How to treat powdery mildew on Euonymus japonicus? Detailed control techniques

Powdery mildew occurs commonly, affecting its ornamental value and restricting its use in landscaping.

Symptoms: Powdery mildew mainly harms the leaves of Euonymus japonicus, with lesions mostly distributed on the leaf surface, producing white powdery mold spots. When the disease is severe, the leaf underside and new shoots can also be affected, causing leaf shrinkage and deformation, new shoot distortion, atrophy and stunted growth, and causing leaf drop and shoot dieback. In the early stage of the disease, many small white round spots are scattered on the leaves; as the lesions gradually expand, they form irregular large spots, even covering the entire leaf surface. If the white powdery layer on the surface of the lesion is wiped off, yellow round spots can be found at the affected site.

Occurrence pattern: The pathogen overwinters as mycelium (that is, a gray film-like fungal layer) in the damaged tissues of Euonymus japonicus or between bud scales. In the spring of the following year, during the leaf expansion period and growth period of Euonymus japonicus, a large number of conidia are produced and spread by airflow to cause infection, becoming the inoculum source for the primary infection of the disease. The pathogen parasitizes on the surface of the host branches and leaves, producing haustoria that penetrate deep into epidermal cells to absorb nutrients; every spring, summer, and autumn it produces a large number of spores that repeatedly infect leaves and new shoots. High summer temperatures are the main factor in the occurrence of the disease.

Control measures:

1. Improve cultivation conditions. Choose plots with higher terrain, dryness, sufficient light, no water accumulation, and deep, fertile soil for cultivation.

2. Strengthen fertilizer and water management, apply more phosphorus and potassium fertilizer, and use an appropriate amount of nitrogen fertilizer; pay attention to drought resistance and drainage to make the seedlings grow robustly and improve disease resistance.

3. Prune reasonably and cut off diseased branches and leaves. Do a good job of winter garden cleaning, sweep up diseased branches and leaves and burn them in a centralized manner; during the growing period, promptly cut off and burn diseased leaves and branches when found, which can effectively reduce the primary infection inoculum source and re-infection inoculum source of the disease.

4. Use fungicides reasonably for timely control, and pay attention to alternating fungicides to avoid powdery mildew fungi developing resistance. Spraying should be uniform, and attention should be paid to spraying the inner canopy and leaf undersides. In winter, use lime sulfur mixture for control twice, with an interval of one month. During the leaf expansion period and growth period of Euonymus japonicus, especially from April to May and from September to October, the following fungicides can be selected for control: Bijunsha 800-1000 times solution, Penkejun 2000-3000 times solution, 25% Fenxiuning 800 to 1000 times solution, 70% Thiophanate-methyl 800 times solution, 50% Benlate 1000 to 1500 times solution, 50% Tuzet 800 times solution, etc.