What is a good specific fungicide for grape leaf blight
At the early stage of the disease, spray 50% Xiaojunling soluble powder at 1500 times dilution, or 1:0.7:200 Bordeaux mixture, or 50% carbendazim wettable powder at 700 times dilution; when the disease is severe, spray once equal-amount 200 times Bordeaux mixture, or 500 times 50% carbendazim, or 600-800 times chlorothalonil, once every 10-15 days. After autumn, thoroughly clean the orchard, burn or deeply bury fallen leaves, and spray 3-5 degree lime sulfur mixture before bud break.
I. Introduction to grape leaf blight
Grape leaf blight is also called spot disease, brown spot disease, leaf spot disease, angular leaf spot disease, etc. There are two types, large brown spot and small brown spot, which mainly damage the middle and lower leaves. Large brown spot disease has lesions 3-10 mm in diameter, while small brown spot disease has lesions 2-3 mm in diameter. It generally first appears in May and early June, with the peak period from July to September, and the disease is more severe in rainy years. When the disease is severe, it can cause leaves to fall 1-2 months early, seriously affecting tree vigor and the next year's fruit set.
II. Symptoms of grape leaf blight
1. Large brown spot disease is caused by infection with Pseudocercospora vitis. At the early stage of infection, the spots are light brown, irregular angular spots that gradually expand, reaching up to 1 cm in diameter, changing from light brown to brown and then to reddish brown, with a yellow-green halo around the edge. In severe cases, several spots unite into large spots with clear edges, while the margins on the leaf underside are blurred. Later, the diseased parts die, and in rainy or high-humidity conditions, gray-brown moldy growth appears. Some varieties have lesions with indistinct concentric rings.
2. Small brown spot disease is caused by parasitism of Cercospora brachypus. At the infection point, yellow-green small round spots appear, gradually expanding into round lesions 2-3 mm in size. The lesion area gradually dies and turns brown and then tea-brown, and later black mold layers grow on the lesions on the leaf underside.