Control of sunflower brown spot

Sunflower brown spot, also known as spot blight, occurs widely in China, which can cause seedling death in the early stage and premature leaf death in the later stage, which has a great impact on yield. At the initial stage of the disease, nearly round disease spots were formed on the cotyledons or young leaves, with a diameter of 2-6 mm. The lesion is brown on the front, surrounded by a yellow halo, and grayish white on the back. In the adult stage, the disease forms irregular or polygonal brown spots on the leaves, sometimes surrounded by yellow halo rings, gray in the center of the disease spots and scattered black spots, that is, the conidia of pathogens. In severe cases, there are a series of disease spots, which withered the leaves. Petioles and stems can also be diseased, with brown narrow spots. Another kind of leaf spot disease often occurs on sunflowers, called black spot. When diagnosing, it should be noted that the spot of black spot is relatively large, with concentric wheel lines, and brown mildew occurs on the spot when the weather is wet. Sunflower brown spot disease overwinters with conidia on the diseased remains, that is, those small black spots or hyphae. When appropriate temperature and humidity are encountered in spring and summer, especially continuous rainfall, the pathogen can distribute a large number of conidia and spread by wind and rain. Generally in the continuous cropping land, low-lying land, the land where the disease was more serious in the previous year, the disease was more serious when it was rainy and the field humidity was high. The following points should be paid attention to in the control of sunflower brown spot: crop rotation, rotation with Gramineae crops for more than 3 years; thorough removal of diseased and residual leaves before cultivation, deep turning of soil, reduction of bacterial source; selection of disease-resistant varieties according to local conditions Strengthen field management, including reasonable close planting, use of fully mature organic fertilizer, balanced fertilization, suitable sowing, reasonable irrigation, etc., timely elimination of stagnant water in the field after rain, reduction of field humidity, and manual removal of diseased leaves and bottom leaves in the early stage of the disease. For chemical control, the pathogen of sunflower brown spot is a relatively common fungus, and many fungicides are effective against it, such as 50% carbendazim wettable powder 500 times or 70% thiophanate methyl wettable powder 1000 times, or 30% basic copper sulfate (Lvdebao) suspension 400 times 500 times, 50% carbendazim 1500 times. It is generally necessary to prevent and cure it once or twice at an interval of 10 days.