Monday, June 28, 2010

Hollyhock Weevils (Apion longirostre) are Bad!

Adult hollyhock weevils are often neglected until they start to cause major damage to your hollyhocks. The adults eat tiny holes in the leaves. These holes can coalesce into larger holes as the leaf expands creating an unsightly plant.

The adults are no more than 1/8th inch in length and consequently seldom seen except by those who get their noses within an inch or so of the plant. . Even then the adults may not be seen as these tiny beetles notice changes in light and movement and either hide under the leaves or drop to the ground. This pest is easy to identify as it has an exceptionally long snout as you can see in the photo.

If your hollyhocks have holes in their leaves, the problem is the Hollyhock Weevil. Hand picking this pest off the plant is next to impossible as the adults drop to the ground when the plant is disturbed. You can take advantage of this by placing a sheet under the plant and shaking the stalk. The adults will drop onto the sheet making them easier to capture and crush. Picking off the developing seed heads removes the source of the adults as the larvae feed and develop in the seeds.

A product containing the active ingredient imidacloprid and applied as a soil drench will kill the adults and larval stages. A spray of a product such as permethrin or carbaryl is also very effective. The organic insecticide pyrethrum will also work. Sprays should be avoided in the heat of the day as leaf burn can occur. We have had problems with Pyrethrum burning leaves even when it is sprayed in the evening so treat a small portion of the plant and wait a day to see if any phytotoxicity occurs. Make your additional applications based on the result of your test treatment. Always check the label to ensure the product can be used on ornamental or flowers.

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