How to Manage Pests
Pests in Gardens and Landscapes
Insects are not a common cause of residential lawn damage in California, but certain species occasionally damage or kill turfgrass. Insect feeding can cause grass to turn yellow or brown, or die, especially if the grass is already stressed. Damage usually begins in small, scattered patches, which may merge into large dead areas. However, lack of proper cultural care and use of inappropriate grass species in a particular location are more likely responsible for unhealthy or dying lawns than insects. Disease-causing pathogens, excessive or inappropriate use of chemicals such as fertilizers and herbicides, and dog urine also produce damage resembling that of insects. Before taking any insect control action, be sure that it is insects causing the problem and not something else.
Insects that may cause damage in California lawns include various root-, crown-, and leaf-feeding caterpillars; white grubs, which are the larvae of scarab beetles such as the black turfgrass ataenius and masked chafers; billbugs, which are weevils with white, grublike larvae; and chinch bugs, which are true bugs in the order Hemiptera. Each species produces somewhat different damage symptoms and must be managed differently. Study identifying characteristics and Table 1 for damage symptoms associated with each species. In addition to the pests in Table 1, leafhoppers may occur in lawns, sometimes causing yellowing of leaf blades, but rarely occur in numbers justifying treatment. Many other insects may be observed while examining grass. However, control is rarely or never needed for most types of insects because they are harmless or beneficial. Common beneficial insects include predatory ants, ground beetles, rove beetles, and blister beetles. Other common arthropods that are primarily decomposers and do no significant injury to turfgrass include springtails and millipedes.
MANAGING LAWN INSECTS UC Guide to Healthy Lawns
Good cultural practices are the primary method for managing insect damage to lawns. Growing appropriate grass species for a particular location and providing lawns with proper care are especially important. Practices such as irrigating and fertilizing have a major impact on lawn health. Physical controls, such as thatch removal, choice of mowing height and frequency, and providing grass with more light by pruning tree branches, are also important in certain situations. Naturally occurring biological control may limit some insect pests. Most home lawns in California do not need to be treated with insecticides if proper cultural practices are followed. Insecticides should never be applied unless a pest is identified and detected at damaging levels. If insecticides are necessary, choose materials that have minimum impacts on beneficial organisms and the environment.
Preventing Pest Problems
The best way to prevent damage from lawn pests is to keep grass healthy. Healthy lawns require few, if any, insecticide treatments. Also, if the turfgrass is under stress and a pesticide is applied, it stands a greater chance of suffering phytotoxic damage from the pesticide itself. The publications on managing your lawn listed in Suggested Reading give detailed information on how to grow a healthy lawn. The best way to prevent damage from lawn pests is to keep grass healthy. Healthy lawns require few, if any, insecticide treatments. Also, if the turfgrass is under stress and a pesticide is applied, it stands a greater chance of suffering phytotoxic damage from the pesticide itself. The publications on managing your lawn listed in Suggested Reading give detailed information on how to grow a healthy lawn.
Choose Appropriate Varieties
There are a number of grasses available for planting in California. These grasses are often referred to as either cool-season grasses (examples include annual ryegrass, bentgrass, fine fescue, Kentucky bluegrass, perennial ryegrass, and tall fescue) or warm-season grasses (bermudagrass, kikuyugrass, St. Augustinegrass, and zoysiagrass). Warm-season grasses produce most of their growth during summer and usually have a dormant period when they turn brown during winter. Cool-season grasses are green year-round, but produce most of their growth in spring and fall. The type of grass and the varieties within each type vary in their shade tolerance, salinity tolerance, water needs, disease resistance, and cultural needs. A formerly thriving lawn variety may decline with changes in light, such as more or less shade caused by growth or removal of nearby trees. These factors are outlined in Selecting the Best Turfgrass, listed in Suggested Reading. Selection of the appropriate grass species and variety will allow you to grow a hardy lawn with minimal maintenance inputs.
