How to prevent and control brown spot disease in sunflowers?
Sunflower brown spot disease, also known as leaf spot or blight, occurs over a very wide range in China. 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 infection in seedlings, nearly round lesions form on the cotyledons or young leaves, with a diameter of 2-6 mm. The front of the lesion is brown with a yellow halo around it,...
Sunflower brown spot disease, also known as leaf spot or blight, occurs over a very wide range in China. 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 infection in seedlings, nearly round lesions form on the cotyledons or young leaves, with a diameter of 2-6 mm. The front of the lesion is brown with a yellow halo around it, and the back is grayish white. When infection occurs at the adult plant stage, irregular or polygonal brown spots form on the leaves, sometimes with a yellow halo around them, and the center of the lesion is gray with scattered small black dots, which are the pathogen's pycnidia. In severe cases, the lesions merge into patches, causing the leaves to die. The petioles and stems can also be affected, forming narrow brown streaks. Another leaf spot disease, called black spot disease, also frequently occurs on sunflowers. When diagnosing, note that the lesions of black spot disease are relatively larger, have concentric rings, and when the weather is humid, brown mold-like material grows on the lesions.
Sunflower brown spot disease overwinters as pycnidia, that is, those small black dots, or mycelium on diseased plant residues. In spring and summer, when suitable temperature and humidity occur, 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 where the disease was severe the previous year, and in years with much rain and high field humidity.
To prevent and control sunflower brown spot disease, pay attention to the following points: rotate crops and change stubble, carrying out crop rotation with gramineous crops for more than 3 years; before cultivation, thoroughly remove diseased residual leaves and deep plow the soil to reduce sources of inoculum; select disease-resistant varieties according to local conditions; strengthen field management, including rational close planting, use of fully decomposed organic fertilizer, balanced fertilization, timely sowing, and rational irrigation, etc. After rain, promptly drain standing water from the field to reduce field humidity. In the early stage of disease, diseased leaves and bottom leaves can be removed by hand; for chemical control, the pathogen of sunflower brown spot disease 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, and 50% benomyl wettable powder at 1500 times dilution. Generally, 1 or 2 applications are needed, with an interval of 10 days.