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Prevention and treatment of susceptible diseases in the middle and later stages of corn
According to field monitoring, the current corn disease has reached its peak. It started on July 14th and lasted for 20 days. Prolonged hot and humid weather has created ideal conditions for the spread of high-temperature diseases. Specifically, the weather in the fields is favorable for several common diseases such as leaf spot, brown spot, curvularia leaf spot, and bacterial stalk rot. These diseases are now prevalent, and it's crucial to focus on prevention and treatment during the mid-to-late growth stages of the corn crop.
First, large leaf spot primarily affects the leaves, but can also invade the leaf sheath and the ear. The symptoms start as small lesions that rapidly develop into long, prismatic spots, sometimes reaching up to 10–30 cm in length. Lesions initially appear water-soaked, then turn blue-gray, and eventually become brown with dead areas. When humidity is high, black mold—comprising conidia and conidial stems—can grow on the lesions. This disease thrives between 26°C and 32°C, and low-lying fields with high plant density are more susceptible. The pathogen reproduces on the leaves and spreads through wind and rain. It prefers temperatures between 20°C and 28°C, and when air humidity exceeds 90%, the disease spreads quickly. However, temperatures above 25°C or below 15°C, along with humidity below 60%, suppress the disease. Continuous rain during the jointing to heading stage increases the risk of outbreaks.
Second, brown spot typically appears at the base of the leaves and the leaf sheath, but can also affect the stems. Initially, the lesions are yellowish-white and round, later turning brown or purple with a slightly raised, bubble-like appearance. A reddish ring often surrounds the lesions, and those on the midrib or sheath may be larger. The tasseling stage is the most vulnerable period for this disease, and there are noticeable differences among corn varieties. Brown spot thrives in temperatures between 23°C and 30°C, and rainy weather during the middle to late growth stages promotes its spread. High humidity and temperature further favor the disease.
For chemical control, you can use 20% Triadimefon EC diluted 3000 times or 12.5% Diniconazole powder mixed with 30g per 30kg of water.
Third, Curvularia leaf spot mainly affects the leaves, though it can also damage the leaf sheath and husk. It starts as small chlorotic spots that gradually expand into round, translucent areas. The center turns white to yellow-brown, while the edges become dark brown. There are often light yellow halos around the lesions, and symptoms vary greatly from plant to plant. Some plants may show only white or brown spots. This disease is another major threat following leaf spot. During the hot months of July and August, if there are 4–5 days of rain, the disease can spread quickly.
For control, apply 50% Tuzet WP diluted 1000 times or 12.5% Teptopol WP diluted 4000 times. Alternatively, use 70% Mancozeb WP at a 1000-fold dilution. Spray every 7–10 days, repeating 2–3 times for best results.
Fourth, bacterial stalk rot causes sudden wilting and death of plants during the mid-growth stage. The base of the stem near the soil surface shows yellow-brown to dark brown water-soaked lesions, which become soft and sunken, often emitting an unpleasant odor. This disease occurs during the tasseling stage, and it is favored by average temperatures of 30°C and humidity over 70%. Hot and wet conditions accelerate its spread.
To treat bacterial stalk rot, use 85% Trichloroisocyanuric acid diluted 3000 times, and repeat after 7 days.
Note: During the mid-to-late growth stages, diseases and pests often occur together on the same plant. Therefore, it’s important to choose pesticides that have multiple effects and can address both pests and diseases. For example, mixing an insecticide with a broad-spectrum fungicide like Diniconazole or Carbendazim can be effective. You can also add foliar fertilizers such as Penshibao, Duoxin, or potassium dihydrogen phosphate to enhance plant recovery and resistance. Apply these treatments once every 7 days, and continue for 2–3 applications for optimal results.