Plant Pathology Infobytes
May 17, 1996
Landscape Disease Frequently Asked Questions
Q. The leaves on my oak trees have quite a few circular raised areas which just started showing up in the past few weeks. Is this something that will get worse and hurt my trees?
A. The problem you're describing is oak leaf blister. This is a fungus disease, and while it causes the leaves to grow abnormally, oak leaf blister isn't going to kill the tree, nor will the disease get any worse for the rest of the year. It's too late to carry out control measures at this point in the year, but homeowners who are interested in a program for next year can check with the county Extension office for further information.
Q. Patches of crusty greenish-gray growth are present on the bark of my azaleas, camellias, and some of my plum and apple trees. Can you identify this growth?
A. Sounds like you have lichens on your plants. Lichens are unique creatures in the plant world, since these patches are actually composed on two organisms (an algae and fungus) living in associa- tion with one another. The appearance, however, is that of a single plant. Homeowners often become concerned when lichens showup on plants and think they're causing damage. Not so! Lichens most often appear on plants that for some reason are in a poor or declining condition. Why lichens pick-out weak plants as colonization sites isn't fully understood, but for whatever reason, such plants support lichen growth and it's easy to understand why home landscapers think these harmless organisms are responsible for poor plant growth.
Q. Yesterday, I noticed that many leaves on my azaleas have become thickened and formed whitish, fleshy gall-like growths. These galls detract from the beauty of my azalea planting. What causes these galls, and what can I do about it?
A. These growths result from infection by the fungus which causes a disease know as azalea leaf gall. The best control measure is to remove the galls when they're first noticed. This can be done easily when there are only a few galls present. If the galls are not removed from plants, chances are the disease will become more severe from one year to the next. The galls should be destroyed and not discarded in the vicinity of the plants. There may be situations where gall removal is not practical. In such cases a fungicide spray program is advisable for the control of this disease. Check with us at your county Extension office for further information on recommended fungicides and a program of application.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.