Pensacola News Journal

For: Saturday, April 24, 2004

By: Daniel E. Mullins

Extension Horticulture Agent

Santa Rosa County

Azalea Leaf Gall Common This Spring, But Not Serious

The incidence of azalea leaf gall is common this spring. Check your azaleas. If you find that the new growth contains thickened, fleshy and distorted leaves, then your landscape is one of many experiencing this disease.

Azalea leaf gall is caused by the fungus Exobasidium vaccinii and only occurs on the first flush of growth during some springs. Infection is favored by cool, moist weather just as new leaves are emerging.

What few showers that the Gulf Coast experienced during March occurred almost exactly when spring growth started and we all know how unseasonable cool the weather was at that time. So the stage was set for azalea leaf gall, and the questions that the Extension office has received about this disease were predictable.

This disease does not seriously threaten the health of azaleas, but there is one practice that can help to reduce the incidence next spring. These thickened leaves or galls should be pulled or clipped from plants and disposed of. If left on the plants they will dry, turn brown and fall to the ground where the fungus carries over until next spring.

Fungicides for controlling azalea leaf gall are of little use at this time of year. By the time that the galls are present, the disease is at the end of its cycle and sprays to control it will have no effect. The application of an approved fungicide before and as the growth buds open and expand in early spring can reduce infection, but the timing must be so precise that this practice is not generally recommended.

The life cycle of this particular disease provides some insight into the fascinating world of plant pathology as well as the plant and disease relationship. The spores of this disease are spread by wind or by splashing rain where they land on newly emerging leaves. Spores germinate and as they grow in the leaf tissue, stimulate it to produce giant cells instead of normal sized ones. The diseased leaf grows four or more times thicker than normal and is very succulent. The color of the upper leaf surface remains nearly normal, while the lower surface cracks and peels back revealing a white spore producing layer.

When left on the plant, galls later turn brown, dry and fall to the ground, where they lie dormant throughout the summer and most of the winter. Now here is the interesting part: The following spring, just as new growth is about to occur, tiny structures begin to grow from the previous year’s infected leaves and release spores into the air at just the right time for infection.

These specialized spore bearing structures go unnoticed because they are so small and are well camouflaged, growing in mulch and leaf litter at the base of azalea plants. They are dark and smaller than a match head, looking like a tiny mushroom.

Question of the Week: Is it too late to establish tomato plants this spring?

Answer: According to our University of Florida Vegetable Gardening Guide the end of April is the latest recommended time for planting tomatoes for summer harvest in North Florida. The problem with later planting is related to high temperatures as the season progresses.

Tomatoes are very sensitive to high temperatures and have difficulty setting fruit when nights are above approximately 74 degrees F. Gardeners who plant as late as May, should consider the so called “Hot Set” varieties such as Solar Set and Heat Wave, or the smaller fruited varieties. These have the ability to set fruit under slightly higher night temperatures.