What are the control methods for black spot disease in chrysanthemums?
How do you control black spot disease in chrysanthemums? Please note that the pathogen is Septoria chrysanthemella. Also known as brown spot and leaf blotch. It is a serious disease of chrysanthemums and occurs everywhere. Symptom characteristics: on infected leaves, purplish-brown spots of round, oval or irregular shape and varying size first appear, and later...
How do you control black spot disease in chrysanthemums? Please explain
The pathogen is Septoria chrysanthemella. Also known as brown spot and leaf blotch. It is a serious disease of chrysanthemums and occurs everywhere.
Symptom characteristics
On infected leaves, purplish-brown spots of round, oval or irregular shape and varying size first appear, and later turn dark brown or black, 2-10 mm in diameter. The boundary between the infected part and the healthy part is distinct; in the later stage the center of the spot becomes lighter, appearing grayish-white, with fine small black dots. In severe cases only the top 2-3 leaves remain disease-free, and the diseased leaves wither prematurely, but do not fall off immediately and hang on the plant.
Disease development pattern
The pathogen overwinters as mycelium and pycnidia on diseased plant debris, becoming the source of infection for the following year; the pycnidia release large numbers of conidia, which are spread by wind and rain. Rainy autumn weather, high planting density and poor ventilation all favor the occurrence of the disease. Disease resistance differs among varieties; for example, Zihe and Yuanyang are relatively resistant, while Guangdong Huang is the most susceptible. Plants propagated by division are severely affected, while those grown from cuttings taken from the upper buds of vigorous plants are less affected.
Control methods
① For small-scale planting, remove diseased leaves by hand and burn them in a centralized manner.
② Improve the growing environment. In areas with severe disease, practice crop rotation; do not plant too densely, so as to allow ventilation and light penetration, and drain standing water promptly.
③ During the disease period, spray with Bordeaux mixture at 100-150 times dilution or 80% Captan wettable powder at 500 times dilution; you can also spray a mixture of 50% Thiophanate-methyl at 1000 times dilution and 80% Captan at 500 times dilution, or spray 45% chlorothalonil and carbendazim mixed suspension concentrate at 1000 times dilution; the effect is better than using a single agent.
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