Symptom Identification and Control Techniques for Peanut Leaf Spot Disease

(Agricultural Wealth Network) Peanut leaf spot disease is the collective term for peanut black spot, brown spot, net blotch, and scorch spot. It is an important disease of peanuts and has a considerable impact on peanut yield and quality. I. Symptoms Peanut leaf spot disease is mainly caused by black spot and brown spot. Compared with brown spot, black spot occurs more widely and causes more severe damage. Both diseases mainly damage the leaves. When peanuts are affected, symptoms first appear on the lower leaves and then gradually spread to the upper leaves. In the early stage of the disease, small brown spots appear and gradually develop into round or irregular lesions. Brown spot lesions are larger and have a yellow halo around them, while black spot lesions are smaller, darker than those of brown spot, with neat edges and no obvious halo. In humid weather or during prolonged rainy periods, the lesions may merge with one another into irregular large spots, and the leaves become scorched and withered, seriously affecting photosynthesis. If it occurs on petioles, stems, or pegs, mild cases produce oval dark brown or brown lesions, while severe cases cause the entire stem or peg to turn black and die, greatly reducing peanut yield. II. Control Since both diseases are caused by fungi of the subdivision Deuteromycotina, the control methods are basically the same. Control should focus mainly on agricultural measures to eliminate the initial pathogens, and chemical control should be used when necessary. In addition, attention should be paid to selecting disease-resistant varieties. (1) Eliminate the source of the disease. After the peanut harvest, promptly remove the diseased plant residues left in the field, and do not throw them around or pile them up at will. Plots with diseased residues should be plowed in time to accelerate the decomposition of the diseased residues. Before planting peanuts, the peanut vines in the field should be completely disposed of to prevent the pathogens from infecting the peanuts. It is best to rotate peanuts with corn and rice. (2) Select disease-resistant varieties. The more resistant varieties are generally those with upright growth, thick leaves, dark color, and large peanut seeds, or early-maturing varieties. In plots with severe disease incidence, these varieties can be selected for planting. (3) Strengthen cultivation management. Sow at the proper time, plant at a reasonable density, apply sufficient basal fertilizer, and topdress in time to promote robust growth of peanuts and improve disease resistance. (4) Chemical control. Spray pesticides in time at the early stage of the disease to reduce the severity of the disease. Relatively good pesticides: 80% zineb 400-fold solution, 70% thiophanate-methyl 1000-1500-fold solution, 50% carbendazim 1000-1500 solution. When spraying, be careful to spray evenly and thoroughly. If 0.1 kg of soybean powder or washing powder is added to every 50 kg of spray solution, the control effect is better; spray once every 10-15 days, for 2-3 consecutive sprays, which can basically control the occurrence of the disease.