What is rice leaf blast? How to prevent and cure it?

The blast that occurs on rice leaves is called leaf blast. The control of rice leaf blast should run through the whole growth period of rice, because the leaf blast can occur in the whole growth period, and the damage is serious from tillering to jointing stage. the epidemic of leaf blast directly affects the normal growth of rice, and in serious cases, the seedlings die, resulting in a reduction in rice yield or even no harvest.

1. Plaque type

Leaf blast occurs on seedlings or adult leaves after three-leaf stage, and generally occurs from tillering to jointing stage. the disease spots on leaves are often different in shape, size and color due to the difference of weather and disease resistance of varieties. it can be divided into four types: chronic type, acute type, white spot type and brown spot type, of which the former two kinds of harm are the most important.

Chronic plaque: rhomboid or spindle-shaped, generally 1 to 1.5 cm long, 0.3 to 0.5 cm wide, reddish brown to grayish white, with necrotic lines at both ends. Small dark green spots begin to appear on the leaves, gradually expanding into fusiform spots, often with extended brown necrotic lines. The center of the disease spot is gray-white, the edge is brown, there is a light yellow halo outside, and there is a gray mildew layer on the back of the leaf. When there are many disease spots, irregular large spots are formed, and this disease spot develops slowly.

Acute plaque: nearly round or irregular, dark green, dense gray mildew layer on the back of the plaque. Dark green near-round or oval disease spots were formed on the susceptible varieties, and brown mildew layers were produced on both sides of the leaves, which were not suitable for the transformation into chronic disease spots. The appearance of acute disease spot can be regarded as the forerunner of disease pandemic in the field.

White spot type disease spot: after the disease occurs in the susceptible young leaves, it produces white near round spots and does not produce spores. when the climatic conditions are favorable for its expansion, it can be turned into acute disease spots.

Brown spot type: it often occurs on highly resistant varieties or old leaves, producing needle-sized brown spots, only between veins and less sporulation.

two。 Prevention and control methods:

First, select disease-resistant varieties and pay attention to variety collocation and rotation.

The second is to treat rice seeds before sowing. 45% promethrin can be used to soak the seeds, apply grafting fertilizer and marriage medicine before transplanting, and apply urea 3-5kg per mu of seedling field one week before transplanting to enhance plant disease resistance, combined with the prevention and control of leaf rice blast and the delivery of borer and planthopper. You can also soak the seedlings with 20% tricyclazole wettable powder for 5 minutes, remove the heap and cover for 30 minutes before planting.

Third, reasonable fertilizer and water management, adequate application of basic fertilizer, early application of topdressing, proper application of nitrogen to control seedlings in the middle stage, and fertilization in the later stage. Avoid applying too much or too late nitrogen fertilizer, and pay attention to increasing the application of phosphorus and potassium fertilizer. Water management should be based on the principles of planting seedlings in shallow water, turning green in deep water, dividing iniquity in thin water, and drying the field enough.

The fourth is to carry out chemical prevention and control in time. Leaf plague should be detected and controlled as early as possible, and chemical control should be carried out in time if acute disease spots are found in the disease center or leaves from the tillering stage.

3. Common medicament

6% Chunramycin wettable powder 30-40 g / mu, or 75% tricyclazole wettable powder 30-40 g / mu or 40% Fuji No. 1 EC 100ml / mu. Spray 45-60 kg of water with any of the above chemicals, and control again after 8 days. Spray should be supplemented in case of rain within 4 hours after spraying, in order to achieve the ideal control effect.