Care for Lawns Properly
Inappropriate irrigation is the most common cause of lawn damage. Overwatering (shallow, frequent sprinkling) retards deep root growth and increases lawn susceptibility to stress. Poorly maintained sprinklers can apply too much water in certain spots while underwatering other areas. Brown spots from uneven water applications occur frequently and are often caused by improperly spaced irrigation heads, sunken or tilted heads, or unmatched heads that apply differing amounts of water. Correcting these physical problems with irrigation systems can decrease water waste by over 50%, decrease water bills, and most importantly, improve the health of your lawn. Lawns should be irrigated deeply and no more often than twice a week.
Appropriate fertilization encourages a dense, thick lawn that allows grass to tolerate some insect feeding. The appropriate timing and amount of fertilizer (primarily nitrogen) varies depending on factors including season, grass species, and local growing conditions. In general, most California grasses used for lawns require from 3 to 6 pounds of actual nitrogen over a 1,000-square-foot area annually during their active growing season.
Keep the blades on your lawn mower sharp and cut your turf at a mowing height appropriate for the type of lawn grass to minimize depletion of food reserves needed to outgrow insect injury. Mowing frequency and height depend on grass species, season, and the particular use of that lawn. Cool-season lawns have suggested mowing heights of 1 1/2 to 2 1/2 inches, while warm-season lawns should be mowed to a height of 3/4 to 1 inch. No more than one-third of the grass height should be removed at one time.
Lawns also benefit from aeration. To increase water penetration and reduce soil compaction, periodically remove soil plugs using hollow tines. Thatch, which is the layer of undecomposed organic material on the soil surface, can build up and result in poor water, fertilizer, and air penetration. Thatch that is greater than 1/2 inch thick encourages caterpillar and chinch bug populations. Thatch also reduces insecticide efficacy because insecticides cannot penetrate to reach root-feeding insects. Prevent thatch by avoiding excess nitrogen application, irrigating deeply and infrequently, and minimizing the use of lawn pesticides that can reduce populations of microorganisms responsible for decomposing the thatch. If it is more than 1/2 inch thick, physically remove thatch with a garden rake, mechanical dethatcher, vertical mower, or power rake. Other methods include topdressing lawns by adding a thin layer (1/8–1/4 inch) of soil and raking or sweeping it into the thatch to encourage decomposer microorganisms. Core aerification also mixes soil into thatch, speeding decomposition.
Certain insects, other invertebrates, and microorganisms that occur naturally in lawns feed on or parasitize lawn pests. This type of control, called biological control, may help to prevent many lawn-dwelling insects from becoming pests. To protect beneficial insects, avoid using broad-spectrum pesticides that will kill them along with the pests. Biological pesticides containing organisms such as Bacillus thuringiensis (Bt) and beneficial nematodes are commercially available for controlling specific lawn insects. These materials have minimal impacts on natural enemies of insect pests and other beneficial organisms such as earthworms. Birds, moles, and other vertebrates also feed on lawn insects from time to time.
Detecting Problems in Your Lawn
Examine your lawn weekly or just before each mowing to detect problem areas. At the same time, look for weeds. A dense stand of healthy grass prevents most weeds from growing, so abundant weed growth indicates that the lawn is unhealthy and susceptible to other pests. New turfgrass is especially vulnerable to problems and has different irrigation and fertilizer requirements than established turfgrass. An indication that a lawn may be infested with insects is when the adults (e.g., moth or beetle stage) of pests are drawn to lights at night or when vertebrate predators (birds, raccoons, or skunks) are digging in your lawn for caterpillars and grubs. However, the insects coming to light may be drawn from far away and vertebrate activity is not a foolproof indicator. They may be feeding on earthworms instead of insects; also, vertebrates will return to where they previously found food, so they may dig in lawns even if insect pests are no longer abundant.
If you observe damage, the next step is to determine the actual cause. If you think the damage is caused by insects, confirm your suspicions by looking for the pest. The most accurate way to do this is by using either the drench test or by inspecting around roots (Table 2). The drench test is effective for detecting chinch bugs and caterpillars including armyworms, cutworms, and sod webworms, but it does not detect grubs. Locating and correctly identifying a pest is important because different pests require different treatment materials, timing, and application methods.
