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Plant Pathology Infobytes

April 15, 1999

Disease Control Tip for Azalea Leaf Gall

Rainy, cooler weather over the state has been ideal for infection of azalea plants by the leaf gall fungus. Leaf gall, which shows up not too long following bloom, has a way of increasing in severity from season-to-season. This disease is not only unsightly, but reduces the ability of azaleas to produce flowers in future seasons.

What does leaf gall look like? Infected leaves become fleshy and severely distorted. As the galls form, affected parts may become whitish or light green. Sometimes a fleshy rosette of leaves appears at the tip of a branch, or a gall becomes bladder-like as it decays and dries out.

Azaleas are most susceptible to infection by the leaf gall fungus when young leaves appear following bloom. At this time, fungus spores land on young leaves and stems, germinate, and infect these plant parts during rainy weather. Infection cycles occur as long as young leaves are present on plants.

What should home landscapers do about this problem? The best control measure is to remove the galls when they are first noticed. Gall removal helps in disease control, since if not removed, these structures remain on plants or fall beneath plants and are sources of disease spores the next season. In this way, a few galls can spell a lot of future disease problems. Note: Galls should be destroyed and not discarded in the vicinity of the azalea planting.

Gall removal is a fairly routine procedure when only a few galls are present on plants, but there may be situations when galls are so numerous that removal is not practical. In such cases, a fungicide spray program is advisable for disease control.

Here's the procedure for using a fungicide azalea leaf gall control. The best time to spray is once before the new leaves unfurl with captan or a fungicide containing Bayleton. However, if your plants have passed this stage of development, good control may still be obtained with use of either of these fungicides if applications are not delayed too much longer into the season. Apply either fungicide 10 to 14-day intervals during the spring as long as young leaves are present.

Another procedure for controlling azalea leaf gall on badly diseased plants is to cut plants back to a recommended height (check with the County Extension Office for pruning tips). This is a good sanitation procedure and is a good way to reduce disease the following season because galls will be removed along with the pruned branches. It's also advisable to replace mulch beneath such plants since this will insure that fallen galls beneath plants will be removed. Replace with fresh, disease-free mulch such as pine needles or a similar material.

If you need further information about azalea diseases, please feel free to drop by your county Extension office.

Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.