Growing Green

By Robin Trott, Extension Educator

White grubs have been causing problems in Minnesota lawns for several seasons. These larvae come from beetles like Japanese beetles, masked chafers and May/June beetles, and they feed on plant roots. Here’s how to recognize and manage a grub infestation.

Identifying Grub Damage

Signs of white grub damage include irregular patches of dead or dying grass that look like drought stress. This damage is evident even after watering or rainfall. Moderate damage shows dead turf with few roots when pulled up. Severe damage often results from animals like raccoons and skunks digging up the lawn to eat the grubs.

Managing Grub Infestations

Finding grubs doesn’t always mean you need to take action. A healthy lawn can handle some grub presence. It’s best to treat the lawn only if there is visible damage or if there was severe damage the previous year. White grubs are most active from May to September, making treatment timing important.

Curative Treatments

For grub damage in late spring or early summer, use a curative insecticide with active ingredients like carbaryl, clothianidin, imidacloprid, thiamethoxam, or trichlorfon. Stop these treatments once the grubs enter the pupae stage, as they stop feeding and treatments become ineffective.

Preventative Treatments

If you had a severe infestation last year or expect one, a preventative treatment is recommended. Products containing chlorantraniliprole (e.g., GrubEx or Acelepryn) are effective and have lower toxicity. Apply these between May and early July. Avoid neonicotinoid insecticides (clothianidin, imidacloprid, thiamethoxam) as they can harm bees and other beneficial insects.

Biological Insecticides

Several biological insecticides target white grubs. Bacillus thuringiensis galleriae (GrubGone) is effective as a preventative treatment. Apply it before an infestation begins. Bacillus popillae (Milky Spore) is not effective against lawn grubs.

Application Tips

Apply any insecticide before a rain or irrigation event with at least half an inch of water. Mow the lawn before applying to remove flowers and reduce the exposure to pollinators. This also helps granular products reach the soil.

By understanding the signs of grub damage and choosing the right treatment, you can keep your lawn healthy and green.

Until next time, happy gardening!

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“I believe a leaf of grass is no less than the journey – work of the stars.” ~ Walt Whitman