What are the common late-season fruit diseases of walnut trees?
What diseases affect walnut tree fruit in the late season? The following diseases affect walnut tree fruit in the late season: 1. Walnut anthracnose. Disease symptoms: after the fruit is infected, brown to dark brown round or nearly round lesions appear on the rind, with a sunken center and small black dots, sometimes forming concentric rings. When air humidity is high, the lesions bear...
What diseases affect walnut tree fruit in the late season? Please explain.
The following diseases affect walnut tree fruit in the late season:
1. Walnut anthracnose
Disease symptoms: after the fruit is infected, brown to dark brown round or nearly round lesions appear on the rind, with a sunken center and small black dots, sometimes forming concentric rings. When air humidity is high, pinkish protrusions form on the lesions. When there are many lesions, they can merge into patches, causing the fruit to turn black, rot or drop early. Leaf lesions are irregular, mostly strip-shaped. The leaf color at the lesions turns withered yellow, and severely affected leaves turn entirely yellow.
Conditions for onset: the disease generally occurs from June to August, and is severe in orchards with heavy rainfall, weak tree vigor, dense branches and leaves, and extensive management. The pathogen spores invade through wounds or natural openings.
Control methods: (1) Remove diseased branches, diseased fruits and diseased leaves and burn them in a centralized manner. Strengthen tree management and improve ventilation and light penetration. (2) When the rainy season arrives, spray Bordeaux mixture at 1:1:200 (copper sulfate:lime:water) once every 10-15 days to prevent the disease. (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, or 70% thiophanate at 800 times dilution, once every 15 days, for 2-3 consecutive sprays.
2. Walnut bacterial black spot disease
Disease symptoms: after the fruit is infected, small slightly raised dark brown spots first appear on the fruit surface, then expand into round or irregular black spots and become sunken, with no obvious margin and a water-soaked appearance around them; the fruit rots from the outside inward. After leaves are infected, small black dots first appear along the veins, then expand into nearly round or polygonal black spots; severe lesions merge into patches, causing shot holes.
Onset period: the disease generally occurs from May to August and can cause repeated infections. The pathogen invades through lenticels or wounds, and the disease is generally severe in hot, humid and rainy seasons.
Control methods: (1) Choose disease-resistant varieties, such as Gift No. 2, Xiangling, Fenghui, Shaanhe No. 1, etc. (2) Strengthen cultivation management; combined with pruning, promptly remove diseased fruits, diseased branches and diseased leaves, strengthen ventilation and light penetration, and improve tree structure. (3) Spray lime sulfur mixture at 3-5 degrees Baume once before bud break to eliminate overwintering pathogens. During the growing season, spray Bordeaux mixture at 1:0.5:200, or thiophanate-methyl or thiram wettable powder at 500-800 times dilution, 1-3 times (once each before female flowering, after flowering and at the young fruit stage); 50 mg/L streptomycin plus 2% copper sulfate can also be used, sprayed once every 15 days, with good results.
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