Tree Diseases: Gall
Galls are abnormal growths on plants caused by fungi, nematodes, mites, insects and bacteria. Crown gall is the most common of these, attacking a wide variety of plants at the roots and stem, even attacking cane plants such as raspberries and blackberries. There are hundreds of different types of gall disease, according to the University of Delaware, and each is specific to the organism producing it.
Galls are abnormal growth at the stem or roots of a plant, growing like a lesion into a large bump. Fresh wounds on a plant are the most likely areas of infection. Gulls are usually light tan in color, then turn brown to black as they age, says the University of Illinois. If the gall is serious, the plant may become stunted, lose color and die back.
Insects cause gall by the laying of eggs on the host plant. The host plant will react to the laying of eggs by forming the galls at the point where the plant is injured by the egg laying. Control of gall requires prevention, as once the eggs are laid, they are protected by the surrounding gall.
Control is usually performed through the digging up and removal of infected plants and leaving the soil fallow for several years or planting a different, resistant plant variety in its place. Grass grown in the soil that contained the infected plant will usually sterilize the soil within a few years.
Prevention of gall infection requires the sealing of any tree wounds immediately. Grafting of tree and other plants should be done with sterilized tools rubbed with a 20 percent commercial bleach solution or a 1/2 percent solution of potassium pomegranate to prevent the spreading of bacteria.
Preventative measures for gall-causing insects is slightly different. A protective spray treatment of insecticide oil early in the growing season prevents the landing and breeding of gall insects. Although insecticidal oil will not completely prevent pests, says the University of Delaware, it will prevent most egg laying.