Lawn Insect Management

Insects are not a common cause of residential lawn damage, 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 fertilizers and herbicides, and dog urine also produce damage resembling that of insects. Before taking any insect control action it must be determined that it is insects  causing the problem and not something else.

Insects that may cause damage in New England lawns are given in the Table.  Each species produces somewhat different damage symptoms on differect hosts and must be managed differently. In addition to the pests in this Table other insects may be observed while examining grass. However, control is rarely or never needed for most types of insects because they are beneficial. Common beneficial “insects” include ants, ground beetles, rove beetles, spiders (not an insect), and ants.

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. 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.

Biological Control

"Biopesticides" (living organisms which are handled and applied in a manner similar to traditional insecticides) or other biological control agents reduce dependence on traditional insecticides. Examples include entomopathogenic nematodes, bacteria, endophytes, and fungi.

Nematodes: Entomopathogenic nematodes carry bacteria inside their bodies. When the nematode penetrates an insect victim, it releases bacteria, which break down the internal tissues of the target insect, resulting in a massive infection. As the insect dies, the nematodes reproduce within the cadaver. The juvenile nematodes pick up some of the bacteria, and move on in search of new target insects. 

Identifying Features of Various Lawn Pests

Entomopathogenic nematodes are available commercially and appear to be effective at suppressing populations of several lawn insects insects. The most common commercially available nematode is Steinernema carpocapsae, available under a variety of trade names and formulations. This nematode appears to be effective against webworms and cutworms.

Bacteria: Some bacteria cause diseases in insects. The most common bacterium used against turf insects in Bacillus  thuringiensis var. kurstaki, or "B.t." It is effective against several kinds of caterpillars and can be used as a foliar spray against caterpillars like the gypsy moth as well as cutworms and webworms in lawns. It should be applied when the target caterpillars are still relatively small (less than half an inch). Bacillus popilliae causes "milky disease" in Japanese beetle grubs. Infected grubs take on a very milky appearance and are very flaccid. Use of milky disease in New England is somewhat controversial, because there are no data to indicate whether the disease actually suppresses grub populations. If the disease becomes established, it usually takes a few months to have a noticeable effect on the grubs in the area, but may remain "active" for three to five years in that area. Milky disease is available commercially as Milky Spore.

Fungi: Some fungi cause diseases in or on insect bodies and several such fungi occur naturally in New England. One of the "native" fungi is Beauveria bassiana, which attacks chinchbugs and billbugs in lawns. Another fungus, Metarhizium anisopliae, appears to be quite effective against white grubs in the soil. The main challenge is to find a way to "package" the fungus so that it is not sensitive to sunlight and can be applied through conventional application equipment. It is, therefore, not available commercially. 

Endophytes: Finally, there are some species of grasses which contain endophytes, which are fungi that produce substances which are toxic to certain insects. Endophytes occur naturally in some perennial ryegrasses and fescues, and have been incorporated into some commercial cultivars. They are effective in the suppression of chinch bugs and billbug populations, and are active against cutworms and webworms as well. [Note that endophytes are toxic to grazing stock, such as sheep and cattle, and so should not be used in pasture settings.]

Source: Adapted from the University of Massachusetts Extension, 1999; University of California IPM Program