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 bacteria. It can affect not only watermelons but also other cucurbit crops such as melons, pumpkins, cucumbers, and zucchini. To effectively manage this disease, the following preventive measures are recommended:
1. Choosing disease-resistant varieties is one of the most effective strategies. Different watermelon cultivars show varying levels of susceptibility. In areas where the disease is severe, it's advisable to replace susceptible varieties with more resistant ones. For example, triploid watermelons tend to be more resistant than diploids, and certain varieties like the new Hongbao have shown higher resistance compared to others.
2. Seed treatment plays a crucial role in reducing bacterial infection. Before sowing, seeds should be fermented in juice and pulp for 24–48 hours. After washing, they should be soaked in 1% hydrochloric acid for 5 minutes or in 1% calcium hypochlorite for 15 minutes. Rinse thoroughly with clean water and dry them before planting. Additionally, soaking seeds in 1% potassium permanganate solution for 20 minutes, followed by rinsing and drying, can further reduce the risk of bacterial contamination.
3. Crop rotation is a simple yet highly effective method to control many pests and diseases. The longer the crop rotation period, the better the disease suppression. Avoid continuous planting in fields where fruit spot disease has occurred previously. This helps break the life cycle of the pathogen and reduces its buildup in the soil.
4. Field management is essential for preventing disease spread. Deep plowing during autumn can bury diseased plant residues, wild hosts, and bacteria deep into the soil, thereby reducing their survival. It’s also important to remove weeds and other host plants, especially those from the cucurbit family. When preparing the field, dig a 30 cm wide and 40 cm deep trench at the base of each planting hole. Place 15–20 cm of straw at the bottom, cover it with soil, and improve root development and aeration. Ensure all tools are disinfected, and use drip irrigation instead of overhead sprinklers to minimize the spread of pathogens through water droplets.
5. Chemical control is necessary when the disease is already present. Antibiotics such as streptomycin and tetracycline can be used for early-stage spraying. Apply these treatments every 7–10 days depending on weather conditions and disease severity. In heavy-infestation areas, especially before the rainy season begins, consider using products like 30% basic copper sulfate suspension (diluted 400–500 times), 47% mancozeb wettable powder (800 times), 56% oxycarboxin microgranules (600–800 times), 50% dichlofluanid (DT) fungicide (500 times), 77% copper oxychloride wettable powder (500 times), or 30% copper oxychloride suspension (800 times). Spray 60 liters per acre, repeating every 10 days or so to maintain effective protection.
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