Powdery mildew is a worldwide disease and the host is very common. Lagerstroemia is one of its main targets of damage. Lagerstroemia powdery mildew is widespread in provinces and cities where crape myrtle is planted in China. After the onset of disease, crape myrtle leaves often become yellow and fall off, directly affecting tree vigor and indecent appreciation.
1 Implied symptoms Powdery mildew is a fungal disease, the primary risk leaf, and young leaves are easily infested than the old leaves. The disease is also at risk of shoots, shoots, flower buds and buds. At the beginning of the disease, white tiny spots appeared on the leaves, and when they expanded round, they were shaped as discolored patches. The upper layer was covered with a layer of white powdery mildew, and the later white powdery mildew layer turned gray. After the flowers are infected, the profile covers the white powder layer, the flower ear is deformed, and the disappearance goes to invaluable appreciation. The plants damaged by the powdery mildew will become short and the young leaves will be distorted, deformed and withered, the leaves will not develop, become smaller, and the branches will be deformed. When the plants become serious, the whole city will die.
2 Discipline of occurrence Lagerstroemia powdery mildew is the wintering of mycelium on diseased shoots, diseased shoots or fallen leaves. When the temperature adapts in the spring of the following year, the wintering mycelium begins to develop and develop, a large amount of conidia occurs, and the airborne dissemination occurs. Infection. In Tianshui Region, diseases generally begin in April and become severe in June. The July-August month will be slowed or curbed due to hot weather, but it may be re-issued from September to October. Powdery mildew occurs severely in the rainy season or under conditions of relatively high relative humidity. Partial application of nitrogen fertilizer, planted dense or ventilated, poor light transmission are all conducive to disease.
Prevention and treatment
1 Gardening prevention and control of crape myrtle has strong sprouting ability. Therefore, for severely diseased plants, all old shoots can be cut off in the winter and destroyed in a concentrated manner, thus thoroughly eradicating the root cause. If the potted crape myrtle in the family is found to be infected with powdery mildew, remove the diseased leaf in real time and place the potted flower in a ventilated and transparent place. In field cultivation, the planting density should be controlled, and daily management should be enhanced. Phosphorus and potash fertilizers should be added, and the application amount of nitrogen fertilizer should be controlled so as to increase the disease resistance of plants; at the same time, attention should also be paid to the selection of disease-resistant varieties.
2 When the chemical agent is used to prevent serious disease, it can spray Baume 3～4 lime sulfur before sprouting in the spring; when it develops seasonal disease, it can spray 80% zeocin zinc WP 500 times, or 70% thiophanate-methyl 1000% Doubling liquid, or 20% triadimefon (ie triadimefon) EC 1500 times, or 50% carbendazim WP 800 times.
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