Insects are not a common cause of residential lawn damage in California, but certain species occasionally damage or kill grass. 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 mask chafers; billbugs, which are weevils with white, grublike larvae; and chinch bugs. Each species produces somewhat different damage symptoms and must be managed differently. Study Table 1 for damage symptoms associated with each pest. 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.

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 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.

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 between 3 and 6 pounds of actual nitrogen annually during their active growing season.

Keep the blades on your lawnmower 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 1/3 of the grass height should be removed at one time.

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 the lawn is unhealthy and susceptible to other pests. New turf is especially vulnerable to problems. 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, and skunks) are digging in your lawn for caterpillars and grubs. However, 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.

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. Thresholds are the population levels at which the number of insects feeding exceeds the ability of a healthy lawn to withstand the damage.

If cultural practices are not enough to prevent damage, and a drench test or root inspection indicates treatment is warranted, choose selective, least toxic products 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 non-target organisms. The insecticides azadirachtin 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. While the organophosphate insecticides chlorpyrifos and diazinon are also registered for treatment of insects in home lawns, these broad-spectrum materials should be avoided because of problems associated with runoff in urban surface water, contamination of municipal waste water, and impacts on non-target organisms. 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.

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