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: first, the size and shape of the lesion. Corn spot disease has the largest lesions, long fusiform, 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 to 3 cm, which is oval, and the lesions of rust and anthrax are smaller, only a few millimeters. However, what we often see is that several lesions heal together, and the shape and size are also 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 ruptured and brown powder (sleeping sporangia) is released. When the weather is wet, the surface of several lesions can grow a variety of mold layers, black of large spot disease, brown of small spot disease, gray of gray spot disease.
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 to prevent and control: 1. Select resistant varieties. 2. Remove the residue of the diseased plant, including removing the lower diseased leaves in the early stage of the disease, clearing the field straw during the harvesting season, and deep-cultivating the mites. 3. Implement rotation, rational close planting, timely sowing, increase application of organic fertilizer, and improve cultivation management. 4. 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% daisen zinc wettable powder 400~500 times solution, and A A drug such as thiophanate-methyl (methyl thiophanate), propiconazole, oxazolidine (Shigao), chlorfenapyr (staple, sapphire).
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