Symptoms of watermelon downy mildew

Watermelon downy mildew only damages the leaves of watermelon. After infection, water-stained chlorotic spots appear on the leaves, and then develop into yellow spots. After expansion, they are restricted to polygonal yellow-brown lesions by leaf veins. When the disease is serious, the lesions are combined into a piece to make the leaves dry and curled. The disease spreads upward from the lower leaves, leaving only 3-5 pieces of young leaves at the top.

The watermelon downy mildew is caused by the infection of the pathogenic fungus of the genus F. genus, and the area where the melons are grown all the year round, the pathogens have no obvious wintering period. The germs spread through air and rain. In areas where no melons are grown in winter, the field bacteria can come from greenhouse melons or spread through air currents. In general, when the temperature difference between day and night is large, rainy, foggy, or dew, the disease is prone to epidemic. The watermelon in the protected area is heavier than the watermelon in the open field. The low-lying terrain, poor drainage, over-planting, extensive management, and poor ventilation have a serious incidence.

The pathogenic environment of watermelon downy mildew

In the cold regions of the north, the bacteria cannot survive in the open field, and the plants die after they have withered, and the seeds are not contaminated. The pathogens in the field mainly rely on airflow to invade from the stomata of the leaves. The occurrence of downy mildew is closely related to the temperature and humidity around the plant. The onset temperature is 20-24 °C, and it is easy to invade when there is a water film on the leaf surface. It is easy to occur when the humidity is high, the temperature is low, and the ventilation is poor, and it develops rapidly.

Watermelon downy mildew prevention

1 When agricultural measures are planted, the diseased seedlings are strictly eliminated; the land with high topography and well-drained land is selected for planting. Apply enough base Fertilizer, do not over-apply nitrogen fertilizer in the growing season to improve the disease resistance of the plant. The incidence of plants is often related to the imbalance of "carbon to nitrogen ratio" in the body, which enhances leaf nutrition and can improve disease resistance. The solution is prepared according to the ratio of urea: glucose (or white sugar): water = 0.5-1:1:100, 3-5 days. Spray once, even spray 4 times, the effect is very high.

2 agents for the prevention and treatment of downy mildew, such as: 70% ethyl phosphorus manganese zinc 500 times liquid, 72.2% Plex water 800 times liquid, 50% Fumei double wettable powder 500 times liquid, 75% chlorothalonil 700 Double solution, 25% metalaxyl WP 600 times solution, 20% benzox cream emulsifiable concentrate 300 times solution, 25% metalaxyl manganese Zn wettable powder 600 times solution, 50% nail cream copper WP 600 times solution 64% anti-virus WP WP 400 times solution, 70% nail cream aluminum copper 800 times solution, or 72% frost WP 660-800 times solution, 72% gram dew WP 750 times solution.