Oak Leaf Blister: To Treat or Not to Treat?
May 19, 2014
Keeping your trees properly pruned, watered and healthy is the best way to avoid pests and diseases. But we're still suffering from drought in our area and trees are showing stress. Right now, we are seeing oak leaf blister, a fungal leaf spot disease caused by the fungus that affects all species of oak trees. If your trees are healthy and vigorous, this fungal disease will generally not be a major concern. Trees that are weakened from drought or poor maintenance can be greatly affected and suffer early defoliation and reduced vigor.
In early spring, you’ll begin to see small rough spots on leaves. As foliage grows, the spots will turn brown and tough. As leaves become damaged, they’ll begin to fall. If the tree is well established and experiences a heavy defoliation before mid-summer, it may push out new leaves in late summer or fall. If the defoliation happens in late summer or early fall, then impact on the tree's vigor could be reduced as it heads into winter.
We don't always recommend treating for oak leaf blister. Once infection occurs, treatments are often ineffective. Proper pruning and removal of leaves will help contain the fungus. Keeping trees properly fed, watered and maintained will keep many fungal diseases at bay. However, if you have young trees that have been previously infected, they should be treated with a protective fungicide when buds begin to swell in early spring.