Friday, May 11, 2012

Sample of the Week: Oak Leaf Blister

This week, we received two different samples of oak leaves that had the same symptoms. Chuck Hodges, our resident tree disease expert, diagnosed the pale green spots as leaf blister, caused by the fungus Taphrina caerulescens. Disease develops when leaves emerge during cool wet weather each spring. Early symptoms appear as pale yellow to white, irregular spots on the leaves. 
Early symptoms on Southern red oak (Photo: PDIC Database)
Early symptoms on water oak (Photo: PDIC Database)
As disease progresses, infected foliage puckers out, giving the leaves a “blistered” appearance. In late summer, the blistered tissue will turn brown and die. The severity of the disease will vary from year to year depending on early spring weather. Leaf blister affects only the leaves and does not damage the overall health of the tree. Chemical control is neither necessary nor practical on trees in the landscape. However, it may help to rake up and remove fallen leaves. In the nursery, a single application of chlorothalonil, maneb or mancozeb in early spring, just before the buds begin to swell, should be effective. Fungicides applied after bud break are not effective.
Late symptoms on white oak (Photo: PDIC Database)
Special thanks to Chuck Hodges for helping with this post.