japanese beetle prevention

Asked August 23, 2019, 12:06 PM EDT

I have a horrible japanese beetle problem. I cannot have another season of them destroying hollyhocks, roses, and wisteria. I want to put down milky spore, but I fear it may harm the fireflies that are now in the ground. Is my fear unfounded? If this treatment will harm fireflies, what else can I do?

Howard County Maryland

1 Response

We do not recommend milky spore, because it did not prove effective in recent research. (It should not harm fireflies anyway.)

You should have more success with a product like Grub-Ex.
However, we are surprised you have such a big Japanese beetle problem. Your area, in general, has little to no Japanese beetles this year.

Be sure you are not irrigating in August-September, which encourages the laying of grub eggs and their survival. Also, do not use beetle traps nearby. They attract everyone's Japanese beetles to your property.

It has been found that, since Japanese beetles send our pheromone scents to others when they find a good place to feed, if you kill the first arrivals, you can stop them from attracting the hordes. Knocking them into a container of soapy water held under a leaf works great.

Here is our page on Japanese beetles: https://extension.umd.edu/hgic/topics/japanese-beetles

Ellen