Peanut focal spot disease has been heavier in recent years. In severe cases, the rate of diseased plants in the field can reach 100%. In an acute epidemic situation, in a very short period of time, a large number of peanut leaves can be caused to die, causing serious loss of peanuts.
symptom:
The disease usually produces two types of symptoms: focal spots and pepper spots. Common symptoms of focal spot type, usually from the tip of the leaf, a few from the edge of the leaf. The lesions develop in a wedge shape to the petiole, initially green, gradually yellowing and browning, and the edges are often dark brown with a yellow halo around them. The early stage of the disease is gray-brown, and many small black spots are formed on it. The disease is often mixed with leaf spot disease, and the leaf spot is contained in the wedge spot. Symptoms of the pepper spot type produce small lesions (less than 1 mm in diameter), irregular to round, and even depressed. Spots often appear on the front of the leaves. In the case of rain before harvest, the disease has acute symptoms. Large or irregular black-brown water-stained plaques are formed on the leaves, which rapidly spread to the whole leaves and develop to the petiole, stem and fruit needle.
Pathogens and occurrence rules:
Peanut focal spot disease is a fungal disease that occurs in the leaves. The pathogens overwinter in the diseased strains with hyphae and ascospores. The peak of ascospores spreads when the morning dew stops and begins to rain, the temperature is 25-27 °C, and the relative humidity is 70%-74%, which is beneficial to ascospores.
Control method:
Agricultural control: Adopting crop rotation, deep turning, burying diseased plant residues, proper early sowing, reducing density, covering the mulch and other measures have good control effects.
Chemical control: 1:2:200 times (copper sulfate: lime: water) Bordeaux mixture, or 75% chlorothalonil 500-800 times solution, or 70% mancozeb WP 300-400 times solution. The disease prevention and control index starts with the disease rate of 10%-15%, and the disease index starts at the first time. The disease is developed, and the disease is developed. It is sprayed once every 10-15 days, and the disease is sprayed 2-3 times.
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