One, corn leaf spot

Maize leaf spot disease is a widespread leaf disease in the corn regions of the world. China's summer corn area is more serious than spring corn, and the year of pandemic can cause great losses. The lesions are mainly concentrated on the leaves, generally starting from the lower leaf and gradually spreading upward. The lesions were initially immersed in water and later turned yellow-brown or red-brown with darker edges. Lesions are elliptic, suborbicular or oblong, 10-15 mm long and 3-4 mm wide, sometimes with 2-3 concentric rings.

The temperature in July and August in North China is more than 25°C, which is most suitable for the epidemic. If there is more rainfall, more rainfall and higher temperature during this period, small spot disease will occur seriously.

Control methods: To promote the cultivation of Yuyu 11 and other disease-resistant high-product species, which can effectively reduce the occurrence of small spot disease. Strengthen cultivation management, apply compound fertilizer at jointing and heading stages to promote robust growth and increase plant resistance to disease. Clean the pastoral area, burned the diseased body and reduced the source of the disease. Chemical control, 50% Carbendazim WP 500 times, or 65% Mancozeb WP 500 times, or 70% thiophanate-methyl WP 500 times, or 75% 100% Bacterial clear wettable powder 800 times, or agricultural anti-120 water spray 100-120 times spray. From the end of the heart to the tasseling stage, spray once every 7 days and spray 2-3 times continuously.

Second, corn sheath blight

Rhizoctonia solani occurs in all parts of the country, and occurs in the mid-summer summer corn production areas. The disease can harm a variety of grass crops, such as cotton, soybeans and other dicotyledonous crops. The disease was immersed in leaf sheaths, leaves, ears, and temporal lobes. A watery, gray-green, near-circular lesion first appeared, and later became white, light yellow to red-brown mottled patches. When the temperature is high, white mold occurs on the lesions, and sclerotia are generated later. The color is white at the beginning and is dark brown after being cooked. The disease is mainly in the middle and late stages of corn growth. If the disease is long-term and cloudy after jointing, the disease is serious. Fertile soil, partial application of nitrogen fertilizer, overgrowth of plants, low-lying land, poor drainage, dew covered fields, high temperature (optimum temperature of 26-32°C) and high humidity (above 85% relative humidity) are all conducive to disease. If the temperature is lower than 20°C and drought occurs again (relative humidity below 75%), it is not conducive to the growth of pathogenic mycelium, and the pathogenicity is limited, and even the disease cannot be developed.

Control methods: remove the sick, destroy or deep-buried. Plant disease resistant varieties. Timely sowing, adding organic fertilizer or compound fertilizer containing humic acid to avoid partial application of nitrogen fertilizer, in case of more rain, pay attention to open drainage, reduce the humidity in the field, promote healthy growth of corn, improve resistance to disease. Chemical control, with 5% Jinggangmycin 1000 times, or 20% triadimefon EC 1000 times, or 50% carbendazim WP 500-800 times, or 40% saccaride 800 times, or 50% of the WP wettable powder 500-800 times, spray control, spraying should pay attention to the liquid sprayed on the stalk of the ear and below, in order to obtain a higher control effect.

Third, corn smut

Corn smut is an important disease in the national spring corn producing area. In the mountains in the northeast, north and central China, south China, southwest, and northwest, it is common, and it also harms some plants of the genus Sorghum and the genus Euphorbia. Only show symptoms in ears and tassels. The ear of the diseased plant became smaller and did not spit filaments. In addition to the temporal lobe, the whole ear turned into a large blackfly. In the later period, some eucalyptus leaves broke up with black powder, which is the teliospores of the pathogen. Black powder generally sticks into clumps and is not easy to fly. It is surrounded by filamentous parasitic vascular bundles.

Before the 3rd leaf stage of maize, the soil temperature was 21-28°C, and the humidity was most conducive to the intrusion of pathogenic bacteria at moderate drought. After the 4-5 leaf stage, the corn was less infected and the disease was not reinfected. When the seeds germinate, the germs also germinate, infect the seedlings, and with the growth of the plants, eventually destroy the panicles and become black powder. Continuous cropping, extensive farming, thick soil covering, and dry soil are all conducive to the onset of dissemination. The bacteria germinate long in the sorghum. Infestation of sorghum before 15 mm caused sorghum head smut.

Control methods: plant disease-resistant varieties, Zhongdan No. 2 and other hybrids more resistant. Timely removal of tumors or removal of diseased plants, clean the pastoral after harvest, reduce the initial infestation source, and avoid serious crops in severe wards to implement crop rotation. Rough cultivating, appropriate sowing, prompt seed buds early, unearthed faster, reduce the incidence. Chemical control, using a 0.5% seed amount of 15% triadimefon wettable powder, 0.8% 50% dexcone wettable powder, 0.2% 50% thiram wettable powder, or a 12.5% ​​alkene with 0.3% seed weight Oxazolol (Sully Poly) wettable powders are used for seed dressing.

Fourth, corn smut disease

Corn smut is a very common disease on corn and often damages young stems, leaves, ears and other tissues, resulting in tumors of different sizes. The early stage of the disease was silvery white, shiny, and rapidly enlarged, and the outer membrane ruptured later. After water loss, a large amount of black powder was emitted, namely the teliospores of the bacteria. The wintering of winter spores into the soil became the source of infection in the following year. The length of the tumor affects the fruit on the ear or it does not make it strong.

Control methods: selection of disease-resistant varieties, crop rotation, reduce the source of infection. Before and after heading, timely irrigation, avoid drought, timely control of corn borer, minimize insect damage or mechanical damage, to prevent the invasion of bacteria from the wound.

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