What are the control methods for watermelon downy mildew?

Watermelon downy mildew is prone to occur in the middle and late stages of watermelon plant growth. The disease mainly damages the leaves. Initially, water-soaked light green small spots appear on the leaves, which then gradually turn yellow. The lesions continue to expand and change from yellow to light brown. Because they are restricted by the leaf veins, they appear as irregular angular lesions. In severe cases, the lesions merge into patches and the leaves curl.

Damage symptoms of watermelon downy mildew

Downy mildew mainly damages the leaves, generally starting from the basal leaves and gradually developing upward to the upper leaves. In the early stage of the disease, yellow-green spots first appear on the leaves. After the lesions expand, they are restricted by the leaf veins and appear as yellow-brown irregular angular lesions. In humid environments, there is a black mold layer on the back of the lesions. In severe cases, the lesions merge, the entire leaf becomes yellow-brown and withered, and is easily broken. The leaves in the whole field turn yellow and withered, as if they had been scorched by fire. This disease is characterized by rapid onset and rapid withering.

Occurrence pattern of watermelon downy mildew

In the cold regions of the north, the pathogen cannot overwinter in the open field, and dies after the plants wither. The seeds do not carry the pathogen either. In the field, the pathogen mainly spreads through airflow and invades through leaf stomata. The occurrence of downy mildew is very closely related to the temperature and humidity around the plants. The suitable temperature for disease development is 20-24°C, and invasion is easy when there is a water film on the leaf surface. It is very likely to occur and develops quickly under conditions of high humidity, relatively low temperature, and poor ventilation.

Agricultural prevention of watermelon downy mildew

1. Properly control watering in the early stage of the disease. In protected cultivation, pay attention to enhancing ventilation and reducing air humidity.

2. Cultivate disease-free strong seedlings, increase the application of organic base fertilizer, and pay attention to the reasonable combination of nitrogen, phosphorus, and potassium fertilizers.

3. Thoroughly remove diseased plants and fallen leaves after harvest.

Control methods for watermelon downy mildew

1. Agricultural control: Strictly eliminate diseased seedlings when transplanting. Choose plots with higher terrain and good drainage for planting. Apply sufficient base fertilizer, and do not apply excessive nitrogen fertilizer during the growing period, so as to improve the disease resistance of the plants. Plant disease occurrence is often related to an imbalance in the "carbon-to-nitrogen ratio" in the plant body. Strengthening leaf nutrition can improve disease resistance. Prepare a solution in the ratio of urea:glucose (or brown sugar):water = 0.5-1:1:100, spray once every 3-5 days, for 4 consecutive sprays. The control effect is very good.

2. Chemical control

① Prevention: Aolike Shuangbeier 50ml, dilute with 15 kg of water, once every 7-10 days

② Treatment: Aolike Shuangbeier 50ml + garlic oil 15ml, dilute with 15 kg of water, use once every 3 days, for 2-3 consecutive times.