What are the control methods for sunflower brown spot?
How do you control sunflower brown spot? Please give guidance. Sunflower brown spot, also known as leaf blight, occurs widely across our country. In the early stage it can cause seedling death, and in the later stage it often causes premature leaf death, greatly affecting yield. In the early stage of seedling infection, nearly round lesions form on the cotyledons or young leaves, with a diameter of 2-6 mm...
How do you control sunflower brown spot? Please give guidance
Sunflower brown spot, also known as leaf blight, occurs widely across our country. In the early stage it can cause seedling death, and in the later stage it often causes premature leaf death, greatly affecting yield.
In the early stage of seedling infection, nearly round lesions form on the cotyledons or young leaves, with a diameter of 2-6 mm. The upper surface of the lesion is brown with a yellow halo around it, and the underside is grayish white. At the adult plant stage, irregular or polygonal brown spots form on the leaves, sometimes with a yellow halo around them; the center of the lesion is gray and scattered with small black dots, which are the pathogen's pycnidia. In severe cases the lesions merge into patches, causing the leaves to wither and die. The petioles and stems can also be affected, showing narrow brown streaks. Another leaf spot disease, called black spot, also frequently occurs on sunflowers. When diagnosing, note that black spot lesions are relatively larger, have concentric rings, and in humid weather produce brown mold-like growth on the lesions.
Sunflower brown spot overwinters as pycnidia on diseased residues, that is, those small black dots, or as mycelium. When suitable temperature and humidity occur in spring and summer, especially with continuous rainfall, the pathogen can release large amounts of conidia, which spread by wind and rain. Generally, the disease is more severe in continuous cropping fields, low-lying fields, and plots with heavier infection the previous year, and when the current year is rainy and field humidity is high.
To control sunflower brown spot, pay attention to the following points: rotate crops, carrying out a rotation of more than 3 years with grass-family crops; before cultivation, thoroughly remove diseased residual leaves and plow the soil deeply to reduce sources of inoculum; select disease-resistant varieties according to local conditions; strengthen field management, including reasonable close planting, use of fully decomposed organic fertilizer, balanced fertilization, timely sowing, and reasonable irrigation; after rain, drain field water promptly to reduce field humidity; in the early stage of disease, diseased leaves and bottom leaves can be removed by hand; 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 at 500 times dilution, or 70% thiophanate-methyl wettable powder at 1000 times dilution, or 30% basic copper sulfate (Lüdebao) suspension concentrate at 400-500 times dilution, or 50% benomyl wettable powder at 1500 times dilution. Generally, 1 or 2 applications are needed, with an interval of 10 days.
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