Q&A: How do I get rid of Japanese beetle grubs?
Q: What can I do right now to get rid of Japanese beetle grubs so they won’t attack my plants this summer?
— Paul from Youngstown
A: It is quite early to be thinking of these insects in the adult form, but the grub is indeed alive and well in the soil. Your best plan of attack should be preparation.
Controlling Japanese beetle grubs in your lawn will NOT control populations because the adults fly around all over the neighborhood. While controlling these grubs in the lawn will reduce the grubs’ feeding on the roots of your lawn (if it is that bad), it will not control the thousands of other grubs in neighboring lawns. Those grubs will become the adults that still affect the plants in your landscape even if you try to control yours this spring.
Japanese beetles have a tremendous sense of smell. They can travel miles to aggregate at their site of their favorite foods. They use pheromones (a scent used for communicating) to tell each other where the good eats are located.
So when they emerge as adults this summer, plan to get the first beetles (the scouts) and eliminate them before they can tell the other beetles where your good tasting plants are located. You can do this by drowning them in a cup of soapy water. Don’t squash them.
To do this effectively, you need to know when they will arrive in your yard. Most years, we’ll see the first Japanese Beetles just after the fourth of July. But, this changes year to year based on growing degree days — a measure of our overall warmth of the season. You can put your zip code into this site around that time to see if the beetles are close to emergence: http://go.osu.edu/growingdegrees.
This year’s population is linked to the amount of moisture available for eggs just after the eggs are laid and while the first instar larvae are developing. If it is dry and if you avoid watering during this time, the population will be low next year.
For landscape plants, your best bet is to scout for the first adult beetles. Remember, they are only active for a couple of weeks. They can do a lot of damage in this limited amount of time, though, if you do not control these first “scout” adult beetles.
And the traps are a waste of time and money. You are simply attracting more beetles to your yard and do more harm than good.
Know the life cycle for Japanese Beetles by visiting http://go.osu.edu/JapaneseBeetle.
Barrett is The Ohio State University Extension educator for agriculture and natural resources in Mahoning County. Call 330-533-5538 to submit your questions to the plant clinic. Live clinic hours are 10 a.m. to noon Mondays and Thursdays. Or visit go.osu.edu/mahoningclinic.