Sunflower brown spot, also known as spot blotch, occurs in a wide range in our country. It can cause seedlings to die in the early stage, and it often causes the leaves to die prematurely, which has a great impact on the yield.
In the early stage of seedling development, near-round lesions are formed on cotyledons or young leaves, with a diameter of 2 to 6 mm. The lesion is brown on the front, with a yellow halo around it and a grayish white back. In the adult stage, an irregular or polygonal brown spot is formed on the leaves. There are sometimes yellow halos around the spot. The lesion is gray in the center and scattered with small black dots, which is the conidia of the pathogen. When severe, the lesions are contiguous and the leaves die. Petioles and stems can also be diseased, with brown, narrow stripe spots. Another leaf spot disease often occurs on sunflowers, called black spot disease. When the diagnosis is made, it should be noted that the lesions of melasma are relatively large, with concentric ring patterns, and when the weather is wet, brown molds are produced on the lesions.
The sunflower brown spot disease is caused by the conidia on the diseased body, that is, those small black spots or mycelium overwintering, and the appropriate temperature and humidity in the spring and summer, especially continuous rainfall, the germs can be able to distribute a large number of conidia. Wind and rain spread. In general, in heavy lands and low-lying lands, the incidence of heavier land mass in the previous year was heavier in the case of rainy days and high humidity in the fields.
Prevention and control of sunflower brown spot should pay attention to the following points: rotation crops, and crops for more than 3 years to implement crop rotation; thoroughly remove sick leaves before farming, deep soil, reduce bacteria source; Including rational dense planting, using fully decomposed organic fertilizer, balanced fertilization, appropriate sowing, reasonable irrigation, etc. After the rain, remove the water in the field and reduce the humidity in the field, and manually remove the diseased leaves and the bottom leaves at the early stage of disease; chemical control, sunflower The pathogen of brown spot is a relatively common fungus, many fungicides are effective for it, such as 50% carbendazim WP 500 times or 70% thiophanate-methyl WP 1000 times, or 30 Basic alkaline copper sulphate (Green Debao) colloidal suspension 400 to 500 times liquid, 50% benomyl WP 1500 times. Generally need to control 1 or 2 times, interval 10 days.
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