New Ways to Combat Japanese Beetles

The Left Hand Valley Courier has some talented readers, among them some knowledgeable gardeners. Reader Katy Bohn, whose garden was featured in the LHVC last summer, is also a member of the Boulder Valley Rose Society (BVRS), the group in charge of the Boulder Dushanbe Tea House rose garden. She and her fellow BVRS members all have home gardens that were also ravaged by the increased number of Japanese Beetles (JB) this past summer, and they were busy trying to protect the rose bushes at the Tea House with whatever natural methods they could use. The members of the BVRS have spent the past four years educating themselves about this plague of tiny pests.

Bohn offered up her understanding of what is proving to be most effective in the control of the Japanese Beetle problem.

“We feel the most reliable source is the CSU extension,” Bohn wrote via email, “and a good article written by Dr. Whitney Cranshaw about the JB.”

Dr. Cranshaw is a professor of entomology and is responsible for developing pest management programs for the state of Colorado. He has done extensive work developing JB control methods, and a link to his article sharing these methods is at the end of this article.

Cranshaw notes that the use of Milky Spores, an organic method used in JB control, takes several years’ application to work and even then, is less than 5% effective. Nematodes, another suggested method, are effective for attacking the grubs, but the application methods matter.

Bohn wrote, “It is important to note that short exposure to a day that is above 90 degrees or below 55 degrees will kill your nematodes. The best time to apply them is late summer or early fall--not late fall--when the grubs are small and the temperature is right.” Nematodes can be bought at many local nurseries and garden supply stores, or ordered online.

A relatively new product that has not been readily available, but has proven very effective, is Bacillus thuringiensis var. galleriae (Btg).

Btg is a bacterium that must be ingested by the bug. It then acts as a poison, destroying the insects’ midgut and killing them within days. It must be applied every year, and should be applied to your lawn when you see the beetles in your garden. It is considered organic and does not harm bees, birds, aquatics or pets.

Being relatively new and previously marketed for larger agricultural uses, coming by Btg has proven difficult for the average homeowner. Most local garden centers don’t carry it, and finding it through online retailers, such as Amazon, has been difficult. However, now two local garden stores--Harlequin Gardens and Sturtz & Copeland Flowers and Plants--carry it.

Jason Shimmel of Sturtz & Copeland, located at 2851 Valmont in Boulder, offers up some effective, current methods for getting the Btg where it belongs to kill as many beetles as possible each year.

“We’ve learned that mixing the Btg with a liquid fertilizer, such as Neptune’s Garden, in a one-gallon hand pump sprayer and then applying that mixture to your lawn right now, when the beetles have gone underground into your lawn to lay their eggs, is thus far the most effective method.”

Sturtz & Copeland carries a Btg product sold under the brand name “beetleGONE”. Shimmel recommends mixing one ounce of the Btg and three ounces of a liquid fertilizer with one gallon, and then watering the lawn a bit afterward to help the mixture get down to where those grubs are growing.

If you haven’t already been using Btg earlier this year when the JB were still visibly active, then now through mid-October is the time to apply in order to help keep the population under control come springtime.

Many of the nursery staff at Sturtz & Copeland have been educated in the use of Btg, and are happy to provide whatever guidance available to help Boulder County residents rid their gardens of these incredibly invasive, non-native and destructive pests. It has proven to be an ever-growing problem that cannot be controlled organically and safely until we all work together.