There are 2 main types of grubs that attack and damage lawns: The European Chafer Beetle and the Japanese beetle. They normally hatch mid to late July and begin feeding right away and continue into late fall (depending on soil temperatures). After maturing below the frost line over the winter, they reappear in early spring to feed for about for about 4-6 weeks before pupating. After changing into adults (late June), they will emerge to mate.
By feeding on the roots of grass grubs weaken the plants ability to draw up moisture, in turn damaging the turf. Signs of grub infestation are seen as sporadic irregular brown patches. These patches lift up easily because of the lack of root system. Small animals such as raccoons, skunks and birds cause more damage because the dig for grubs.
Defending your lawn against grubs is an ongoing maintenance practice. Healthy lawns need irrigating, mowing, fertilizing and aeration (when needed) thus creating a lush thick turf which is more intolerant of infestation. However, even the best of lawn maintenance, populations over time can become serious enough to seek help.
Parasitic Nematodes are a “natural insect parasite” that effectively control soil dwelling and boring larvae (European chafer, Japanese, Asiatic, May/June beetles). Nematodes actively search for larvae and enter a natural body opening, sometimes directly through the skin. Once inside the larva the nematode excretes specific bacteria from its digestive tract before it starts to feed. The bacteria multiply very rapidly and convert the host tissue into products that the nematodes take up and use for food. The larva dies within a few days and the color changes from white-beige to orange-red or red-brown. The nematodes multiply and develop within the dead insect. As soon as the nematodes are in the infectious third stage, they leave the old host and start searching for new larvae. When there are no new hosts present, the nematode population will slowly decrease. They will migrate through your lawn as long as they have water channels to move(lawn irrigation). Usually 2 applications are needed in order to address the life cycle of the beetles. Soil temperatures must be between 14-33C for development. They will become dormant in colder conditions and because they cannot tolerate freezing temperatures they die with the frost. The most reliable time to estimate optimal application period is to note when the first adult beetles are seen flying.