Control method of downy mildew of chrysanthemum in autumn

Chrysanthemum downy mildew mainly damages leaves. In the early stage of the disease, pale yellow nearly round or polygonal disease classes grow on the old leaves of the lower part of chrysanthemum, gradually spread to the middle and upper part of chrysanthemum, and in the later stage, the disease classes become yellow brown. When they are seriously ill, the disease classes are even one piece, and the leaves are yellow and dead. When the humidity is high, white mold layer grows on the back of the sick class.

downy mildew of chrysanthemum

The suitable temperature for infection of downy mildew of chrysanthemum is 15~17℃ and the suitable humidity is above 85%. Autumn temperature difference between day and night, frosting time is long, foggy, rainy weather, etc., is the disease-prone period. In addition, planting too dense, too large a population, too much nitrogen fertilizer, poor ventilation and light transmission, too much fresh water, poor drainage, etc. will also aggravate the disease.

Agricultural control: rotate with non-Compositae vegetables for 2~3 years; plant density is reasonable, avoid over-dense, cover in the plant, which is not conducive to ventilation and moisture dissipation; apply base fertilizer heavily, increase organic fertilizer, control nitrogen fertilizer amount when topdressing, prevent excessive growth; avoid flooding, and drain water in time after heavy rain.

Chemical control: 35% metalaxyl can be used for seed dressing, and the dosage is 0.2~0.3% of the seed amount of chrysanthemum. Chrysanthemum long-term available 58% metalaxyl manganese zinc wettable powder 500 times solution, or 72% Ke Mei wettable powder 700 times solution, or 72.2% Pu Li Ke aqueous solution 1000 times solution, or 64% anti-alum-500 times solution, etc., 7~10 days spray once, continuous 2~3 times. Chlorothalonil fumigant can be used to fumigate chrysanthemum planted in the shed, with 350 grams per mu.