Watermelon fruit spot disease prevention and treatment
Recently, a watermelon fruit spot disease was reported in Funan County, Hebei Province. This disease is classified as a national plant quarantine pest and is caused by a bacterial pathogen. It not only affects watermelons but can also infect other cucurbit crops such as melons, pumpkins, cucumbers, and zucchini. To effectively manage this disease, the following preventive measures are recommended:
1. Selecting disease-resistant varieties is one of the most effective strategies. Different watermelon cultivars show varying levels of susceptibility. In areas where the disease is prevalent, it's advisable to replace susceptible varieties with resistant ones. For example, triploid varieties tend to be more resistant than diploid types. Dark green varieties usually have lower resistance compared to lighter green or red-skinned types. The new Hongbao variety, for instance, shows higher resistance to the disease.
2. Seed treatment plays a crucial role in reducing the risk of infection. Before sowing, seeds should be soaked in a mixture of juice and pulp for 24 to 48 hours. After washing, they should be immersed in 1% hydrochloric acid for 5 minutes or 1% calcium hypochlorite for 15 minutes. Rinse thoroughly with clean water and dry before planting. Additionally, soaking seeds in 1% potassium permanganate solution for 20 minutes, followed by rinsing with fresh water for 20 minutes, can further reduce the chance of bacterial contamination.
3. Crop rotation is an essential practice that helps break the disease cycle. The longer the crop rotation period, the better the control effect. It's important to avoid continuous cropping in fields where fruit spot disease has been observed, as this can lead to a buildup of pathogens in the soil.
4. Field management is critical in preventing the spread of the disease. During autumn, deep plowing can help bury diseased plant debris, wild hosts, and bacteria in the soil, thereby reducing their population. When preparing the planting area, create a 30 cm wide and 40 cm deep trench at the base of each planting hole. Line the bottom of the trench with 15-20 cm of straw, cover it with soil, and increase the root zone’s breathing capacity to improve plant health. Remove all diseased fruits, weeds, and wild host plants, especially those from the cucurbit family. Disinfect tools and equipment to prevent cross-contamination. Use drip irrigation or hose systems instead of overhead sprinklers to minimize the spread of bacteria through water droplets.
5. Chemical control is necessary when the disease is detected. Early application of antibiotics such as streptomycin or tetracycline is recommended. Spraying should be done every 7–10 days depending on weather conditions and disease severity. In heavily infested areas or during the rainy season, it's advised to start spraying before symptoms appear. Options include 30% basic copper sulfate suspension diluted 400–500 times, 47% mancozeb wettable powder diluted 800 times, 56% copper hydroxide dispersible granules diluted 600–800 times, 50% diclofenac copper (DT) fungicide diluted 500 times, 77% copper oxychloride wettable powder diluted 500 times, and 30% copper oxychloride suspension diluted 800 times. Apply approximately 60 liters of spray per acre, repeating every 10 days as needed.
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