Symptoms of plant disease include failure to thrive, wilted leaves and failure to produce flowers or fruit. Fungi infections cause most plant diseases. Bacteria, viruses and nematodes are other living organisms, or biotic, reasons for plant disease. Abiotic, or nonliving, reasons for plant disease are environmental, mechanical or improper garden technique.
Root, Crown Rot and Cankers
Root and crown rot related to water molds are also fungi that spread by water in the spore stage. Well-drained planting beds will control this fungus. There are at least six additional fungi that live in the soil and attack the root or crown of plants. They are difficult to treat because they attack the plant's root system where the fungicide doesn't reach. Fungi can cause canker infections in the bark of trees or shrubs. The canker will be a different color than the tree's bark. According to Ohio State University, this fungus spreads its spores through splashing water, insects and wind.
Ohio State University research has shown the family of powdery mildew diseases to be fungi that infect specific hosts, such as roses, sycamore and lilacs. The fungi leave a white growth on the leaves and stems of the plant, and the spores blow to other plants. After the fungi die, leaves that still have the white powder on them will need to be pruned.
Rust is a symptom of a type of fungi that are host specific. Plants will have spores that are orange or red in color and form a mass. The fungi will cause spots or lesions on the leaves, fruit and twigs. Crabapple, hawthorn, snapdragon and hollyhock are examples of some plants rust will attack.
Leaf Spotting and Blight
Leaf spotting and blight can be caused by bacteria such as leaf spot, fireblight or crown gall. They can also be caused by fungi, such as anthracnose or black spot of rose. According to Ohio State University researchers, anthracnose is common and shows up as irregular brown areas on the leaves, generally along the main leaf vein. It will cause early leaf drop, generally in late summer. Where rust and powdery mildew are host specific, leaf spotting and blight are not. They spread by air and splashed water.
Practice Sound Gardening Technique
Practice sound gardening techniques for plant health. Water properly, minimize cultivation damage and space plants correctly. While the weather cannot be controlled, damage it creates can be mitigated. Composted soil allows rainwater to drain through. Mulch around tender plants protects them during cold months. Cover young plants if frost is predicted. Check soil moisture during prolonged heat or wind. Prune injured plants. Weed regularly. If using a chemical fungicide, follow the manufacturer's instructions. Be sure to spray the fungicide on upper and lower leaves and the stem.