Identify the insects you find using descriptions in this publication and other publications such as Handbook of Turfgrass Pests or Turfgrass Pests listed in Suggested Reading. The UC IPM Pest Management Guidelines: Turfgrass contain color photos of some turfgrass pests. After identifying the insects, count the number of each type of insect found. Some of the insects you find may be beneficial or nondamaging. In home lawns, you usually need only to be concerned with the insects listed in Table 1.
Remember that the mere presence of an insect pest does not imply that it is the cause of unhealthy lawns or that an insecticide treatment is needed. It is normal to find a few pest insects in any healthy lawn. Generally treatments are not recommended unless the population level of the insect pest reaches a predetermined level called a threshold (Table 2). Thresholds are the population levels at which the number of insects feeding exceeds the ability of a healthy lawn to withstand the damage they cause. For example, an insecticide usually is not needed unless there are more than about 5 armyworms and cutworms or 15 lawn moth larvae per square yard. Sample several different areas of the lawn to better estimate populations overall, especially if numbers are close to suggested thresholds.
To detect chinch bugs, adult billbugs, and caterpillars including armyworms, cutworms, and larvae of lawn moths (sod webworms), perform a drench test by mixing 1 to 2 fluid ounces (2-4 tablespoons) of dishwashing liquid (such as Lemon Joy) to a gallon of water. If you are using a concentrate (i.e., Ultra) version of a dishwashing liquid, 1-1/2 tablespoons per gallon of water is adequate. Two gallons may be required where soils are dry.
Apply the solution to 1 square yard of lawn as evenly as possible using a sprinkling can. Test an area that includes both relatively healthy grass and adjoining unhealthy grass. The drench will cause insects to move to the surface. During the next 10 minutes, identify and count the number of pest insects.
Inspect Around Roots
The drench test does not indicate the presence of billbug larvae, black turfgrass ataenius larvae, or white grubs (masked chafers, May beetles, and June beetles). To detect white grubs, dig or cut beneath thatch and examine the soil around roots and crowns (where roots and stems meet). Look for the white, legless larvae of billbugs (a weevil) or the C-shaped, six-legged larvae of scarab beetles such as black turfgrass ataenius and masked chafers. When these are numerous, roots are eaten away and turf often can be rolled back like a carpet. If you find more than about one billbug larva, six white grubs, or 40 black turfgrass ataenius grubs per square foot, control may be needed.
If cultural practices are not enough to prevent damage, and a drench test or root inspection indicates treatment is warranted, choose selective, least toxic, IPM-compatible products (Table 2) whenever possible to control pests. The microbial insecticide Bacillus thuringiensis and insect-killing nematode products that can be applied like insecticides have minimal negative impacts on nontarget organisms. The insecticides azadirachtin, pyrethrum (pyrethrins), and imidacloprid are also relatively safe products for lawn insect management. Each of these products is effective only on certain pests and all must be properly timed and applied to be effective. Avoid the use of diazinon; urban use of this material has been identified as a source of pollution in California’s creeks and rivers. Other broad-spectrum insecticides, including carbaryl and pyrethroids, are available. However, these materials pose risks for beneficial and nontarget organisms. Use them only when IPM-compatible insecticides cannot control the infestation.
Avoid the use of lawn fertilizer products that also contain insecticides for preventative treatment. Insecticide treatment at the time of fertilizing is usually not justified and may reduce the presence of beneficial insects.
Mow the lawn and reduce excess thatch (greater than 1/2 inch) before applying insecticides. Unless otherwise directed on the product label, irrigate and allow grass blades to dry before treating caterpillars and other insects that feed on grass blades and stems. Do not treat if rainfall is expected and do not irrigate for at least 48 hours after spraying for leaf-feeders to allow the insecticide to remain on grass blades as long as possible. When treating white grubs and other root-feeders, wait to irrigate until after application so the insecticide is moved down into the soil.
Certain chemicals may injure lawns, especially if used on seedlings, when temperatures are too high, or if grass is stressed. Injury may also result from excess amounts, repeated applications, the wrong formulation, or from mixing incompatible materials. Inert ingredients, such as wetters, spreaders, emulsifiers, diluents, and solvents, may also injure lawns.
Bacillus thuringiensis (Bt) kurstaki.
Bt kills only caterpillars. When infected with Bt, caterpillars stop feeding within a day and usually die within a few days.
