Corn is the main food crop in China, and its planting area and total output are second only to wheat and rice. At present, the common serious diseases are big leaf spot, small leaf spot, rust, sheath blight, Curvularia leaf spot, stem base rot, head smut and so on.
leaf blight
Maize leaf blight, also known as stripe disease, coal stripe disease, leaf blight and leaf spot disease, is the main leaf disease of maize, which occurs all over China and is very harmful.
It mainly harms leaves, and can also harm leaf sheaths and bracts in severe cases. Generally, it starts from the bottom blade and gradually expands upward. In severe cases, it can spread throughout the whole plant, but there are also cases of middle and upper leaves.
Leaf spot
Corn leaf spot can occur from seedling stage to mature stage, which mainly harms leaves, but also harms bracts and seeds of stems and ears.
Leaf lesions are small and numerous, which are brown waterlogged spots at first, and then expand into oval or rectangular lesions about 0.5 cm, with purple or red halo on the edge.
The lesions on leaf sheaths and bracts are generally spindle-shaped or irregular, yellow-brown, with purple-black or inconspicuous edges. The diseased part is often covered with a layer of gray-black mold, which sometimes causes the ear to rot or droop and the seeds to turn black.
Curvularia leaf spot
Curvularia lunata is another new leaf disease after the large-scale planting of corn, which is widespread in the main corn producing areas in China.
brown spot
The first is prevention in advance. Spraying 15% triadimefon wettable powder 1000 times solution can prevent the occurrence of corn brown spot; The second is timely prevention and control.
In mid-July, after the first rainfall in Wang Mi area of Huangzhuhai, triadimefon, thiophanate-methyl and diniconazole were sprayed on the whole plant.
When corn is diseased, 25% triadimefon wettable powder 1500 times, 50% chlorpheniramine wettable powder 1500 times, and 12.5% woluolihuohao alcohol wettable powder 1000 times can also be sprayed on the leaves.
In order to improve the control effect, foliar fertilizers, such as foliar fertilizer, potassium dihydrogen phosphate, urea, etc., can be properly added to the liquid medicine to promote the health of corn and improve its disease resistance.
Southern rust
Rust mainly affects leaves, and can also occur on panicle bracts and male flowers in severe cases. The middle and upper leaves of plants are seriously ill.
At first, there are scattered or inconspicuous yellowish spots on the front of the leaves, and then they are prominent and expanded into round to oblong, yellowish brown or brown, and the surrounding epidermis is turned up and rusty powder is scattered. In the later stage, a round black protuberance grew on the lesion, and after rupture, dark brown powder was exposed.
banded sclerotial blight
Corn sheath blight mainly harms leaf sheaths and stems, and causes ear damage in severe cases. At the early stage of the disease, dark green waterlogging spots were mostly produced on the leaf sheaths of the basal stems of 1-2, and then they expanded into irregular or moire spots.
The center of the lesion is grayish brown, and the edge is dark brown, extending from bottom to top in each eye. Fringe leaf disease also produces the same moire spots. After the onset of otopathy, the ears are bald and the seeds are thin, flat or brown.
In severe cases, the rhizome tissue turns gray, and the secondary roots are yellow-brown or rotten. When it is rainy and high humidity lasts for a long time, the disease grows dense white hyphae, which further aggregate into multiple hyphae and form small sclerotia.
Stem rot
1. Seed dressing with chemicals, 25% triadimefon wettable powder 100- 150g, seed dressing with 50Kg of water or seed coating agent can effectively reduce the occurrence of stem rot.
Second, rhizomes can be sprayed at the early stage of the disease, and10 is sprayed every 7 days, with 50% of the wettable powder of sukeling, 1000 of the wettable powder of mancozeb, 500 times of the wettable powder of carbendazim and 500 times of the wettable powder of methyl sulfate.
Head smut
Head smut of corn, also known as black rice and dumb corn, is an important disease in spring corn region of China. It mainly harms the female ear and the male ear of corn. Most of them have symptoms after heading, but some inbred lines have symptoms at seedling stage, and 4-5 leaves have 1-4 yellow-white stripes.
Female ear is shorter than healthy ear, the lower part is swollen, the top is sharp, and the whole ear becomes a mass of dark brown powder and many scattered black filaments. Some proliferate and become green branches; Some bracts become narrow, clustered, deformed, with less black powder and more tillers.
Ear rot
Ear rot of maize is one of the important diseases in the late growth period of maize, also known as ear rot of maize, which is a worldwide disease. The incidence of common varieties is 5%- 10%, and the incidence of susceptible varieties can reach about 50%, causing serious losses.
From the top or base of the ear, the disease begins, and a large area or the whole ear rots, and the diseased particles are shriveled, dull and not full. Sometimes there is pink or grayish white mycelium between grains, which is densely covered with red powder, and the diseased grains are easily broken.
The bracts of the diseased ear are penetrated by dense hyphae, and they stick together and are not easy to peel off.
Tumor black powder
Seed dressing with 50% thiram wettable powder is 0.2% of the seed weight, or 50 kg with 20% triadimefon emulsion 200ml, or 0.5%-0.7% with 50% carbendazim wettable powder.
Spraying 50% carbendazim or 5% thiram before heading. Controlling 1-2 times can effectively alleviate the disease. Because of the long initial infection time of maize head smut and pesticide residues, the control effect of spraying pesticides in maize growth period is often not ideal.