You first notice a small patch of dying grass here, then one there. They then get bigger as the summer goes on. Chances are, you're dealing with grubs, the tiny, white, C-shaped larvae of various beetle species. These root-feeding creatures are among the most devastating pests of lawns, but they're not invulnerable to grub-controlling pesticides. The key to controlling grubs with pesticides is proper timing.
Understanding the Life Cycle
White grubs are the larvae of Japanese beetles, European chafers, May beetles, June beetles and other scarabs. Most white grub species have a similar life cycle: adults emerge from the ground, breed and lay eggs between June and August. Eggs hatch into tiny grubs that begin feeding near the soil surface. The best time to control grubs is when they are young and feeding near the soil; it becomes more and more difficult as they become larger.
Preventing a grub problem before it starts saves you the hassle of trying to get the perfect timing for emergency applications later in the year. Preventive control also has more slack in the time frame. The best time to apply preventive grub control is during the month before the eggs hatch up until the very small, young grubs are present. However, the University of Kentucky College of Agriculture, Food and Environment suggests that applications made in May should have enough residual left to control grubs that hatch in July and August.
Carbaryl and trichlorfon are two chemicals found in curative treatments. Products vary, but in general: Apply trichlorfon granules at a rate of 2 pounds per 1,000 square feet; apply carbaryl granules at a rate of 9 pounds per 1,000 square feet. Read the label to double-check application rates and ensure correct spreader settings. Curative chemicals don't have the long life in the soil that preventive products do. Michigan State University Turfgrass Science performed a study on various grub controls; the results showed that 20 to 80 percent of grubs were killed when curative products were applied in September. The key is to apply the curative insecticide before the soil temperature drops and the mature grubs begin moving deeper into the soil.
Make sure the grass is dry and soil is not waterlogged or excessively wet before applying; do not apply during particularly humid weather. Before applying any chemicals, mow your lawn and rake the thatch layer to ensure the spray or granules penetrate deeper into the soil. Thatch is the thick layer of dead grass that lies between the green turf and soil. No matter whether you're using a curative or preventive approach, always water the insecticide into the soil approximately 1/2 to 1 inch deep. If you have problems with grubs this year, use a preventive grub control next year to curb the process.