Unlike broad-spectrum insecticides that kill on contact, caterpillars must eat Bt-sprayed foliage to be killed, so proper timing and thorough spray coverage are very important. Bt is most effective on caterpillars when they are young. Once the caterpillars become large they are harder to kill with this material, and other control measures may be necessary. Apply Bt during warm, dry weather when caterpillars are feeding actively. Sunlight inactivates Bt on foliage, so make applications in the evening. Repeat treatment after about 7 to 10 days.
Insect-attacking nematodes can be applied to control caterpillars or grubs. Each nematode species is effective on a different range of pests. Select the nematode species most effective against the target pest(s) (Table 2). All nematode species are most effective when applied during the early part of the season for that pest when grubs or caterpillars are active. A second application about 2 weeks after the first increases the likelihood that nematodes will reproduce and provide long-term pest control. Irrigate before and after application. Apply to warm (at least 60°F), moist but not soggy soil. Several irrigations may be needed during the 2 weeks after each application to keep soil moist. Because nematodes are killed by light and heat, apply them in the evening, especially in hot areas.
Nematodes usually must be mail ordered. Because they are very perishable, store them as directed (usually under cool, dark conditions) and do not store them for long periods. Purchase from a reputable producer or supplier of fresh nematodes. Suppliers and more details on nematode use are available at the Ohio State University Insect Parasitic Nematodes Web site.
The botanical pesticide azadirachtin is extracted from the seeds of the neem tree. It is used to control cutworms, armyworms, and the larvae of lawn moths. Azadirachtin is absorbed by the plant and is able to move to a limited degree within the plant. Because azadirachtin acts partly as an insect growth regulator (i.e., it prevents the caterpillar from reaching maturity), most caterpillars are not killed until several days after application, and azadirachtin’s effectiveness is not immediately apparent.
Imidacloprid is a chloronicotinyl insecticide that moves systemically within plants. It is effective against black turfgrass ataenius, white grubs, and weevils. Imidacloprid has relatively long persistence. Because initial effectiveness can be delayed for days after application, it may be best to apply it during the early part of the season, when the grubs are in their earliest stages. In lawns that had damaging infestations the previous year, make treatments when adults are found in early to midsummer. If lawns are heavily infested with damaging levels of grubs later in the season, a more quick-acting, broad-spectrum insecticide may be necessary.
Pyrethrum, a botanical from flowers of certain chrysanthemums, contains pyrethrins, which are toxic to insects. Many pyrethrum products include the synergist piperonyl butoxide. Insects may only be temporarily paralyzed (knocked-down) and pests may recover from temporary effects of exposure to pyrethrum unless piperonyl butoxide is added.
Ali, A. D., and C. L. Elmore, eds. 1989. Turfgrass Pests. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 4053.
Brandenburg, R. L., and M. G. Villani, eds. 1995. Handbook of Turfgrass Pests. Lanham, MD: Entomological Society of America.
Costa, H., R. Cowles, J. Hartin, K. Kido, and H. Kaya. 2000. Insects and Mites in UC IPM Pest Management Guidelines: Turfgrass. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3365-T.
Flint, M. L., and S. H. Dreistadt. 1998. Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3386.
Harivandi, M. A., and V. A. Gibeault. 1996. Managing Lawns in Shade. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7214.
Harivandi, M. A., and V. A. Gibeault. 1996. Mowing Your Lawn and Grasscycling. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 8006.
Harivandi, M. A., and V. A. Gibeault. 1997. Managing Lawns on Heavy Soils. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7227.
Harivandi, M. A., V. A. Gibeault, M. J. Henry, L. Wu, P. M. Geisel, and C. L. Unruh. 2001. Turfgrass Selection for the Home Landscape. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 8035.
UC Statewide IPM Program. UC Guide to Healthy Lawns Web site.
Authors: S. H. Dreistadt,
UC Statewide IPM Program, UC Davis; M. A. Harivandi, UC Cooperative Extension,
Alameda Co.; H. Costa, Entomology, UC Riverside; and J. S. Hartin, UC
Cooperative Extension, San Bernardino Co.
PDF: To display a PDF document, you may need to use a PDF reader.