The Latest Control Methods for Watermelon Powdery Mildew
Powdery mildew is a common disease of watermelon, distributed in all watermelon-producing areas across the country, occurring on both spring and autumn watermelons in the south, but more severely on autumn watermelons, while open-field watermelons in the north develop the disease in summer, and in protected areas such as greenhouses and plastic tunnels the disease can occur year-round. The plants can be infected throughout the entire growth period, but the disease occurs most severely in the middle and late stages of growth. Let us take a look at the control methods for watermelon powdery mildew below!
Damage Symptoms
Watermelon powdery mildew mainly damages the leaves, followed by the petioles and stems, and generally does not harm the fruit. In the early stage of the disease, white nearly circular star-shaped small powdery spots appear on the leaf surface or the underside of the leaf, mostly on the leaf surface. When environmental conditions are suitable, the powdery spots rapidly expand and connect into patches, becoming large areas of white powder with indistinct edges, covered with white powdery mold. In severe cases, the entire leaf surface is covered with white powder. There is less white powder on the petioles and stems. The disease gradually spreads from old leaves to new leaves. In the late stage of the disease, the white mold layer turns gray as the hyphae mature, and the diseased leaves turn yellow, curl up, and generally do not fall off. When environmental conditions are unfavorable for the reproduction of the pathogen or the host ages, clusters of yellow-brown small granules appear on the lesions, which later turn black.
Occurrence Conditions
The occurrence and epidemic of watermelon powdery mildew are closely related to temperature and humidity and cultivation management. In terms of cultivation management, fields planted too densely with poor ventilation and light transmission are prone to the disease. With excessive nitrogen fertilizer, excessive vegetative growth of plants, soil water shortage, and untimely irrigation, the disease develops rapidly and is severe. Watermelon fields with excessive irrigation, increased humidity, low-lying terrain, poor drainage, or close to protected areas such as greenhouses and tunnels also have severe disease. Different growth stages of watermelon have different resistance to powdery mildew; generally, the tender leaves at the seedling stage or adult plant stage have strong disease resistance.
Control Methods
1. Plant at a reasonable density and adopt the planting method of high beds and deep furrows, cover the beds with plastic film, focus on strengthening field management after the fruiting stage, prune reasonably, and remove severely diseased leaves and some old leaves in a timely manner to facilitate ventilation and light transmission, reduce field humidity, and reduce repeated infection by the pathogen.
2. Grasping the characteristic that watermelon loves water but fears water, adopt an alternating dry and wet irrigation method, pay attention to drainage after rain, prevent the watermelon field from being soaked and waterlogged, and after continuous rainfall, apply pesticides as soon as it clears to prevent the disease from rapidly spreading in the watermelon field.
3. Do a good job in fertilization, mainly using organic fertilizer, adopting a fertilization method combining organic and inorganic fertilizers, and applying nitrogen, phosphorus, and potassium in combination. For topdressing in the late stage of watermelon, compound fertilizer should be the main choice, and urea should be applied as little as possible or not at all, so as to improve the disease resistance of the plants.
4. Strengthen cultivation management, pay attention to the combined application of nitrogen, phosphorus, and potassium fertilizers, and prevent excessive application of nitrogen fertilizer. Cultivate robust plants. Pay attention to timely plant adjustment to prevent leaves and vines from being too dense and affecting ventilation and light transmission. Promptly cut off diseased leaves and burn them to prevent spread.
5. The key to chemical control of watermelon powdery mildew is to do a good job of applying pesticides in the early stage of the disease. If the disease continues to develop after application, spraying should be done with sufficient water, the underside of the leaves should also be sprayed, and the entire field should be sprayed evenly to prevent missed spraying.