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Oak leaf blister bad this spring
The Coast Gardener Newspaper and Web Column - April 27, 2002

Recently, I have seen many oak trees with distorted, tumor-like growths on the leaves. This is a common condition called oak leaf blister.

During the springtime many species of oak are subject to this disease. Numerous cases of oak leaf blister occur here on the Coast in early spring on almost all types of oak, except white oak. This fungus attacks the leaves, but it does little damage to other parts of the tree. The fungus over winters in the bud scales on the tree. You can identify the disease by noticing circular, raised areas up to 1/2 inch in diameter on the leaves. These blister-like spots begin yellow and finally turn brown and die. Unless infection is severe, the leaves remain attached to the tree and there is little noticeable damage.

Control of this disease requires a dormant application of a fungicide during early spring before new growth starts. Raking and disposing diseased foliage will also help break the cycle for next year.

With large trees it is not practical to spray, since the fungus will not kill the tree anyway. It should be noted that once diseased foliage is present, fungicides will not "fix" the damage that has been done. Diseased leaves will simply fall naturally.

A fungicide combined with proper plant nutrition and watering practices can encourage new growth. It is important to remember that this new growth must be protected by a cover spray of the proper fungicide or, it too, will become infected. Again, it is impractical to treat large trees anyway.

Thankfully, it looks worse than it actually is. Since the tree's health is not in danger, don't be alarmed by this pesky fungus. Rake up the leaves and avoid using them in the vicinity of susceptible trees.

This is a good time to address another issue that commonly surfaces when talking about fungicides or any pesticide for that matter. Often, gardeners ask, "What's the single best thing to use for my problem?" Unfortunately, there's no simple answer to this question. First, you must correctly identify the problem. Is it a disease? Is it an insect? Okay, I know us gardeners are never to blame, right?

You must then select the proper management techniques to do the job. In many instances, the problem isn't severe enough to warrant pesticide usage. Never just grab something and start spraying. It may not even work in the first place if it isn't targeted to control your specific pest. For example, a fungicide won't work too well when mealy bugs are what's eating up your hibiscus! Always identify the problem, select the right control measure, and carefully work to solve the problem by doing your homework first.

Until next week, happy gardening!

These archived gardening columns were written by Chance McDavid, former Harrison County Extension Agent.