Diagnosis and control of tomato gray leaf spot (brown spot)

Gray leaf spot is also called sesame leaf spot by vegetable farmers in production. It mainly damages the leaves, and in severe cases, the petioles are also damaged. In the early stage of the disease, the leaves are covered with small light brown dots. The lesions are water-soaked and irregular. The middle part of the lesions is gray-brown to yellow-brown. The edges of the lesions are yellow-brown halos. The lesions are sunken and 2 to 5 mm in diameter. , the lesions are prone to perforation in the later stages.

【Atypical Symptoms】 The lesions are reddish-brown round spots. In the early stage of onset, the leaves show small reddish-brown round spots. The center of the lesion is light gray, and the brown halo appears on the side by side. The lesions are slightly larger than the gray leaf spot and the color is brighter. After expansion, the lesions become contiguous brown round spots and the leaves turn yellow. The prevention and treatment of brown spot is the same as that of leaf spot.

【Cause of the disease】The pathogen overwinters in the fields as mycelium and diseased remains. Molecular spores are spread by airflow, irrigation water, and rain splash, and invade through stomata. Warm, humid, rainy weather, dense planting, and windy environments are prone to the disease. Flooding, high humidity, insufficient fertility, weak plant growth and serious disease incidence. Generally, planting in protected areas in spring has a higher incidence of disease than in autumn, and the epidemic speed is faster. Due to the high yield of hard fruit planting bases, sufficient amounts of organic fertilizers and compound fertilizers need to be invested. On the contrary, losses caused by disease epidemics due to fertility and extensive management are inevitable. , should be paid great attention to and prevent early.

【Rescue method】
Ecological control: Reasonable dense planting. The density of introduced varieties is generally smaller than that of domestic varieties, but the yield is higher. Appropriately apply biological fertilizers and phosphorus and potassium fertilizers, strengthen field management, reduce humidity, and enhance ventilation and light transmission. After receiving the goods, promptly remove diseased remains and disinfect the soil.

Chemical control: It is recommended to use the general tomato disease prevention and control prescription for overall prevention. Because it is highly sudden and difficult to prevent, taking 25% Azoxystrobin 1500 times for prevention will have a very good effect.