Managing lawn and turf insects
- Identification: properly identify the insect
- Damage: distinguish between insect damage and turf disease
- Scouting: find the insect
- Management: use IPM principles
- Root feeding: white grubs, weevil larvae
Identification: properly identify the insect
Detecting the presence of an insect is the first step in good insect control. When you find the insect, examine it closely to identify it to species.
Damage: distinguish between insect damage and turf disease
If the turf looks damaged, wilted, and water-starved, then an insect may be involved. During root feeding, insect species that feed on roots detach the thatch and blades from the roots and permit the sod to peel off the soil without any root attachment. In addition, some insects defoliate or suck the grass blades. You must search in the blades and thatch to find these insects. Blade defoliation damage appears as brown scars where the blades are clipped off by the insect. Blade sucking damage appears as brown lesions where the blade's sap was removed by the insect. Many times an area of turf is brown and damaged, but damaging insects cannot be found. Search for the insects along the margin of brown and green grass.
When turf damage is noticed and before applying pesticides, make sure insects and not diseases or some abiotic factor are the cause of the damage. Turf damage may be caused by fungal diseases, abiotic conditions, and improper maintenance. See University of Minnesota Extension bulletins: Turf Patch Diseases; Watering Lawns and Other Turf; and Weed Control in Lawns and Other Turf.
Scouting: find the insect
Be sure to examine an area of turf that contains living as well as damaged grass. The most serious insects of turf feed on living turf and are not found in dead areas. Insects found in completely dead patches generally are not responsible for the damage. Methods are available for discovering insects in turf. Cutworms, sod webworms, aphids, chinch bugs, and other blade defoliating and blade sucking insects can be detected by the flotation method. Use a large coffee can with both ends removed and sink it into the turf. Mix one ounce of liquid dish washing detergent into one gallon of water and pour the soapy water into the container. In a few minutes, the soapy water will irritate the insect, the insect will release its grasp, and the insect will float.
Root-feeding insects such as white grubs and billbugs will not respond to the flotation method. Grubs feed by separating grass blades. Billbug larvae are legless and live inside the grass sheath and do not separate blades from roots until the last larval stage (instar). Sample grubs and billbugs by looking for insects in grass roots and in the soil layer beneath the roots. If infestations are heavy, the grubs will have removed most of the grass roots and the turf will roll back like a carpet.
Management: use IPM principles
Integrated Pest Management (IPM) is a decision-making process that includes scouting, damage threshold, control options, and timing of insecticide application. IPM practices conserve beneficial insects and promote pesticide usage at the vulnerable stage in the pest's life history.
Steps in IPM:
- Routinely inspect or scout the turf.
- Determine changes in cultural practices that can increase turf health and vigor.
- Determine what is an acceptable threshold of pest damage.
- Time the pesticide application to the vulnerable stage in the insect's life history.
- Return to step 1. Begin inspecting.
First inspect your turf for damage or insects. This is called scouting. Look for discoloration, defoliation, and separation of grass from roots. When investigating turf damage, pay particular attention to whether the damage spreads.
After detecting insects, the next step is to determine if the insects are pests, harmless, or beneficial. Only pest insects warrant treatment. Thresholds have been established for some turf insects. Thresholds are the maximum number of insects per specified area that can be tolerated without obvious turf injury. Often thresholds are general and not specific guidelines, because other factors influence damage, such as drought, grass cultivar, and traffic and compaction of the grass. For example, heavily fertilized golf courses usually contain the most insects.
In Minnesota, most home lawns occasionally need chemical management for insects. Fungi cause more damage than insects. For those instances when insects are damaging the turf, suggested pesticides are given at the end of this bulletin.
After locating the damaging insect, time insecticide usage to the vulnerable stage of the pest. Insects are often more susceptible to treatment in a certain stage in their development, often when the immatures are actively feeding. Also, the judicious use of conventional insecticides helps preserve beneficial insects that naturally regulate pest insects. Applying scheduled sprays, without determining if the insect is present, can lead to expensive pesticide applications, create pest populations resistant to the pesticide, and disrupt the natural control by beneficial insects in the turf.
Note to homeowners: A robin icon indicates the insects described below can be found in household lawns in Minnesota. All pests can potentially be found on golf courses and athletic fields.