Western Oak Looper

Asked August 20, 2019, 2:26 PM EDT

We've lived on our Perrydale farm for 28 years. The past five, we've had major western oak looper problems on all our oak groves. We've used Bt spray in the past; it's somewhat effective. Timing is crucial. Right now, the worms have pretty much defoliated our beautiful oak groves. Yet, they are still actively climbing the trunks. I want a spray that I can kill them on contact. Most of the sprays state the worms must ingest the sprayed leaf. There are no leaves left. What do you suggest? Any information would be helpful. I have the PNW Insect Management Handbook, but it's dated. What is the latest research? These worms used to come through the area on 20 year cycles. Not any more ...

Polk County Oregon insect issues

1 Response

Hello, that is interesting. We've seen oak looper south of Corvallis apparently persisting in oregon ash too.

For pesticides you may want to contact a professional applicator and get suggestions. We typically refer to the insect pest guidebook and list of possible chemicals for landscape plants:

Many of these are restricted use, so a professional is important.

All that said, I'm not sure pesticides are the answer. The defoliation is done and we think that natural parasites and predators should be taking their toll on the insects. Pesticide use can eliminate the beneficial insects.

There is little research to back up any of this however, just observations over the years. I'm not aware of any recent research on the western oak looper.

I'd be interested in visiting your defoliated woodland, as this sounds unusual. Perhaps with the State ODF forest entomologist.

We have seen a number of leaf miners and leaf rollers hitting oak this year, especially early in the season, but if there are caterpillars over everything now, that sounds definitely like oak looper.

Email if you like: dave.shaw@oregonstate.edu