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Treatment Methods for Japanese Beetle Grubs

White grubs feed on the roots of grasses.
White grubs feed on the roots of grasses. David Shetlar, Ohio State University.

 

Japanese Beetle damage in turf. M.G. Klein, USDA Agricultural Research Service, Bugwood.org
Japanese Beetle turf damage. M.G. Klein, USDA Agricultural Research Service, Bugwood.org

 

Melissa Schreiner, Colorado State University, Bugwood.org
Japanese beetle on flower. Melissa Schreiner, Colorado State University, Bugwood.org

 

 

Japanese Beetles are most vulnerable during the grub stage of their lifecycle because they are not mobile and can be found in similar types of environments. Generally, adult Japanese Beetles prefer to lay their eggs in moist turf grass. Moisture is a key component for sustaining a grub in its early stages of development. Adult beetles can be found feeding on over 300 different types of plants and can fly up to 5 miles in their lifetime, so targeting the grubs in lawns is most effective. 

Mesa County recommends treating with Scotts GrubEx. It is a granular treatment spread on turf grass and the active ingredient, Chlorantraniliprole, is the same active ingredient being used in the Japanese Beetle eradication program. The EPA has classified it as a ‘reduced risk’ insecticide and is labeled very safe for humans, pets, pollinators, birds, and earthworms. It does not have a Caution label signifying it is very safe. The best time to treat using this product is May and June.

To prepare your lawn for treatment, be sure to mow prior to treatment.  Additionally, this product must be watered in after treatment so it can seep into the soil to be absorbed by the roots of plants. It can control grubs for many months after treatment.  Please, consider treating your turf grass with GrubEx or a similar product to reduce the potential for spread and protect our greenspaces, agriculture, and ornamental plants. 

Another insecticide option for dense grub infestations is Triclorfon. This insecticide is able to move quickly into the soil to effectively eliminate grubs. However, it rapidly degrades in soil, especially the soil in Colorado. Generally, the best time to use this product is when grub damage can be seen in your turf. It is often used for “rescue treatments” applied to lawns in late Summer after all eggs have hatched (July-September). This product must also be watered in after treatment.

For non-insecticide treatments, you may consider a turf dry down. Grubs are extremely susceptible to low moisture content (drying out) in early stages of development. Eggs are laid by adults from June-August. Drying down requires that a strict watering schedule be followed during those months. Turf can be intermittently watered (once a week) should be avoided during this period to help reduce grub survival. Watering ornamental plants more frequently is recommended so long as no water reaches turf grass areas. 

The City of Grand Junction’s Waterwise Lawn Program offers rebates to residents that opt to convert turf grass for more water conscientious landscaping. For more information about this program, as well as more ways to conserve water and reduce habitat for this pest visit the City of Grand Junction’s Waterwise Lawn Program website or call 970-256-4187.

A biocontrol agent such as ‘Milky Spore’ or products with Bacillus thuringiensis are not recommended for eradication as the biocontrol agents depend on the population of Japanese Beetles to continue, therefore, allowing their reproduction to continue. This does not follow proper eradication methodology and is therefore not recommended.