First of all, symptoms

The disease mainly harms leaves, branches, branches and fruits. On young leaves, the lesions are brown and polygonal. On the old leaves, the lesions are round, the center is grayish brown, and there are sometimes yellow halo around them. Sometimes the grayish brown part of the center forms a perforation, and in severe cases, the lesions are connected with each other. The edge of the petiole is sometimes brown, the middle is gray, and there are yellow halo around it. The lesion on the shoot tip is long, brown and slightly concave. In severe cases, the lesion surrounds the branches, causing the upper part to die. At the early stage of fruit disease, small brown spots appeared on the surface of fruit, and the edges of the spots were unclear, which gradually expanded to form nearly round or irregular dark-painted spots, sinking or not. On rainy days, there are obvious water stains around the diseased spots. The young fruit is sick, and bacteria invade the nucleolus, which makes the nucleolus rot. After the fruit grows to a medium size, it is infected, and the lesion is limited to the exocarp, but the growth of nucleolus is blocked and shriveled after harvest.

Second, the law of occurrence

The pathogen overwinters in the diseased parts of branches and stems with umbilical cord or mycelium. The conidia produced in the next spring when the conditions are suitable are first impregnated by wind and rain and insects in wounds or twigs, and then spores are produced after the onset of the disease for re-impregnation. May-June onset, July-August peak onset, and stop after September. Young trees are easy to get sick in rainy years with high air humidity. This fungus is a kind of weak parasitic fungus, which is easy to get sick on weak walnut branches, especially in spring drought or frozen years.

Third, prevention and control methods

1. Strengthen the management of cultivated soil in walnut orchard, increase the application of organic fertilizer, biological fertilizer and mineral fertilizer, enhance the tree vigor, reduce the bacterial source base and improve the disease resistance.

2. Thoroughly remove diseased leaves, branches and fruits, burn them centrally or bury them deeply, and remove the source of infection.

3, reasonable pruning, reduce dense coverage, improve ventilation and light transmission conditions. Pruning of walnuts should be done after leaf spreading and before defoliation. It is not advisable to cut and saw branches during dormancy to avoid bleeding and tree death.

4. Chemical control. Spraying 3 ~ 5 Baume lime-sulfur mixture before germination. Spray 1︰2︰200 bordeaux solution before onset. Spraying 70% thiophanate-methyl 800 times +25% propiconazole 4000 times or 70% thiophanate-methyl 500 times +72% agricultural streptomycin 1500 times in the whole garden after onset, every 7 days 1 time, the two dosage forms are used alternately for 2 ~ 3 times.