How to prevent and control downy mildew in watermelon? A detailed guide to the latest control methods

Watermelon downy mildew tends to occur in the middle and late stages of watermelon plant growth. The disease mainly harms the leaves. At first, water-soaked light green small spots appear on the leaves, then they gradually turn yellow, and the lesions keep expanding and change from yellow to light brown. Because they are restricted by the leaf veins, they appear as irregular polygonal lesions. In severe cases, the lesions merge into patches and the leaves curl up.

Symptoms of watermelon downy mildew damage

Downy mildew mainly harms the leaves. It generally starts from the base leaves and gradually develops 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 become yellow-brown irregular polygonal lesions. In humid environments, black mold layers appear on the underside of the lesions. In severe cases, the lesions merge, and the entire leaf dries up and turns yellow-brown and breaks easily. 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 death.

Occurrence pattern of watermelon downy mildew

In the cold regions of the north, the pathogen cannot overwinter in open fields. After the plants wither, it dies, and the seeds do not carry the pathogen. 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 onset is 20-24°C, and invasion is easy when there is a water film on the leaf surface. It occurs easily and develops rapidly when humidity is high, the temperature is relatively low, and ventilation is poor.

Agricultural prevention of watermelon downy mildew

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

2. Cultivate disease-free strong seedlings, apply more organic base fertilizer, and pay attention to a reasonable combination of nitrogen, phosphorus, and potassium fertilizers.

3. After harvest, thoroughly remove diseased plants and fallen leaves.

Control methods for watermelon downy mildew

1. Agricultural control: Strictly discard diseased seedlings when transplanting. Choose plots with higher terrain and good drainage for planting. Apply sufficient base fertilizer, and do not apply too much nitrogen fertilizer during the growing period, so as to improve the disease resistance of the plants. The onset of the disease in plants is often related to an imbalance in the “carbon-to-nitrogen ratio” in their bodies. 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 50 ml, dilute with 15 kg of water, once every 7-10 days

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