Tomatoes like most other garden pants can have a disease, a fungus or have a virus attack their fruit and literally ruin your crop. Most novice gardeners have no idea as to what to look for in spotting these more common diseases or what measures to take to control or eliminate them all together. Listed are only a few of the more common tomato fruit diseases and how to treat them if your garden does become infected during this summer's growing season.
Sour Rot - water soaked legions which may or may not have a white scum like growth in the cracks of the tomato. Look for this near the stem and end scar. A fungicide to prevent further spreading may be needed. As for controlling it, keep the fruit off the ground if possible, and water only at the base of the plant.
Anthracnose - is very common and usually affects ripe fruit, it symptoms are dark circular sunken spots with the lesions resembling a bulls-eye as it gets bigger. Water on the fruit makes it worse but to control it a fungicide spray and crop rotation is recommended.
Black Mold- is a combination of numerous fungi on the tomato fruit, to identify this fungus, look for lesions near the stem or scar of the tomato. The fruit will have black or brown areas that will extend all the way into the internal tissue of the fruit. Control is done by keeping fruit off the ground, if however possible, and by limiting wetting by watering at the base of the plant. The use of a fungicide spray may be needed.
Alternaria Cankers- This is a disease that attacks when the fruit is "green" and continues into the ripening period. This is a fungus that over-winters in the soil and can be spread by winds or damage when or if the plant has been pruned. Look for sunken gray lesions to be apparent on the fruit. Control this by the use of a good fungicide spray and again water at the base line of the plant.
Cottony Leak- This will definitely cause fruit rot to your tomatoes, look for large water soaked areas on the fruit that have off color light and dark patches. The fruit will look fine until touched then a watery spill of the internal fruit will flow out. Control this by watering only the leaves and keeping the fruit off the ground and you may require a fungicide spray.
Cloudy Spot- Generally cause by "Stink Bugs" from weeds, their feeding on the fruit will cause the tomato fruit to have white or yellow flecks in the tissue right beneath the skin. If you peel the fruit at the affected area you will see a hard whit cork like tissue. Since when the bugs are feeding it is not noticeable, a good insecticidal preventive spraying will help to control them.
Spotted Wilt- Yellowing older leaves with large yellow, red and green lesions on the fruit and the malformation of the fruit caused by this virus will need special attention. This virus stunts the plant. Onion thrips from ornamental flowers and shrubs that play host to the virus carry it from one infected plant flower to another. Generally elimination of the plants that carry this virus is best. Clean cultivation is highly recommended.
Blossom End Rot- Affects fruit at all stages of its development and be wary of secondary infections. Look for symptoms such as sunken black leathery spots on the fruit and a deterioration of the fruit at the blossom end. Generally cause by a calcium deficiency in the soil and water stress from not watering at the base line or over-watering of the plant itself. Control this wit fertilization of lime and calcium before planting and remember to irrigate and mulch properly.