Do Moths Kill Grass?
Most moth species are harmless to lawns and grass. But some moth species can damage lawns and kill grass very quickly. The adults do not harm grass, but the caterpillars do. These caterpillars are commonly called cutworms, web sodworms and grass loopers. Unless the caterpillars are damaging the lawn, there is no need to do anything. If they are causing harm, they can be controlled through use of pesticides or by introducing natural predators to the lawn. Does this Spark an idea?
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Damage
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Moth caterpillars hide during the day and come out at night to feed. Damage includes bare patches, brown grass and grass blades eaten to the ground, almost as if the lawn had been scalped. There is no damage to the roots. In extremely heavy infestations, lawns will appear to move or ripple like ocean waves due to the movement of the caterpillars. Numerous small green pellets on the lawn are lawn caterpillar feces.
Pesticides
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Even if adult moths are seen near or on the lawn, do not bother trying to kill them with pesticides. They have already laid their eggs. For effective control of lawn moth caterpillars, target the caterpillars about one month after adults are seen. This will help kill newly hatched caterpillars. Spot treatment can be used instead of spraying the whole lawn, unless there is a very heavy infestation. Pesticides that kill lawn caterpillars include dimilin, halofenozide, chlorantraniliprole and broad spectrum pyrethroids.
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Caterpillar Predators
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Microscopic roundworms called nematodes feed on individual caterpillar larvae and other lawn grubs. The species Steinernema carpocapsae works best on a wide variety of caterpillars. If using nematodes for caterpillar control, do not use pesticides as these may kill the nematodes. Another option is introducing caterpillar-killing bacteria called Bacillus thuringiensis var. kurstaki.
Grass Replacement
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Some types of grass are far more resistant to moth lawn caterpillars than others, including perennial ryegrasses and fescues. These grasses are called endophytic cultivars because they contain fungi that can kill caterpillars. However, some endophytic cultivars may sicken grass-eating animals, so be sure that grazing animals do not have access to the lawn. Seeds from endophytic cultivars have been purposefully infected with fungi in order to grow the caterpillar-killing grass. It will also kill chinch bugs.
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