How to prevent and control watermelon leaf blight? A detailed guide to the latest methods
Leaf blight is one of the common diseases of watermelon, occurring mostly on open-field watermelons in summer and autumn, and spring-crop watermelons can also be affected, with a general incidence rate of 10-30%, and diseased plant rates of over 80% in severely affected plots, causing large numbers of leaves to wither and die, significantly affecting watermelon production. Besides harming watermelon, it also harms melon, cucumber, winter melon, pumpkin and other cucurbit plants. Let's take a look at the prevention and control methods for watermelon leaf blight!
Damage characteristics
Watermelon leaf blight mainly harms the leaves, and can also harm the stems and vines and the fruit. When cotyledons of seedlings are affected, it mostly occurs at the leaf margins, initially as small water-soaked spots, which later expand into brown water-soaked, round or semicircular spots. Under high humidity conditions, it can affect the entire cotyledon, causing it to wither. When true leaves are affected, it mostly occurs at the leaf margins or between the veins, initially as small water-soaked spots, which under high humidity rapidly merge and seep through, causing the leaves to lose water and wilt green. In hot, dry weather, round brown spots 2-3 mm in diameter form; when the weather is humid, they can merge into large brown spots, the lesions become thinner, and in severe cases cause leaf blight. When stems and vines are affected, slightly sunken light brown oval or spindle-shaped spots are produced. When the fruit is affected, round sunken dark brown spots with slightly raised edges are produced, and in severe cases cause the fruit to rot.
Occurrence pattern
The pathogen of watermelon leaf blight has no strict temperature requirements; disease can occur at temperatures of 14-36°C and relative humidity above 80%. In fields with many rainy days and large rainfall amounts, and relative humidity above 90%, it is prone to becoming epidemic or breaking out on a large scale. Wind and rain facilitate the spread of the pathogen, causing the disease to occur widely. In continuous cropping fields, fields with one-sided or heavy application of nitrogen fertilizer, and poor soil, the plants have weak disease resistance and the disease is severe. Continuous sunny days and long sunshine hours have an inhibitory effect on the disease. Disease resistance varies among varieties; Jinzhong and Guannong are relatively susceptible. In recent years it has shown a trend of becoming increasingly serious, and attention should be paid to it in production.
Prevention and control methods
1. Establish disease-free seed production fields and select disease-tolerant varieties suitable for local cultivation. Currently, the more disease-resistant varieties include Zhengzhou No. 5, Zhengza No. 7, Xinong No. 8, Yueyou No. 2, Fuzhou Watermelon, Xin Hong Bao, etc.
2. After the watermelon harvest, take care to remove diseased residues, bury them deep in a centralized place or burn them, and do not pile diseased residues at the edge of the field.
3. Adopt a formula fertilization technique, apply compost fermented with enzyme bacteria, avoid one-sided or excessive application of nitrogen fertilizer, and begin spraying Huimanfeng liquid fertilizer before fruit setting, at 320 milliliters per mu diluted 500 times with water, to improve disease resistance.
4. Scientifically determine the sowing date. For open-field cultivation, it is advisable to sow when the average daily temperature is stable above 15°C and the soil temperature at a depth of 5 cm is stable above 12°C. If you want to sow early, plastic film mulching can be used to reach the above temperatures before sowing.
5. For seeds that may carry the pathogen, soak the seeds in a 1000-fold dilution of 75% chlorothalonil wettable powder or 50% iprodione wettable powder for 2 hours, rinse clean, then germinate and sow.
6. Where conditions permit, advocate the use of rain-shelter cultivation. For open-field watermelon, special attention should be paid after rain to opening furrows for drainage to prevent moisture retention, which plays an important role in reducing the disease.
7. Adopt the trellis cultivation method, with 1500 plants per mu, using single-vine pruning, removing the first female flower when there are 6-7 leaves, and retaining 12-13 leaves. This not only increases yield and income but can also reduce the disease.
8. Before the disease occurs, when no lesions are yet visible, begin spraying 50% procymidone wettable powder at 1500-fold dilution, or 50% iprodione wettable powder at 1000-fold dilution, 75% chlorothalonil wettable powder at 600-fold dilution, 70% mancozeb wettable powder or dry suspension powder at 500-fold dilution, or 80% Daconil wettable powder at 600-fold dilution, all of which are effective. Spray 60 liters of the prepared solution per mu, once every 7-10 days, for 3-4 consecutive treatments.