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Sunday - June 08, 2008

From: Helotes, TX
Region: Southwest
Topic: Trees
Title: Best time to trim oak trees to avoid oak wilt
Answered by: Nan Hampton

QUESTION:

When is the best time to trim oak trees? Concerned regarding oak wilt if cut at wrong time. Ball moss is not harmful but will it help or harm if trees trimmed. These are large oak trees. Thank you.

ANSWER:

The Nitidulid beetles that carry the fungus (Ceratocystis fagacearum) that causes oak wilt are most active from February through May. Their activity declines as the summer temperatures rise but they are still around June through October. Their activity also subsides during the colder months November through January. Definitely, do not trim your trees from February through June. Probably the best time to trim is during a particularly cold period in the November through January range. Alternatively, the very hottest months—July, August, September—would be a reasonably safe time to trim. No matter when you trim be sure to paint the wounds IMMEDIATELY with pruning paint or even latex paint.

Read "Guidelines for Proper Pruning to Prevent Oak Wilt Infection" by Kim Camilli (Oak Wilt Coordinator, Texas Forest Service) and "Studies on Pruning Cuts and Wound Dressings for Oak Wilt Control" by Kim Camilli, David N. Appel, and W. Todd Watson. Arboriculture & Urban Forestry 2007. 33(2):132-139. Also, visit the Texas Oak Wilt Information Partnership page for more information.

Regarding the Tillandsia recurvata (small ballmoss), they are epiphytes and not parasites; however, if they become too numerous on the limbs they can shade out leaves where photosynthesis occurs and interfere with the health of the tree. You don't really need to trim off the branches to remove the ball moss unless the limb itself is already dead. You can remove the ball moss from the limbs mechanically. There are also chemical controls, but unless the density is high, you probably can leave them where they are with no harm to the tree.