It is important to accurately identify insects found in turfgrass stands because many of them are not pests. In addition, the most effective treatment for one pest may not satisfactorily control another. Lawns tolerate moderate levels of most insect pests and insecticide treatments are infrequently needed in California. Be sure that insects are present at damaging levels before applying insecticides (see table below).
To detect cutworms, sod webworms, southern chinch bugs, fiery skipper larvae, and billbug adults, use the drench test. To carry out this test, mix one to two fluid ounces of liquid dishwashing soap in 1 gallon of water. Apply the solution to 1 square yard of turf as evenly as possible using a sprinkling can. This will irritate the insects so that they move to the surface within 10 minutes. Use the descriptions in these guidelines to accurately identify the insects. White grubs (larval stages of masked chafers, May beetles and June beetles), black turfgrass ataenius larvae, and billbug larvae will not respond to the drench test. 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.
In large lawn areas such as parks, golf courses, and cemeteries, monitor several locations to determine the extent of an infestation. Certain pests, such as white grubs, often repeatedly infest limited areas where adults prefer to lay their eggs. If problems are localized, spot treatments may be suitable. Don't treat for insect pests unless treatment thresholds are exceeded as indicated in the following table.
|Insect||Detection method||Treatment target||Suggested treatment threshold|
|armyworms, cutworms||use a drench test to look for fat, dull gray, green, or brownish larvae up to 2 inches long; inspect outdoor lights around dawn for 1-1/4-inch brownish to gray moths||crowns, leaves, thatch||5/yd2|
|billbugs||dig around roots for whitish, C-shaped, legless grubs up to 3/8 inch long with reddish heads; inspect outdoor lights around dawn for 1/3 inch brownish to gray snout beetles||crown, roots||1 to 10/ft2 varies with turf species and climate*|
|black turfgrass ataenius (see also white grubs)||dig around roots for whitish, C-shaped grubs up to 1/3 inch long with 6 legs and reddish heads; inspect outdoor lights around dawn for shiny black adults 1/5 inch long||roots, thatch soil interface||40/ft2|
|chinch bug, southern||drench test or inspect around grass bases for reddish, purple, black, or gray bugs up to 1/2 inch long||crowns, stems||135/yd2 or 15 nymphs & adults/ft2|
|lawn moths (sod webworms)||drench test for slender, grayish larvae up to 3/4 inch long; whitish or brownish moths up to 3/4 inch long fly when grass is disturbed||crowns, leaves, thatch||15/yd2|
|skipper, fiery||drench test for larvae up to 1 inch long with pink-green body and red and black head; orangish butterflies 1 inch wide with knobbed antennae feed at flowers; mere presence of this insect does not warrant control||leaves, stems||15/yd2|
|white grubs (the immatures of masked chafers, May and June beetles; see also black turfgrass ataenius)||dig around roots in late winter or summer for whitish to yellow, wrinkled, C-shaped grub up to 1-1/2 inches long with 6 legs and a reddish head; look for yellowish brown adults 1/2 inch long||roots||6/ft2|
|*Threshold for application of curative insecticides. Preventive treatments (e.g., imidacloprid and other neonicotinoids) applied early season when adults are laying eggs are often most effective where grubs are a regular problem in high value turf.|
Vigorous turfgrass on most California lawns, school playing fields, and parks has few insect problems, and insecticide treatments are infrequently needed and only when monitoring indicates that damage thresholds have been exceeded. More intensively managed turfgrass such as golf courses, putting greens, and professional sports fields tend to have more insect problems and are treated more often.
Before applying a treatment for foliar or thatch-dwelling pests, irrigate the turf well and then treat as soon as the plants dry. Apply the required amount of insecticide in enough water to thoroughly wet the grass down to the ground; for foliage feeders such as the fiery skipper, sod webworm, armyworms, and cutworms, 2 to 5 gallons of water per 1,000 square feet of turf works well. The bermudagrass mite as well as the root-feeding pests (billbugs, black turfgrass ataenius) require a greater volume of water (25 gallons per 1,000 square feet) to move the pesticide into the area where the pest is feeding. Insects that feed in the thatch layer (southern chinch bug) should have treatments applied in 10 to 25 gallons of water per 1,000 square feet of turf. Do not irrigate following a chemical application until necessary to prevent wilting; this will allow the insecticide to remain on the plants for the longest possible period. Do not apply insecticides when temperatures exceed 90°F or to water-stressed dichondra.
When applying parasitic nematodes, irrigate before and after the application. In addition, soil temperatures must also be above 60°F when applying nematodes. During hot weather, apply nematodes in the morning or late evening and irrigate every few days for 2 weeks after the application to keep the soil moist, but not soggy. When treating for pests that feed below ground on grass roots, irrigate following application.
In general, sprays work best when treating foliar turfgrass pests, but granular formulations are acceptable for controlling white grubs, billbugs, chinch bugs, cutworms, skipper larvae, and sod webworms. Granules are advantageous when attempting to control pests residing in or below the thatch layer because they move past leaf blades and partially penetrate the thatch layer. However, granular insecticides are often a second choice relative to wettable powders or emulsifiable concentrate formulations because they do not work as fast and because of accidental ingestion by birds. Special care must also be taken to assure granules do not remain on hard surfaces and get washed into storm drains.
To help prevent the development of resistance to a pesticide, rotate pesticides with different mode-of-action group numbers. These numbers are listed with each pesticide in the treatment tables throughout these guidelines.
Predators and parasites of turfgrass pests are disrupted by broad-spectrum insecticides such as pyrethroids (e.g., cyfluthrin), carbamates (carbaryl), and to a lesser extent, organophosphates (e.g., acephate) and imidacloprid. Alternatives such as spinosad, insect-pathogenic nematodes, and Bacillus thuringiensis (Bt) control a narrower range of organisms, thus preserving naturally occurring beneficial insects. The pathogenic nematode, Steinernema carpocapsae, applied to control cutworms and black turfgrass ataenius may be as effective as some conventional insecticides, but timing the applications correctly is critical to their effectiveness. Because nematodes are killed by light and heat, make applications in the evening, especially in hot areas and sunny locations. Bt products are typically inexpensive, but timing is also very critical for achieving control; use of this material requires additional scouting. The additional material expense of nematodes or effort involved in scouting when using Bt has the ultimate payoff in allowing natural enemies, such as scoliids and tiphiids (white grub parasites) and adults and nymphs of bigeyed bugs (Geocoris), to remain part of the turf system. (Nematodes must usually be mail ordered. They are perishable, so store them as directed by the label. For more information on using entomopathogenic nematodes and other biocontrol effectively, see Natural Enemy Releases for Biocontrol of Crop Pests.