I’m looking for tactics I can use against curculios attacking my Walnut trees (black walnut, English walnut, and heartnut).
The weevil lays eggs into developing nutlets and new growth.
I pick up aborted nutlets and prune off infected foliage to interrupt the life cycle, but they come back due to other infested trees in the area. The only organic defense seems to be a foliar clay application which I haven’t tried, simply because it doesn’t seem practical.
These little critters are so devastating that I wonder how any walnuts are grown organically at a commercial scale.
Would love some advice, it’s hard to find.
Thank you for contacting Toronto Master Gardeners.
As you describe the Curculio is a devastating pest to deal with. The life cycle of the curculio happens over a couple of years and effects both the leaves and the nuts. Looking through the literature the only treatment which is listed is good sanitation around affected trees. From your letter I gather you are already removing the affected leaves and nuts from your garden. Most sites say that there is no other way to combat them. Part of the issue is it is very difficult to directly treat the insects due to the size of the tree and inaccessibility of the branches.
The foliar clay applications you mention require reapplications after rains so are not often used in the spring which would be a key time for the curculio. The literature I have found does not recommend it for your situation.
As you have exhausted all of the obvious tactics I would recommend consulting a certified arborist. You can find one at: https://landscapeontario.com/.
They should know what has been happening in your community and know what routes are open to you for treatment as they are familiar with Ontario laws and restrictions. They will also be able to confirm that the curculio is indeed what you are dealing with. There may be other diseases which may also be in your community that are compounding your problem.