Description

Grub worms have had a good year. It's true that these are the immature stage of beetles. In most cases either Japanese beetles or green June beetles. Both of these insects have one generation per year. After the beetles mated this summer, they laid eggs, quit flying around, and died. Soon after, the eggs hatched. The larvae of these beetles, known as grub worms feed in the soil during the warm days of fall. As the soil temperature falls, they burrow deeper to spend the winter. Depending on the weather they may be higher and lower in the soil until spring when it warms. Then they will be back up near the surface and feeding on grass roots again. By early summer they are pupating to emerge again as flying adults.

Japanese beetles when exposed tend to curl up in a C shape. Green June beetles stretch out on their backs and wiggle along. In the soil these beetles may damage lawns by feeding on roots. If there are large numbers, insecticides may be necessary to control them. During the early days of fall when they are close to the soil surface (and before they have damaged the lawn), is the optimal time to treat. With recent cool wet weather, they may be deeper than insecticides will reach. If the numbers are great (more than 5 per square foot), you may have success treating them after another warm spell. Dig up a square of lawn to see how deep they are. If more than 2 inches down, don't bother. The next best time to treat them is next spring when warm weather brings them to the surface. By then, however, they have done most of their damage; and they're big enough to require heavier doses of insecticides.

Milky spore disease is a slow but effective (sometimes) control when applied on a community wide basis. It may take several years to be effective. And since the adults can fly up to half mile or more to lay eggs, there's not much value in using that approach on a single lawn.