Symptom Identification and Key Control Techniques for Early Blight of Tomato

During tomato cultivation, many factors can cause tomato diseases to attack, and among them, tomato early blight is a relatively serious disease. Tomato early blight is also called “target spot”, occurs commonly everywhere, and is one of the important diseases harming tomatoes. For a long time, in some areas, because tomato varieties resistant to viral diseases but not resistant to early blight were promoted, early blight occurred severely. Let us take a look below at the symptoms of tomato early blight and an introduction to the key control techniques.

I. Symptoms of tomato early blight

Tomato early blight, also called target spot, is one of the important diseases of tomato. It is widely distributed, and when the disease is severe, it often causes defoliation, fruit drop, and broken branches, greatly affecting yield, generally reducing yield by 10%—30%, and in some areas reducing yield by as much as about 50%. Tomato early blight can occur from the seedling stage to the mature stage and can attack leaves, stems, and fruits. In the early stage of leaf damage, dark brown or black round or oval small spots appear, gradually expanding to a diameter of 1—2 cm. The edges of the lesions are dark brown, the centers are grayish brown, and they have concentric rings. When humidity is high, black mold layers form on the lesions. Finally, the diseased leaves turn yellow-brown and fall off. The disease spreads gradually from the lower leaves of the plant upward. When the disease is severe, the lower leaves of diseased plants completely wither and die, and it may even cause the whole plant to defoliate. When the base is damaged, grayish brown, oval, slightly sunken lesions often appear at the branching points, and they also have concentric rings. In the later stage, the diseased parts of the stems are often covered with dark brown lesions, and when the disease is severe, it can cause broken branches. Lesions on fruits mostly occur near the stem end in cracked areas. The lesions are round or nearly round, brown or dark brown, slightly sunken, and also have concentric rings. When humidity is high, black mold layers also form on the lesions. Diseased fruits often fall off early. Brown lesions can also appear on fruit stalks and calyxes.

II. Key control techniques for tomato early blight

1. In addition to seed disinfection and raising seedlings in sterile fungus-free soil, strengthen scientific management, maintain rational close planting, and prevent excessive density to facilitate ventilation and light penetration.

2. Strictly control the temperature and humidity inside the greenhouse. Generally, a greenhouse temperature of 18-20°C and relative humidity controlled at 60-70% are suitable. At the early stage after planting, control water for cultivation; water appropriately before flowering; after the second cluster of fruits forms, water thoroughly in time to promote fruit development and enlargement. Watering should be done after 10 a.m. on sunny days, and ventilation should be carried out in time to avoid dew forming on the leaves in the morning.

3. During the growth process of greenhouse-cultivated tomatoes, carry out timely intertillage and earthing up and insert stakes to prevent lodging, promptly remove old leaves and diseased leaves, and take them outside the greenhouse for deep burial. In the middle and late stages, apply potassium sulfate compound fertilizer or water-soluble fertilizer by flushing or topdressing in time to increase disease resistance and raise the sugar content of the fruit. After fruit set, in combination with disease control, spray 0.2% potassium dihydrogen phosphate or amino acid potassium calcium on the leaves.

4. From the seedling stage, first use hymexazol plus agricultural streptomycin; after planting, a 500-fold dilution of 70% mancozeb can be selected for spraying. When lesions first appear, select agents such as chlorothalonil, iprodione, or copper ammonium complex for control.