Lawn grubs are the larvae of many types of beetles. They are commonly found below the grass surface and like to feed on grass roots, killing grass and turning it brown, often in late summer and early fall. There are a number of solutions to kill grubs and different ways in which to prevent their appearance.
Milky spore is a natural, chemical-free bacterial remedy to kill grubs. Granules or powder are spread on soil, causing the grubs to catch a disease that kills them. Milky spore affects only the grubs and beneficial organisms remain. One treatment can last many years as the bacteria multiplies over time and sits inactive, waiting for the grubs. Milky spore is resistant to bad weather and it is compatible with other lawn chemicals such as fertilizers and pesticides. It is also safe for children and pets and for use around ponds and streams.
Nematodes are another biological method for controlling and killing grubs. As very small parasitic worms, their eggs are microscopic and come on a small sponge, approximately 1 million at a time. Mixed with water and applied to the soil to hatch, nematodes work by searching for grubs, entering them and releasing a bacteria that kills them. Nematodes should be applied to lawns late in the day and watered immediately after. They are available at garden stores. They are often sold as Hb nematodes. These, too, are harmless to humans and pets.
The best time to control grubs is in late July to mid-August, while they are small and close to the soil surface because this is when they tend to feed. There are a number of chemical insecticides on the market that have been developed to control grubs with their residue, so they can be applied in June or July. One example of an insecticide is Merit. Trying to control grubs outside of the summer season, such as in early spring or late fall, is difficult because grubs are large and may not be feeding at this time. Trichloron and Carabaryl are insecticides made for this instance. Keep in mind that it is necessary to water the lawn thoroughly after an even application of insecticide.
Preventing grub damage can be done naturally. Healthy lawns can actually support many insects without incurring noticeable damage. Mow the grass at a height of about 3 inches to keep roots healthy. Compacted soil can be aerated to encourage deep root growth. Water grass deeply to allow for deep root growth, as well. Kentucky Bluegrass is one of the grub's favorite grass roots, so limit this type of grass.