High temperature and frequent rain during the walnut yield formation period: how to prevent and control anthracnose

    Mid-to-late August to early September is the main period when the walnut yield is formed, and this period coincides with high temperature, frequent rain and humid air, when many diseases occur at high rates, seriously affecting walnut production. During this period, the main walnut disease is walnut anthracnose, while other diseases mostly occur only mildly.

Walnut anthracnose

    Walnut anthracnose

    Disease symptoms: after the walnut is affected, brown to dark brown round or nearly round lesions grow on the husk, with a sunken center and small black dots, and some appear in concentric rings. When air humidity is high, raised pink lesions appear on the spots. When there are many lesions, they can merge into patches, causing the walnuts to turn black and rot or drop early. Leaf lesions are irregular in shape, mostly strip-like. The leaf color at the lesions turns withered yellow, and severely diseased leaves turn entirely yellow.

    Conditions for disease occurrence: the disease occurs from June to August, and is severe in walnut orchards with high rainfall, weak tree vigor, dense branches and leaves, and extensive management; the pathogen spores invade through wounds or natural openings of the walnut fruit.

    Control methods: (1) Remove diseased branches and collect and burn diseased fruits and leaves. Strengthen tree management, and improve ventilation and light penetration. (2) When the rainy season comes, spray Bordeaux mixture at 1:1:200 (copper sulfate: lime: water) once every 10-15 days to prevent walnut anthracnose. (3) When the disease occurs, spray 40% thiram wettable powder at 800 times dilution, or 50% carbendazim wettable powder at 1000 times dilution, 75% chlorothalonil at 600 times dilution, 70% thiophanate at 800 times dilution, once every 15 days, for 2-3 consecutive sprays.