We received several calls at the Plant and Insect Diagnostic Clinic with the same question, given the warm temperatures last weekend, can I still prune oaks?
Oak wilt is caused by the fungus Bretziella fagacearum (previously Ceratocystis fagacearum) and transmitted sap and bark beetles. Like many other insects, these beetles' emergence is closely related to temperature (degree day accumulated values).
Sustained warm temperatures do indeed affect the emergence of the oak wilt insect vector, potentially shortening the window to prune oak trees. However, following last weekend's taste of spring weather, the temperature has dropped and been consistently low for this week.
Are beetles active now? According to Dr. Donald Lewis, ISU Department of Entomology professor,” there is usually no insect activity below 55 degrees, so no movement today. Maybe next week….”
Can I prune my oaks this weekend or next week? The low risk of oak wilt transmission in Iowa is from November 1st to April 14th. However, be on the look for warm spells that might increase the risk of transmission.
Should I apply paint to fresh oak pruning cuts? According to Dr. Tivon Feeley, Iowa DNR, "treat the wounds immediately with a wound dressing such as latex and acrylic paint."
The latest US forest service resource recommends treating fresh wounds with paint or wound dressing as soon as possible is pruning while beetle activity is predicted. "Sap-feeding beetles (nitidulids) can find wounds within 10 minutes. Insect vector activity can be predicted by models the Wisconsin DNR one. Avoid moving logs or firewood from stands with confirmed oak wilt to disease-free areas."
For more information, see the US forest service resource page Oak Wilt in the Northeastern and Midwestern States, Iowa Department of Natural Resources Oak wilt page, plus these Iowa State resources Oak Wilt, Vascular Wilts Testing.
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