During May, we begin to see the adult May and June beetles flying around lights or onto window screens, usually at night. The female May beetle deposits eggs into the turf from April through May; whereas the June beetle deposits eggs from May through June. The eggs hatch into grub worms that are creamy white in color with brown heads. The grubs feed on dead organic matter and then move to the roots of plants. Since grubs feed on roots, they can injure roots of grasses and other plants. This causes infested turf to turn brown and become removable in large clumps.
Before treating for grub worms, lawns should be inspected to determine the presence of an infestation which is more than five grubs found within a square foot. To inspect an area, take random soil sections 3 to 4 inches deep for a total of 1 square foot for every 1,000 square feet of infested area. One square foot of turf can be sampled by removing four, 6-inch square pieces of turf or 10, 4-inch cup cutter core samples.
The optimal time for inspection and treatment is five to six weeks after beetles are seen. This will ensure that smaller grub worms will be found in the turf. Apply insecticides only if a grub worm infestation exists in your lawn, since unnecessary use of insecticides can cause insect resistance and harm to beneficial organisms.
Non-Chemical Control Options:
- Maintain healthy turf by fertilizing and watering properly.
- Parasitic nematodes in the genera Steinernema and Heterorhabtitis have been shown to be effective against white grubs. They can be purchased and applied to infested areas.
Chemical Control Options:
- Irrigating the soil with ¼ to ½ inches of water prior to treatment can improve the effectiveness of the insecticides, since the grubs will move closer to the soil surface.
- Imidacloprid, halofenozide, and clothianidin are some chemical options that are often applied before extensive grub worm damage is seen, since they are effective on smaller grub worms. Lambda-cyhalothrin and trichlorfon are some examples of chemicals used after grub worms are present as a curative control. Also there are combinations of chemicals such as imidacloprid and bifenthrin that can be used for a preventative and curative control option.
Source: AgriLife Extension, Texas A&M University
