Disease knowledge of Leaf spot of Rhododendron

Round spot, or irregular polygonal spot, dark brown, 1mm-5mm in diameter. In the later stage, the central tissue of the lesion turned gray. When the disease is serious, the disease spots are connected to each other, resulting in withered and yellow leaves and early fall. Under the moist environment, there are many brown mildew spots under the leaf spot, that is, the conidia and conidiophores of the pathogenic bacteria.

Pathogen and disease status: Cercospora CercosporarhocdodendriFer., Trichospora, Cercospora, Cercospora. The pathogen overwintered on the plant remains and formed conidia in the following year as the source of primary infection. The conidia are transmitted by wind and rain and invade from the wound. In Jiangxi, the disease began to occur in mid-May and reached its peak in August. In Guangzhou, the peak of the disease is from April to July, and the rhododendron cultivated in greenhouse can cause the disease every year. More Rain Water, more fog and heavy dew are conducive to the disease, because conidia can germinate only in water droplets. Poor ventilation and light transmission and poor plant growth can aggravate the occurrence of diseases. Prevention and control measures:

1. The fallen leaves were thoroughly removed and treated in autumn, and the diseased leaves were removed in time during the growing season.

2. The planting density of potted flowers is suitable in order to ventilate and penetrate light and reduce the humidity of leaves. In summer, potted flowers are placed in an outdoor shade to reduce wounds caused by sunburn and mechanical damage.

3. Immediately after enlightening, spray 65% Dyson zinc wettable powder 500Mel 600x liquid, or 50% carbendazim wettable powder 500Mel 800x liquid, or 70% methyl topiramate wettable powder 1000 times liquid. Spray once every 10-14 days for 3 times in a row.