Symptoms and control of walnut rot

   1. Distribution and occurrence characteristics, also known as Blackwater disease, occurred in Henan, Shanxi, Shandong, Sichuan and other places. The pathogen overwintered in the diseased part with mycelium or sporangium and conidium. After the walnut sap flowed in the next spring, conidia were produced under suitable conditions. The conidia were transmitted by wind, rain or insects, and invaded from the grafting interface, shearing saw mouth, wound and so on. The disease spread gradually after the disease occurred and did not stop until before overwintering. Multiple infections can occur during the growing period. Spring and autumn is the peak of the disease in a year, especially from mid-April to late May. Generally, walnut trees with extensive management, barren soil layer, poor drainage, insufficient fertilizer and water, weak tree potential or suffering from freezing injury and saline-alkali damage are easy to be infected with this disease. When the air humidity is high, the infection can be done many times until the infection stops before overwintering.

   2, pathogen and damage symptom is a kind of fungal disease, which is caused by cyst of walnut shell. The incidence of seriously injured walnut plants can reach more than 80%. The big branches of the diseased tree gradually withered, and in severe cases the whole tree died.

   is mainly harmful to branch bark, and its disease symptoms are also different due to different tree age and susceptible parts. After the tree trunk is susceptible, the disease spot is hidden in the cortex at the initial stage, commonly known as "wet bark". Sometimes multiple plaques form large patches, surrounded by a large number of white mycelium, overflowing with black mucus from the degree layer. In the later stage of the disease, the lesion can be extended to 20 to 30 centimeters long. The bark is split longitudinally and shines after the black water dries out along the cracks in the tree. After the trunk and lateral branches of the young trees were damaged, the disease spot was nearly fusiform in the initial stage, showing dark gray, water stains, and slightly swollen, pressing the disease part with fingers, and flowing out foamy liquid. There are many black dots scattered on the spot, that is, the conidium of the pathogen. When the air humidity is high, orange glial filamentous horns gush out from the small black spots. The disease spot developed along the vertical and horizontal direction of the tree trunk, and in the later stage, the cortex of the disease spot longitudinally cracked and a large amount of black water flowed out. When the disease spot surrounded the tree trunk for one week, it led to the lateral skill of the young tree or the death of the whole plant. The damage to the branches mainly occurred on the vegetative branches or 2-3-year-old lateral branches, the susceptible parts gradually lost green, the cortex and wood peeled off rapidly, the whole branch withered, and the conidium with black spots scattered on the disease spot.

   3. Prevention and control methods

  ① curettage for plaque. As in early spring, plaques can also be found during the growing period for curettage at any time. After scraping, smear and disinfect with 50% methyl topiramate wettable powder 50 times solution, or 50% bacillus wettable powder 50 times solution, or 5% 10 Baomedu stone sulfur mixture, or 1% copper sulfate solution, and then apply Bordeaux solution to protect the wound scar, preferably scraped into a Tsuen shape, the scraping should be smooth and smooth to facilitate healing. The scope of scar scraping should be about 1 cm beyond discolored necrotic tissue.

After   ② harvest, combined with pruning, cutting off disease and insect branches, scraping diseased skin, collecting and burning, reducing the source of bacterial infection. The trunk is painted white in winter to prevent the rot caused by freezing injury and insect pests.

  ③ chemical control. Using Fuxing 1000 times solution + Kangfubao 100 times solution for wound disinfection, the first time from March to April, the second time from July to August, and the third time after harvest can effectively prevent the occurrence of rot. The commonly used disinfectants include 100 ~ 150 times of Jubiqing, 30 ~ 50 times of Shiduqing, etc., and the effect is good.