamide is a selective herbicide that is used to control annual bluegrass in bermudagrass turf. It controls annual bluegrass slowly by inhibiting root development and thus reducing the weed vigor. Best control is accomplished when the annual bluegrass is young and before seed head stage. Do not treat where the material can move into sensitive cool-season grass species, do not apply to a bermudagrass turfgrass that has been overseeded with a cool-season grass, and do not overseed with cool-season species for 90 days following treatment. Quinclorac is a selective, translocated herbicide that is used to control clovers and crabgrass (although some biotypes of smooth crabgrass may be resistant) and to limit the growth of kikuyugrass in warm-season turfgrass. The herbicide 2,4-D is a selective material used for broadleaf weed control. It is applied in spring when weeds are rapidly growing. Repeat treatments may be required for late emerging weeds or on perennials. This herbicide is available as an amine or ester formulation. The 2,4-D ester form is used for hard-to-kill perennial broadleaf weeds. Do not use it on newly-seeded turf, St. Augustinegrass, bentgrasses or dichondra. The amine form is generally more selective on turfgrass and is less subject to drift problems to nontarget species. Triclopyr is a translocated herbicide used for some broadleaf weeds; it is especially effective on oxalis. Do not use triclopyr on bentgrass or warm-season turf species such as common and hybrid bermudagrasses and kikuyugrass. It has some soil activity, so do not apply high rates or make repeated applications over the root zones of susceptible shrubs and trees.
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