Diseases

Early Blight, a fungal disease, produces dark brown target-like spots on lower leaves, which then turn yellow and drop. Leaf loss exposes fruit to the sun, producing cream-colored, hard patches of sunscald and decreased fruit production. Tomatoes are still edible but the damaged part should be removed. Warm temperatures, abundant rainfall (or irrigation) and high humidity are ideal for the development of early blight.

To manage the disease and decrease the fungal reservoir, remove heavily infected leaves. Avoid overhead irrigation. Splashing water transfers fungal spores from infected to non-infected tissue. Avoid brushing against tomato leaves when they are wet to avoid spreading the disease. In the fall, remove plant debris from the garden as the fungus over winters on it. Next year, locate tomatoes in a different area. Space plants further apart to increase air circulation and improve leaf drying.

Psyllids are aphid-like insects that suck sap from plants. While feeding, they inject toxic saliva that causes a group of symptoms known as psyllid yellows. Leaves turn yellow with purple veins. Stems and leaves become distorted and stunted. A sugary substance produced by the insects is usually found on leaves, stems, fruit and even the soil surface under the plant. In addition to affecting the appearance, psyllid yellows also causes plants to develop large crops of small, flavorless tomatoes. There is no control for the disease other than to control the psyllids before populations damage plants. To control, apply sulfur dust, permethrin, horticultural soap or horticultural oil.

Blossom end rot develops as a dark brown to black, sunken discoloration on the blossom end (bottom) of the fruit. This physiological problem occurs when insufficient calcium is transported to the developing fruit. (Calcium is needed in the proper development of the fruit cell walls.) Irregular watering is the usual culprit, since calcium is taken up by plants only when dissolved in water. Cool soil temperatures can also cause blossom end rot, since they limit root development and nutrient uptake. To correct the problem, water plants consistently and apply mulch to keep soil moisture levels even. Avoid planting tomatoes too early in the season.

Physiological leaf roll causes leaves to roll upward and inward and become leathery and firm. The problem appears on the lower leaves first. Leaf roll is usually due to irregular watering, although heavy applications of nitrogen and excessive pruning have also been implicated. Some varieties are more prone to leaf roll than others. If any discoloration accompanies the leaf rolling symptom, virus or psyllids may be involved. 2,4-D herbicide drift also causes leaf roll symptoms, but leaves are usually rolled downward, elongated and have white veins.