How does impatiens suffer from powdery mildew?

[distribution] it happens all over the week.

[symptoms] the disease mainly occurs on leaves and shoots, and seriously harms buds and capsules. The disease began in Beijing after June, and after July, the leaf surface was gradually covered with white powder layer, and gradually expanded to the whole leaf covered with white powder layer. In the later stage, yellow dots were formed on the powder layer, and the color gradually deepened and became dark brown, which was the closed capsule of the pathogen and was spherical under the magnifying mirror. The dark brown dots mainly appeared on the front of the leaves and the small dots on the back of the leaves were rare. In severe cases, the leaves withered and fell early. The disease in Shanghai is generally more serious after flowering. The damaged plants were short and small, the tender shoots were curved, the leaves were uneven and the flowers were deformed.

[pathogen] the pathogen is fungal, monocystic shell (Sphaerothecabal-saminae), the closed capsule is spherical to subglobose, accessory hyphae, the closed capsule contains 1 ascus, the ascus is short oval or oval, contains 8 ascospores, ascospores are oval, colorless, unicellular.

[incidence regularity] the pathogen overwintered on the diseased remains with closed cysts, ascospores and conidia. Spread by the wind. The disease was more serious in Shanghai after flowering, and the fallen leaves appeared in October. According to records in Beijing, seedlings could be infected when the temperature was above 20 ℃, and the leaves were gradually covered with white powder layer after July. Powdery mildew is easy to occur when the temperature is high, the light is little, the ventilation is poor and the air humidity is high.

[prevention and control methods]

(1) Horticultural control: do not plant too densely, properly ventilate, strengthen light; in order to improve disease resistance, it is necessary to apply more phosphate fertilizer. After the end of the flowering period, the residual plants were pulled out, the fallen leaves were removed and destroyed in time. Cut off the disease in time or remove the disease completely and destroy it.

(2) Drug control: spray 4000 times solution of 20% trimethoprim or 70% methyl topiramate 1000~l500 solution during the onset of the disease. Avoid spraying at a high temperature above 32 ℃ to avoid drug damage.