A question about grub control products and honey bees

Protecting honey bees by using alternative grub control controls and smart gardening.

I received this email question about grub control products safe for honey bees. I thought others may have the same question. You can find my answer below.

Dr. Smitley,

Could you provide the names of grub control products that are not considered neonicotinoids? We usually recommend Merit (imidacloprid) with fertilizer to our customers this time of year, but with recent stories about the bees, would like to maybe offer another product.

Mike Thompson
Hillcrest Sod Farms

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Hi Mike,

This is a very good question. Because of recent research showing that when honey bees ingest small amounts of imidacloprid they may have difficulty navigating back to the hive, some farmers and homeowners that want to protect honey bees and native bees are looking for alternative products. First, there is no reason to believe that imidacloprid or another nicotinoid product applied to a lawn will harm honey bees because bees only feed on the nectar and pollen of flowering plants. Turfgrass does not produce nectar or pollen that bees consume. However, some flowering weeds like clover may be visited by bees. In one study conducted in Kentucky, a scientist found no adverse effects on colonies of bumble bees that fed almost exclusively on clover in a lawn treated with imidacloprid. Still, recent research indicates a risk to honey bees feeding on plants treated with imidacloprid.

The prudent approach is to avoid using imidacloprid on flowering plants that may be visited by honey bees and native bees. Although most lawns are not likely to have flowering plants in the summer, some low maintenance sites may have clover with flowers. Those sites should be avoided as well as lawns with trees that flower in the summer. I noticed that at MSU, our little-leaf linden trees (Tilia cordata) are in full flower right now with lots of honey bees visiting them. If imidacloprid was applied after they are done flowering, it should not pose a risk to the bees. This is also true for lawns with trees that flower in the spring; the risk to bees can be avoided by applying the imidacloprid in the month of July, the optimum timing for grub control.

We do not have many options for alternative products. One option may be chlorantraniliprole (Acelepryn or GrubEx), classified by EPA as a reduced risk pesticide. Results of toxicology work with chlorantraniliprole concluded it is a low risk to honey bees. For grub control in turfgrass, chlorantraniliprole should be applied about a month earlier, in May or June. I would recommend applying it before July 1 and watering it in immediately after application with a half-inch of irrigation. Recent research has shown that all of the insecticides used to control grubs in lawns are more consistent when the lawn is irrigated immediately after application.

Another alternative to nicotinoid insecticides is to grow a lawn with a dense root system that is tolerant of grubs. This can be done without the use of any insecticide. If homeowners set their mowers at the highest setting (clips turf at 3 to 4 inches in height), return their grass clippings to the lawn instead of collecting them, chop tree leaves into the lawn instead of raking, fertilize modestly, and water during dry periods, they will build a dense turf resistant to grubs. Tips on how to do this are available in the Michigan State University Extension Smart Gardening tip sheets:  Mow highmulch leaves, and smart watering.

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

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