How to control black spot of walnut by leaf blackening and fruit rot

At present, walnut is in the early stage of ripening, walnut trees need more nutrition, but the north generally enters the rainy season, such as poor ventilation and light transmission in walnut orchards, which is easy to breed diseases, especially walnut bacterial black spot.

Black spot of walnut tree

1. Disease symptoms

Black spot disease of walnut trees, also known as black rot, mainly harms young fruits, leaves and twigs. The young fruit of walnut is infected with brown spots on the face, the edge is not obvious, and then blackens into pieces, reaching to the pulp, causing the whole walnut to blacken or rot and fall off; after the near-mature walnut is infected, the exocarp first affects the mesocarp, resulting in the exfoliation of the pericarp, the endocarp is exposed and the nucleolus is intact. When the leaf is infected, there are near round or polygonal small brown spots on the leaf veins. after expansion, they heal each other, water-stained halos appear in the periphery of the disease spots, a few perforations are found in the later stage, the diseased leaves are wrinkled and deformed, and when serious, the whole leaves become black and brittle and fall off.

2. The regularity of the disease

The pathogenic bacteria overwintered in the shoots or buds of walnut trees, and the bacterial liquid secreted in the second year was transmitted by wind and rain, invading from host stomata, lenticels, nectaries and wounds, causing disease in leaves, fruits or twigs. Under the condition of 4-30 ℃, the host epidermis was moist and the pathogen could invade leaves or walnuts. The incubation period in the field is 10-15 days. Walnut is easy to get sick in flowering and leaf spreading stage, and it is rainy in summer. The wound caused by the limb moth on the walnut tree is easily infected by this bacteria.

3. Key points of prevention and control

(1) Agricultural prevention and control: increase the application of organic fertilizer, reasonable irrigation and drainage, cultivate strong trees and improve the disease resistance of walnut trees; pay attention to the drainage and cleanliness of walnut orchards in summer and maintain good ventilation and light transmission.

(2) Chemical control: 72% agricultural streptomycin soluble powder 3000 times or 50% thiram wettable powder or 75% chlorothalonil wettable powder were sprayed on walnut trees during leaf expansion and after falling flowers. In addition, pests such as walnut limb moth should be controlled in time to reduce wounds.