Take control of grubs in your lawn

June 19, 2007

University Park, Pa. -- Got grubs? Reluctant to spray pesticides on your lawn, but don't know how else to get rid of them? The Pennsylvania IPM Program has advice for safe and effective alternatives.

According to Michelle Niedermeier, community integrated pest management (IPM) coordinator with PA IPM, a collaboration between the Penn State and the Pennsylvania Department of Agriculture, white grubs are immature scarab beetles such as Japanese or Oriental beetles. "Grubs live in the soil eating plant roots, so you may not be aware of them until you see damage."

In late June and early July, Japanese beetles emerge from the soil in search of food and mates. They feed on a variety of plants, including roses, grapes and linden trees. In July, females will lay up to 60 eggs in the soil, with first eggs hatching about two weeks later. "The grubs are small and feed close to the surface, causing visible damage from August to October as they molt and consume more roots," said Niedermeier. "Look for large, irregular patches of brown turf that easily peel away from the soil. As temperatures drop in the fall, grubs will move down into the soil, below the frost line before moving up in the spring closer to the heat in order to form pupae, a nonfeeding stage that transforms the grub into a beetle."

Homeowners who suspect grubs are wrecking havoc on their lawn should try using an integrated pest management (IPM) approach. "IPM 'integrates' many management tactics for more effective pest management results," Niedermeier explained. "If pesticides must be used, only the least toxic products and formulations are chosen. IPM focuses on pest prevention by understanding pests' habits and needs and removing conditions conducive to the pests."

To make sure the lawn has grubs and not some other pest or disease, sample a one-foot section of the lawn in late summer. Niedermeier says dig a hole or use a bulb planter to remove a core of the soil and grass. "Look for grubs and count how many you find. If you find less than five, you probably don't need to worry. But if you find more, consider treating them, especially if your lawn is stressed."

If the lawn needs to be treated, do it in the late summer or early fall when grubs are small and actively feeding close the surface using a natural approach first. "Milky spore disease is a nontoxic way to control grubs. The spores are applied to the lawn, and grubs are infected when they feed on the thatch or roots of treated grass," Niedermeier explained. "The grubs die and disintegrate and release up to 2 billion spores back into the soil; however, it may take a season or two before there is significant impact."

Spraying beneficial nematodes in affected areas in the fall is a safe, effective way to control grubs. Nematodes are microscopic, soil-dwelling worms that actively search for pre-adult insects like grubs. After invading the body of the grub, the nematodes release a bacterium that infects and kills them. Nematodes come in a liquid that can be sprayed with regular garden sprayers. However, if chemicals were used in the sprayer previously it could kill the nematodes, so be sure to carefully clean it before use. Since nematodes are alive they need to be used soon after purchase. Follow the directions carefully for maximum efficacy. Beneficial nematodes are sold under the trade names NemAttack, NemaSeek and TerraNem.

Another alternative is neem oil, a botanical pesticide. Extracted from the tropical neem tree, neem oil contains insecticidal properties and can act as a repellent, deterring feeding, insect growth and egg laying. Mix the neem oil with water as directed on the label and spray the diluted solution generously on affected areas.

Niedermeier said to avoid using large amounts of pesticides in the spring that promise to protect the awn for six months. "Such promises indicate that the product actually kills many types of insects and lasts for a long time in the environment. Additionally, grubs are less susceptible in the spring, especially after forming pupae," Niedermeier explained. "Also, spring rains on young lawns can wash pesticides off and down storm drains leading to streams, increasing the chance of water pollution."

No matter what lawn plan is used, Niedermeier said to read labels on products and follow directions exactly. "Even though botanical pesticides are derived from plants, it doesn't necessarily mean they are safe for humans and other mammals." Milky spore disease, beneficial nematodes and neem oil can be purchased online and at some garden centers and home improvement stores.

Niedermeier said that once the damage has been done, try compensating for lack of roots by replanting damaged areas and watering the lawn. Keep the lawn healthy by not mowing too short, keeping grass length at about 2 to 3 inches and never removing more than 1/3 of the blade length at a time. Also, avoid over fertilizing; always apply fertilizer in recommended amounts when grass is dry and water thoroughly after application.

For information on grubs and lawn care tips, visit PA IPM's Pest Problem Solver on the Web at http://paipm.cas.psu.edu/ProblemSolvers/hlawn.html online.

The Pennsylvania IPM program is a collaboration between the Penn State and the Pennsylvania Department of Agriculture aimed at promoting integrated pest management in both agricultural and urban settings. For information, contact the program at (814) 865-2839 or visit http://www.paipm.org online. To view archived news releases, visit http://paipm.cas.psu.edu/newsrelease.html online.

Last Updated March 19, 2009