If your lawn is starting to show signs of illness--from brown spots to roots disappearing and loosening the grass--you might have an insect problem. There are a number of insects that can destroy a lawn, and they can all be a definite nuisance. It's vitally important to determine which insects are causing the destruction before it's treated, and it's equally important to diagnose quickly.
There are a handful of different varieties of these small weevils, but the damage they cause is the same, and looks like it could be caused by a number of other problems. Billbug damage is nondescript, manifesting itself as brown spots in the lawn. The bugs themselves are small, only about a quarter of an inch long. Dark gray or black as adults, they are white as larva. Billbugs hibernate during the cold winter months, then emerge in the spring to feed. Eggs are laid in the summer inside grass stems, and when the larva hatches they feed on the grasses. Eventually the new billbugs leave the grass stems--usually in late summer or early fall--where they begin the hibernation cycle all over again. Billbugs can be among the hardest lawn pests to control, because they do not ingest much insecticide when young, as the larva begin life inside grasses. Some grasses are resistant to billbugs, and since the insects rarely fly, it isn't a given that an attack in one area of a neighborhood will spread throughout.
The name of the armyworm is deceiving, as the adults are actually moths. However, it's the caterpillars that do the most damage as they consume the plants around them in preparation for their transformation into moths. The first part of their name comes from their tendency to move through an area in a colony, or army. The moths are small and nondescript, tan with a white dot on each wing. Their food of choice is nectar and fruit. The caterpillars can reach up to 1 1/2 inches in length when mature, and are typical green or brown with lighter stripes. Caterpillars feed mostly a night, so that's generally the best time to apply insecticide. Damage will occur as chewed grasses usually in a circular, depressed area, and oftentimes by the time damage is apparent it's too late to control the caterpillars. One way to help control the population is to mow lawns short to make them less appealing.
White grubs aren't only among the most widespread of lawn insects, but they're also some of the most destructive. The larval stage of beetles like the May/June beetle and the Japanese beetle, white grubs feed on the roots of grasses. Early signs can manifest themselves as yellowing grass, and later the grasses become loosened from the soil and can be peeled back. The species of white grubs can be difficult to identify, as the biggest difference in them is a slight difference in size. Depending on the species, the beetles can have one or more generations per year and wreak havoc on a lawn throughout the whole growing season.
Fortunately, one of the white grubs' deadliest enemies can also be one of your best allies--the bird. A tasty meal for almost any bird, attracting these feathered friends to the yard can greatly impact the grub population. Chemical control can also be used, but beginning with a low strength insecticide.