Active insect pest infestations on managed turfgrass sites pose a persistent and difficult challenge to professional turf managers and homeowners alike. Successful management strategies combine a thorough working knowledge of the environment and the biology of the grass species with a good understanding of insect pest distribution, insect life cycles, identification characteristics, plant symptomology, correct scouting techniques, and appropriate cultural and chemical control strategies.
Recognizing Insect Damage in Turf
Perhaps the most difficult task in correctly diagnosing damage caused by insects in turfgrass is the process of differentiating insect damage symptoms from those produced by turfgrass diseases or other problems (temperature, drought, soil compaction, etc.). Because many of the site and plant symptoms generated by non-insect activities closely resemble those caused by insects, the best way to make an accurate diagnosis of insect damage is to have a thorough understanding of the multiple ways these similar symptoms can be produced. For managers who are often faced with multiple grass species at different sites under varying conditions, reaching an accurate diagnosis is a matter of consistently applying a system designed to narrow down the possibilities. The following five questions can help managers differentiate the causes of damage at turfgrass sites.
- Do the symptoms have a regular or definable pattern, such as stripes, circles, or tracks? If so, then look at mechanical activity, such as mowing, traffic, or drainage as a possible cause.
- Does the site show signs of animal activity or damage, such as birds feeding or turf torn up by skunks or raccoons? If so, then look for insect activity in the damaged areas.
- Did the symptoms appear after a prolonged period of warm temperatures, high humidity and evening thunderstorms? If so, then consider disease activity.
- Does an examination of plants in affected areas show any identifiable insects or leaf, crown, or root disruptions? If not, then consider the site’s other management practices, such as misapplication of fertilizers or pesticides, as the possible cause.
- Does examination of the affected plants show signs of feeding activity, such as damaged leaves, crowns, or roots or evidence of chewed plant material (frass) at the base of plants? If so, then, insects are the likely cause.
Insects are responsible for a significant amount of damage to turf every year. A good turf manager should ask:
Where on the plant does the insect damage occur? With surface shoot and leaf-feeding insects, turf damage is readily apparent because leaves and stems are chewed off or leaf yellowing appears. For subsurface root-feeding insects, you generally don’t detect turf injury until after the pest has done the damage. This is why grounds managers must be constantly vigilant for these pests and ready to take action before the pest becomes a problem. Preventative, systemic insecticides may be the best answer for insects with a track record of damage or for high value turf.
What type of bug is damaging your grass and where is it in its life cycle? Grubs and caterpillars are the main culprits behind insect damage to turf and landscape plants. Both are insects in their immature stages. Grubs are the larval stage of insects of the Coleoptera order. Grubs that damage turf primarily belong to the Scarabaeidae (beetles) and Curculionidae (weevils and billbugs) families. Most of the damage that grubs cause centers on roots. Weevils and billbugs are an exception, because their larvae live in and feed on shoots for most of their larval stage. Caterpillars are the larval stage of insects of the Lepidoptera order (butterflies, moths and skippers). Caterpillars are primarily shoot- and leaf-feeding insects.
When is the best time of year or stage of the insect’s life cycle to attempt control? All insects grow and develop through a process called metamorphosis. Insects exhibit either simple or complex metamorphosis. Simple metamorphosis occurs in species such as chinch bugs, aphids and mole crickets. It entails three stages: egg, nymph (immature adult), and adult. Complex metamorphosis involves four growth stages: egg, larva, pupa, and adult. Grubs and caterpillars are the larval stages of insects that develop through complex metamorphosis. Larvae feed voraciously. The pupal stage is the resting stage between larva and adult. During the pupal stage, an insect does not feed and is incapable of locomotion. However, major structural reorganization occurs during pupal stage as the insect transforms from a larva into an adult.
How should insects be controlled? Insecticides are one obvious tool to help you keep insect pests in check. Your challenge is to know which chemical will be most effective, how and when it can effectively be used, and what impact it will have on your overall program for effective control. For example, natural predation of the big eyed bug on chinch bugs in Virginia will, in most cases, suppress chinch bugs from causing visible damage. Indiscriminately using broad-spectrum chemical insecticides will adversely affect beneficial predators, such as the big eyed bug. As new selective insecticides are developed and released, they will give turfgrass professionals and homeowners an additional means of control. For successful insect control, the turfgrass manager must rely on an integrated program. This type of control strategy will result in better control at less cost and with greater environmental safety.