Watermelon leaves turn yellow. Is this bacterial injury or insect pest? Some leaves have small black spots on the back, and insects are suspected. Those without small black spots on their backs will t

Watermelon leaves turn yellow. Is this bacterial injury or insect pest? Some leaves have small black spots on the back, and insects are suspected. Those without small black spots on their backs will turn yellow. What medicine should I take? Causes and preventive measures of yellow leaves of watermelon

First, herbicide damage causes yellow leaves.

Watermelon is a kind of millet. Generally speaking, selective herbicides are used after seedlings. When transplanting, strictly control the operation sequence, spray herbicides on the flat land, and then dig holes for planting. In this way, when planting, the soil layer with herbicide on the soil surface can be uncovered to avoid the damage of watermelon root system. Watermelon is planted in small arch shed mode in northern protected areas. When using herbicides, double films are used as far as possible, that is, a plastic film and an arch shed film. In this way, the plastic film can effectively inhibit the odor of herbicide transpiration under the film without affecting the growth of watermelon. It should be especially cautious to use herbicides in the way of one film and two purposes, such as arch shed in the early stage and local film in the later stage. In a closed environment, steam transpiration and herbicide fumigation will inhibit the growth of watermelon seedlings and make the leaves yellow. Prevention and treatment methods: first, timely ventilation; The second is to choose the appropriate compound beneficial microbial inoculum, and water it after root irrigation. (It is generally not recommended to use herbicides in watermelon planting)

Second, improper root burning of fertilizer causes yellow leaves.

In order to obtain high yield of watermelon, melon farmers tend to focus on applying chemical fertilizer, excessive application of chicken manure, especially watermelon in greenhouse, and more application of manure. Because of the application of immature human and animal manure, or long-term application of chemical fertilizer, chemical fertilizer will hurt the roots. Some also use foliar fertilizer too much. Because many foliar fertilizers contain hormones, watermelon hormones and trace fertilizers are poisoned, which makes the leaves become stiff, green, brittle and deformed, and the leaves and leaf sheaths turn yellow. Prevention and control methods: first, it is forbidden to use immature human and animal feces, and it must be fully fermented in advance before application; Second, when applying chemical fertilizer, it is best to use formula fertilization, appropriately increase phosphorus and potassium fertilizer, and when using base fertilizer, it is not advisable to use too much nitrogen fertilizer to prevent root burning; Third, if the fertilizer is found to burn roots, it should be irrigated with microbial agents in time, 5- 10 kg per 667 square meters, and then washed with water. For the rotten roots and yellow leaves caused by the application of raw fertilizer, the method of broken film ventilation should be adopted to reduce gas damage.

Third, the lack of elements leads to yellow leaves.

In recent years, the phenomenon of watermelon continuous cropping is more serious, which is easy to cause element deficiency. Watermelon common lack of potassium, calcium, boron and iron will cause different degrees of leaf yellowing. Prevention and control methods, first, try not to continuous cropping; Second, for continuous cropping watermelon, while using nitrogen, phosphorus and potassium fertilizer, appropriate mineral fertilizer should be used to supplement the deficiency of medium and trace elements; Third, the watermelon seedlings with deficiency disease can be sprayed with foliar fertilizer in time to effectively prevent the watermelon from deficiency disease.