Tuesday, July 26, 2022

Residents see Japanese beetles after spraying insecticide, entomologists explain why

Crews sprayed insecticide on lawns
in Grandview this past spring, treating
for the recently discovered infestation
of Japanese beetle.
Amber Betts
WSDA Communications

Just a few years ago Grandview residents didn’t have to worry about an invasive pest gobbling up their roses, or making it impossible to have a green and full lawn. Now, Japanese beetles are in full force as they’ve begun to emerge from their winter, underground homes.

Last year in 2021, we saw these non-native Japanese beetles grow exponentially in population. This year, before the ‘adult flight season,’ our eradication teams took to the lawns of Grandview and applied an insecticide to help curb the population of these beetles. So why are we seeing thousands of beetles? Didn’t the treatment work?

What was the point?

These questions may be on the minds of many Grandview area residents as we begin to see a larger population of Japanese beetles than last year.

Since last fall, Japanese beetle grubs have been underground, growing, and preparing to emerge this summer as adults. Our entomologists explain, the treatment that was applied this past spring will not affect the grubs. The active ingredient wasn’t strong enough to kill these ground-dwelling, uninvited guests, because they were too big, almost full grown So, now we’re seeing an even larger population of beetles this year. So why do the treatment at all? What was the point?

The adult beetles that are flying around our yards now, eating a big feast and mating, are laying eggs. These eggs will hatch very soon, and they will begin to eat the roots of the grass. Their regular life cycle says they will continue to grow all winter, and emerge as adults next summer. However, when they eat the roots of a treated lawn, because they are so small, they will not survive.

That’s why we won’t see the results of this year’s treatment until next summer, when the beetle eggs that were laid this summer begin to emerge from the ground and take flight. We anticipate seeing a decline in the population in summer 2023.

However, we can’t do this with treatment alone.

We need your help

Our teams are on the ground daily checking the Japanese beetle traps, more than 2,300, while also working on ways to dispose of our yard waste, and instituting a proposed quarantine that would limit the spread of this pest beyond the current infestation zone.

The quarantine proposal will have a public hearing on August 2. We encourage as many voices to participate as possible, it’ll be held at The Learning Center at 313 Division St. at 10 a.m.

While we are waiting for the final touches to be put on our yard waste disposal site, we are asking residents who want to join the fight against these pests to keep all yard waste like lawn clippings, sod, and others on their property until our site is ready. Crews are working hard to get the disposal site ready. Once it is ready, we will be able to take yard debris and green waste from all businesses and residents inside the infestation area. From there, we will be chipping the items to ensure they do not house a place for beetle larvae to hatch, grow, or reproduce. 

Keep an eye out for more information on that soon.

What else can I do?

Residents who want to do more to help can place traps on their property, reporting their findings, and use WSU’s treatment guide, to treat their properties for the adult beetles.

Be on the lookout for a treatment request from WSDA for next year’s eradication effort, pending funding, in early 2023. We want to get that second round of treatment on as many lawns as we can, to sway the Japanese beetle population from growing into our crops and ultimately affecting our food, and local ag economy. Residents and other interested parties can stay in the loop on all our efforts by joining the Pest Program email listserv. (make sure “Japanese beetle” is checked, or join the Japanese Beetle Watch Facebook group.