MSU Extension Turf

I received this email question about alternative grub control insecticides. I thought others may have the same question. You can find my answer below.

Dear David Smitley,

We have had questions from our customers at our garden center here in Petoskey about the Milky Spore granular product by St. Gabriel Laboratories and I am having a hard time getting the facts. Have there been any studies done on its effectiveness? Is the grub population here in northern Michigan likely to be other than from the Japanese beetle?

Our customers are looking for alternatives to the chemical options (especially with the publicity concerning honeybees) and I am hoping to help them find some.

Thanks,

Michael Willson
Willson's Garden Center
Petoskey, MI 49770

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Dear Michael,

Unfortunately, the Milky Spore product you asked about did not provide any grub control in the first year of a test we are conducting at Old Channel Trail Golf Course near Ludington, Mich. We plan to continue this test for two more years. Our results so far agree with the results of a test conducted a number of years ago in Kentucky by C.T. Redmond and D.A. Potter. According to Cornell University, the milky spore organism, Paenibacillus popilliae, was the focus of a huge Japanese beetle biocontrol program 60 to 70 years ago, with over 100 tons of spore powder distributed throughout Pennsylvania, Ohio and surrounding states where Japanese beetle occurred at the time. It was considered to be a successful effort because populations of Japanese beetle decreased 10-fold or more at most sites within five years of when the spore powder was distributed.

However, that is ancient history now, and there are three reasons why the Milky Spore product which can be purchased at garden centers may not be appropriate for a home lawn treatment:

1. The bacterium in this product will only infect Japanese beetles and not any other species of grubs, while the most damaging grub to Michigan lawns is the European chafer.
2. The milky spore pathogen may not be as virulent to Japanese grubs now as it was in the 1940s during the USDA biocontrol program.
3. There are no scientific studies conducted at any university that I know of where the Milky Spore product that is now available provided adequate grub control.

Although Japanese beetles have been found near you in Petoskey, it is more likely that people in your area will have June beetle grubs or European chafer grubs. However, Japanese beetles could become common in Petoskey over the next 10 years.

Before discussing alternative management strategies for grubs, it is important to understand that if grubs and turf damage are discovered in April, the only insecticides that will be effective in April are carbaryl (Sevin) and trichlorfon (Dylox). These products do not work as well (maybe 50 percent control) as standard products applied in spring or summer to prevent grub damage the next fall and spring. For more detailed information, on this go to the Michigan State University Turf website and see the grub control bulletin posted there.

Alternative strategies

The standard, and highly effective, grub control insecticides are products that contain imidacloprid, clothianidin or thiomethoxam. There is one insecticide product in a different chemical class that will give a similar level of grub control: chlorantraniliprole (Acelepryn). Apply chlorantraniliprole early (in April or May) for summer and fall grub control.  Chlorantraniliprole applied in April will not work on spring grubs that are already present when it is applied.

Unfortunately, there are not any biological control products that you can purchase at the garden center that will give the same level of control as the standard insecticide products. Some people may want to consider a one-time treatment with a nematode that infects grubs: Heterorhabditis bacteriophora. If you order or purchase a live nematode product for grubs, make sure you buy a Heterorhabditis nematode and not a Steinernema or another type of nematode. Look on the Internet for ‘Heteromask,’ ‘Nemasys G’ or Buglogical Control Systems. The first two are Heterorhabditis nematode products and the third a business that sells Heterorhabditis nematodes.

It is best to apply the nematodes when grubs are present and when the soil temperature is above 50 degrees Fahrenheit. Make sure they are alive when you when get them. You can do this by putting a pinch of nematodes in a glass of water at room temperature for 10 minutes and check to see if they are wiggling. Also, irrigate your lawn immediately before and after applying the nematodes so as many as possible will make it into the soil. The nematodes may not kill as many grubs as the standard insecticide products, but they persist a long time and may even infect grubs for several years after they are applied.

Best strategy is to improve your turf’s health

The best alternative strategy to avoid grub damage is to improve your turf management practices to establish a dense root system in your lawn. Lawns with a large, dense root system are much less likely to be damaged by grubs, and it is much more difficult for skunks and raccoons to dig and turn-over turf with a healthy root system. You can do this by following Michigan State University Extension’s recommendations of setting your lawn mower at the highest clipping height (3-4 inches); applying at least 2.5 pounds of actual N per 1,000 square feet of lawn per year using a slow-release fertilizer several times each year; watering during dry periods; and returning grass clippings and chopped leaves to the lawn instead of collecting and removing them. Visit the Gardening in Michigan website to find a series of Smart Gardening bulletins that include one on fertilizer basics and mowing high for grub and weed control.

If customers ask about the safety of standard neonicotinoid grub control products (imidacloprid, clothianidin and thiomethoxam) for honey bees and pollinators, you can tell them that if the lawn is mowed before the insecticide is applied that it will be safe for honey bees because no open flowers (flowering weeds) will be present when the lawn is treated.

References

Redmond, C.T. and D.A. Potter. 1995. Lack of efficacy of in-vivo and putatively in-vitro produced Paenibacillus popilliae against field populations of Japanese beetle (Coleoptera: Scarabaeidae) grubs in Kentucky. J. Econ. Entomol. 88: 846-854.