What is walnut branch blight? A complete guide to understanding it
What is walnut branch blight? How should it be prevented and controlled? Please advise. Walnut branch blight is caused by fungal infection and mainly damages branches and trunks. It occurs in all regions, with a general disease incidence rate of 20-30%, and in severe cases the incidence rate reaches more than 80%, causing a large number of branches to die, directly affecting tree growth and walnut yield...
What is walnut branch blight? How should it be prevented and controlled? Please advise.
Walnut branch blight is caused by fungal infection and mainly damages branches and trunks. It occurs in all regions, with a general disease incidence rate of 20-30%, and in severe cases the incidence rate reaches more than 80%, causing a large number of branches to die, directly affecting tree growth and the yield and quality of walnuts. Therefore, timely prevention and control are needed to control the disease, promote tree development, improve yield and quality, and increase benefits.
1. Symptom identification: Leaves on affected branches gradually turn yellow and fall off. The bark of diseased branches gradually loses its green color, initially turning grayish brown, then becoming light reddish brown to dark gray. The bark dries, cracks, and exposes the grayish brown xylem. When the lesion expands to encircle the branch or trunk, the branch dies, and even the entire plant may die.
2. Causes of the disease
1. Incomplete orchard sanitation. The pathogen overwinters on dead branches. In the spring of the following year, the pathogen spreads by wind, insects, and rain. The disease begins in May-June, and July-August is the peak period.
2. Inadequate management. First, insufficient water and fertilizer weakens the tree and reduces disease resistance, resulting in a high incidence rate; second, soil compaction leads to poor root development and reduced absorption function; third, mechanical wounds caused by careless operation during management facilitate pathogen invasion; fourth, late frost damage easily causes young trees and tender branches to become infected with this disease.
3. Shade within the orchard and poor ventilation and light penetration make branches grow tender and weak, making them prone to the disease.
3. Prevention and control methods
1. Thorough orchard sanitation. In winter, sweep up dead branches, fallen leaves, and diseased fruits in the orchard and take them outside the orchard to burn. Use 12.5 kg of quicklime, 0.5 kg of sulfur powder, 1.5 kg of salt, 0.25 kg of vegetable oil, and 50 kg of water to prepare a whitewash and apply it to the tree trunks in winter.
2. Strengthen management. First, deep plow the soil. After walnut harvest and before leaf fall, carry out deep soil plowing to mature the soil, promote root development, and improve absorption function. The suitable deep plowing depth is 20-30 cm. Second, apply sufficient fertilizer. Combined with deep plowing, apply 150-200 kg of decomposed organic fertilizer per mature large tree, and apply a nitrogen, phosphorus, and potassium compound fertilizer once in June-July. Third, irrigate promptly to promote robust tree growth and improve disease resistance.
3. Prune out dead branches. When diseased branches are found, prune them promptly and take them outside the orchard to burn. At the same time, do summer pruning well, thinning out dense branches, diseased and insect-damaged branches, and water sprouts to improve ventilation and light conditions and reduce the incidence rate.
4. Chemical control. From June to August, choose 70% thiophanate-methyl wettable powder at 800-1000 times dilution or mancozeb wettable powder at 400-500 times dilution for spray control. Spray once every 10 days, and 3-4 consecutive sprays can achieve obvious control effects. At the same time, promptly control trunk-boring pests such as the cloud-spotted longhorn beetle and the walnut small jewel beetle to prevent the pathogen from invading through borer holes.
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