Michelle Marquis of Santa Rosa asks: My lawn has a few dead spots about 2-3 feet in diameter. I checked the soil to see if it was dry, then dug into these dead spots and found a few ugly, fat, grayish-looking, curled up worms. Can you tell me if these bugs could be causing this problem?
They sound like you're describing white grubs. They are in the immature life stage of one of many different beetle species. White grubs can vary greatly in size, depending on species, from a ? inch to the size of your thumb. They usually stay curled up in a "c" shape and are white to cream in color. They have brown heads and six legs. Most of these grubs feed on the roots of grass. This results in yellowing or browning of the grass, making it easy to pull up, and since they're eating the roots, they kill the grass. There could be additional damage when mammals like skunks, birds or even moles dig up the lawn looking for these grubs to feed on.
Before you treat, be sure the grubs are the actual cause of the problem and the dead grass is not due to lack of water, chinch bugs or disease. The best way to find out if there are grubs that are doing the damage is by digging. Cut three sides of a 1-foot square and roll the grass back. Dig around in there a bit. If you find high numbers of grubs, such as 10 or more, then treatment may be necessary. If only a few are found, say, around 5 grubs or less, then treatment isn't necessary. If you count around 6 to 9 grubs, keep an eye on the grass for additional spots developing because the population may go down naturally and you still won't have to treat. When you're finished investigating, roll the grass back, tamp it down and water it, and it'll continue to grow.
If you find that you need to take action, using beneficial (entomopathogenic) nematodes is a safe and organic way to go to control lawn pests. These can be purchased from nursery centers that specialize in organic products. They're safe to use around humans and pets. Nematodes are the most numerous multicellular animals on Earth! There are many thousands of individual nematodes in every single handful of garden soil! They're so small, you can't see them with the naked eye — you need a 10X hand lens. So every time you dig in the soil, you're touching these little guys. But what are they?
Nematodes are microscopic nonsegmented worms that can be free-living, predaceous or parasitic. You could look at them as being good, bad or indifferent. The bad nematodes parasitize roots of plants, cause foliar damage or even be parasites of mammals. The indifferent ones just hang out in the soil feeding on things like bacteria and fungi. The good guys are the nematodes that are used in biological control to combat many different insect pests. These are the entomopathogenic nematodes.
In the commercial market today, there are several species of beneficial nematodes available at specialty nurseries and through the Internet. They can be used to control grubs, fleas, weevils, and many other insect pests. The insect pest must spend part of its life cycle in the soil, where the nematodes are applied. So it's very important to know what your pest is before you can properly treat the problem. Before you order nematodes, talk to the supplier and find out what species of nematode is right for you and your insect problem. Beneficial nematodes can be an excellent tool in the lawn and garden to control many pest insects. They can be used with organic gardening.