The leaf spot diseases that occur during the growing season of maize include: large spot disease, small spot disease and brown spot disease. In some areas, gray spot disease, leaf spot caused by Curvularia, rust and anthracnose may occur.
Differentiating several diseases can focus on the following aspects. The first is the size and shape of the lesion. Corn spot disease has the largest lesions, long fusiform shape, 5 to 10 cm long, and several lesions of other diseases are relatively small. For example, the spot size of small spot disease is only 1 to 2 cm, gray spot and Curvularia The spot length of mold leaf spot is 0.5 mm to 3 cm, which is oval, and the lesions of rust and anthracnose are only a few millimeters. However, what we often see is that several lesions heal together, and the shape and size are very irregular. From the color of the lesion, the brown spot is the deepest, brown or purple-brown, the rust summer spore heap is yellowish brown, the gray spot disease is light gray, and later becomes taupe or yellowish brown, and the others are mostly in the middle of the lesion. It is dry white, with dark brown edges and a pale yellow halo around it. In the late growth stage, some organs that transmit diseases can be produced. For example, many small black spots (which can produce conidia) grow on the lesions of anthracnose, and rust leaves a yellow-brown powder (siasporium powder), brown spot disease. The tissue is broken and the brown powder (sleeping sporangia) is scattered. When the weather is wet, the surface of the lesions can grow with different color of the mildew. The big spot is black, the small spot is brown, and the gray spot is gray. Gray.
The occurrence of several diseases is generally similar. The pathogens are overwintered by diseased bodies. The disease spreads from the lower leaves. The high temperature and high humidity weather is conducive to disease prevalence. Therefore, the following measures can be uniformly adopted for prevention and treatment: selection of disease-resistant varieties; removal of diseased plant residues, including removal of lower diseased leaves in the early stage of the disease, removal of field straws during harvesting season, and deep cultivation of mites; implementation of rotation, rational close planting, timely early sowing, and application of organic fertilizer Improve the level of cultivation and management; take timely drug control in the early stage of the disease. The following agents can be used alternately: 50% carbendazim wettable powder 500-600 times solution, 75% chlorothalonil wettable powder 600-800 times solution, 65% daikon zinc wettable powder 400-500 times solution, and A A drug such as thiophanate-methyl (methyl thiophanate), propiconazole, oxazolidine (Shigao), chlorfenapyr (staple, sapphire).
(Senior Consultant of Sinofert, Professor of China Agricultural University, Xiao Yueyan)
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