How to prevent and control walnut canker? A detailed explanation of prevention and control methods
Walnut canker is caused by a fungus, with spring and autumn being the two peak periods of the disease each year, and damage being most severe from mid-April to late May. Generally, walnut trees that are managed extensively, have thin and poor soil, poor drainage, insufficient fertilizer and water, weakened tree vigor, or have suffered frost damage and salt damage are prone to this disease. Let's take a look at the prevention and control methods for walnut canker below!
Symptoms of walnut canker
Walnut canker mainly affects branches and trunks, as well as the main trunk and side branches of young trees. In the early stage, the lesion is nearly spindle-shaped, dark gray, water-soaked and swollen; when pressed by hand, a foamy liquid flows out; the diseased bark turns brown and smells like distiller's grains; later the diseased bark loses water and sinks, and many small black dots are scattered on the lesion. When humidity is high, orange-red gelatinous material oozes from the small black dots; in severe cases, the lesion expands and causes the cortex to split longitudinally, exuding black water. In the early stage of infection on the main trunk, symptoms are hidden in the phloem and not easily seen from the outside; by the time symptoms are visible, the subcutaneous diseased area has already expanded more than 20-30 cm, exuding sticky black water that often smears on the trunk; later, black water flows out along the bark cracks, and after drying it becomes shiny, as if a layer of black lacquer had been painted on.
Occurrence pattern of walnut canker
The pathogen overwinters in the diseased parts as mycelium or stroma and pycnidia. After the sap begins to flow in the walnut tree the following spring, when suitable conditions for disease development occur, conidia are produced. The conidia are spread by wind, rain or insects and invade through grafting wounds, injuries and other openings, and the disease gradually expands after occurrence. Multiple infections can occur during the growing season, with spring and autumn being the two peak periods of the disease each year, and damage being most severe from mid-April to late May. Generally, walnut trees that are managed extensively, have thin and poor soil, poor drainage, insufficient fertilizer and water, weakened tree vigor, or have suffered frost damage and salt damage are prone to this disease.
Prevention and control methods for walnut canker
1. Strengthening tree management and enhancing tree vigor is the basic measure for preventing and controlling walnut canker. Through deep plowing to improve soil, cultivating and weeding, increasing the application of organic fertilizer, reasonable intercropping, timely irrigation and drainage, and reasonable pruning, the disease resistance of walnut trees is increased.
2. After harvesting walnuts, in combination with pruning, cut off diseased and insect-infested branches and scrape off diseased bark. At the same time, maintain good sanitation in the walnut orchard, promptly remove diseased branches and dead branches from the orchard, and burn them in a centralized manner outside the orchard to reduce the source of the pathogen.
3. Whitewash the walnut trunks, especially newly planted young trees, and pay even more attention to whitewashing the trunks in winter and summer to reduce channels for pathogen invasion. The whitewash formula is 12 kg quicklime, 1.5 kg salt, 250 g vegetable oil, 500 g sulfur powder, and 50 kg water.
4. In spring, thoroughly scrape off the lesions until new bark is slightly exposed. The scraping range should be about 0.5 cm wider than the discolored necrotic tissue. Apply 5-10 degrees Baume lime sulfur mixture or 1% copper sulfate solution, etc., to the scraped wounds, then burn the scraped bark and other material in a centralized manner.
5. Spray the canopy before the disease occurs or in the early stage of the disease. You can use 50% carbendazim wettable powder at 800 times dilution, or 75% chlorothalonil at 600 times dilution, or 50% thiophanate-methyl wettable powder at 1000 times dilution for spraying, once every 7 days, for 3 consecutive sprays.