Leaf blight on azalea plant - Knowledgebase Question

Bethesda, OH
Avatar for geolou
Question by geolou
December 7, 1998
Our azalea plant has a brown coating on its leaves. The plant is located on the east side of the house, surrounded by rhododendrons and geraniums and coneflowers. The blight appeared in late summer and gradually covered the entire plant. What could this be and how may we best combat it?

Answer from NGA
December 7, 1998
It's impossible to diagnose plant disease problems without seeing them, but I suspect that the problem is caused by a rust fungi. These generally attack in late summer, when temperatures range between 55-75F, and heavy dew is the norm. To be absolutely sure, I suggest that you send a sample to your local agricultural extension office (ph# 614/695-5614) or have a knowlegeable nursery person help you identify the problem.

If it does turn out to be rust, here's what you can do. Since the shrub is surrounded by other plants, the leaves probably stay moist for long periods. If the leaf surfaces are allowed to dry, the spores are less likely to infect them. Next spring, either move the shrub or at least create more "breathing room" for it, so leaves can dry more easily.

For now, remove all fallen leaves, which host next year's infectious spores, and burn or bury them. Treat the shrub with care next spring, and take care to water and fertilize only moderately. Excess fertilizer spurs unbalanced growth that invites disease. If you can't move the shrub or make room around it, then you'll need to treat it with a wettable sulfur fungicide every 10 days July-August. Follow label instructions carefully, since sulfur used improperly can cause more harm than good. Best of luck to you!

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