Do grub control products work?

When to apply grub control products, how reliable they are and why some people are confused about whether they work.

If you see grubs in April – May, the effective time to apply insecticide is late May – August.

If you see grubs in April – May, the effective time to apply insecticide is late May – August.

A residential fertilizer supply company in northern Macomb County recently contacted a Michigan State University Extension regarding questions on grub control products. He wrote, “I have some concerns that the grub preventative treatments I do with Merit don’t seem to be working. I’m not sure if there’s a resistance issue or if the sandy soils aren’t allowing the product to bond to any organic matter. Let me know if you have any recommendations on what type of strategy I should follow this summer.”

My response is below and explains when to apply grub control products, how reliable they are, and why people sometimes have the misconception that they do not always work well.

I am glad you asked this question because many people want to know how reliable insecticide products are for grub control in lawns. We have just compiled our grub research test results from the last 25 years. Imidacloprid (Merit, etc.), clothianidin and thiomethoxam are extremely reliable when applied at the commercial product label rate of 0.4 pounds active ingredient per acre between late May and mid-August. Chlorantraniliprole is nearly as effective.

Applications made after Aug. 15 are not as reliable and do not work well at all after late September. We have only seen a failure in maybe one out of 50 treatments, and that was when we sprayed a grub control product during a hot and dry period and it did not rain for several weeks. Even that can be prevented by applying 0.25 to 0.5 inch of irrigation immediately after application.

Our grub research tests were conducted at several different sites, some of which with very sandy soils. They worked well in all soil types.

Homeowner products direct consumers to apply their products at a lower rate of 0.25 pounds active ingredient per acre. Also, the commercial combination products that contain imidacloprid, clothianidin or thiomethoxam with a synthetic pyrethroid like bifenthrin are labeled at a lower application rate of 0.25 pounds active ingredient per acre. That is a low enough rate that if it is applied too early (April), it may not work as well in August and September when the grubs are there.

The most common reason people think an insecticide failed to work for grub control is because they are looking at grubs in spring (April and May). Our best grub control insecticides (imidacloprid, clothianidin, thiomethoxam and chlorantraniliprole) do not work on grubs in spring.

In spring, grubs are near the end of their one-year life cycle and are not susceptible to insecticides. The insecticides you apply from late May to mid-August work on the next generation of grubs present from August to late October then next spring. With a good preventing insecticide application made from late May to August, you will not see any grubs in fall or next spring.

More information is available in the MSU Extension article, “How to choose and when to apply grub control products for your lawn.”

Dr. Smitley’s work is funded in part by MSU’s AgBioResearch.

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