Bacteria, fungi and viruses commonly cause disease in Florida gardens, especially during the heat and humidity of summer. Most of the disease-causing organisms are visible only with a microscope, but the presence of these pathogens is indicated by disease symptoms. Not all disease is caused by pathogens--some disorders are caused by the environment and chemical or physical damage.
Damping-off is a seed or seeding disease. Decay of the root or stem occurs before or after emerging from the soil and the seedling stem collapses near the soil surface. Damping off is caused by soil-borne fungi and the result of planting seeds too deep or planting seeds in wet soil.
Southern Blight is found in humid, hot summer weather. Soil-borne fungi affect plants such as tomatoes, peppers, okra and eggplant. After growing slowly, plants turn yellow and die. A thick, spiderweb-like cover is often observed on the infected plant, as well as on the ground around it.
Fungal spot diseases are observed as spots with dark borders on plant leaves. Fungal spots are either round or oval and often have dark or fuzzy centers.
Soil-borne fungi cause fusarium wilt disease (common in Florida) on beans, crucifers (such as cabbage, cauliflower, broccoli), eggplant, okra and tomatoes. Plants infected by wilt disease caused by fungi will yellow and die, and the cut stems will show narrow brown streaks.
Fungal diseases can be controlled by used of a foliar fungicide, but careful attention to the usage label is important. The best methods of reducing fungal disease include removal of decaying plant matter from the garden, elimination of disease-harboring weeds, and watering in the morning so foliage dries rapidly.
Mosaic diseases in the garden are caused by viruses. Tobacco (or tomato) mosaic virus commonly affects tomato plants. Viral diseases spread easily from plant to plant of the same family, so other plants in the vicinity of the infected plant are vulnerable. Mosaic virus symptoms appear on leaves, which feel bumpy and look cupped and have an unusual shape. The best measures for avoiding mosaic diseases include planting disease-resistant varieties of plants and rotating garden crops when planting each season. Control of disease-spreading insects, such as whiteflies and aphids is also important.
Bacterial spots are common on beans, crucifers, peppers and tomatoes. Spots will occur after rain when water carrying bacteria splashes on plant leaves. Bacterial wilt diseases cause plants to appear wilted and affect potato, eggplant, pepper and tomato. Infected plants will die quickly, without first turning yellow. Dispose of severely diseased plants (but not in the compost pile), use clean garden tools, and use disease-resistant plants to guard against disease outbreaks. When in doubt about disease identification, a local county extension office is a recommended source for assistance.