As the rainy season has officially begun, watermelon farmers need to be on high alert. During the summer months, watermelon crops are particularly vulnerable to two serious diseases: epidemic disease and anthracnose. It's crucial for growers to take preventive measures now to avoid significant losses later.
Watermelon epidemic disease, also known as *Phytophthora infestans*, is commonly called “the death bug.†This soil-borne fungal disease can affect both seedlings and mature plants. The disease spreads quickly in hot, wet conditions, especially during the late growth stage of the crop. With early and prolonged rainfall, the disease tends to appear earlier and become more severe, leading to heavy losses. The peak of the disease often coincides with peak rainfall periods. The optimal temperature range for this pathogen is between 5°C and 37°C.
Symptoms of the disease typically start on the leaves, where dark green, water-soaked spots appear—either round or irregular in shape. Under high humidity, these spots may rot and look as if they've been scalded by boiling water. As the disease progresses, the lesions turn light brown and become brittle. On the stems, the infection begins as a spindle-shaped, water-soaked, dark green depression that eventually rots, causing the plant to die. On the fruit, the disease starts as a dark green, water-soaked spot that rapidly expands, leading to rotting, an unpleasant silage-like odor, and the appearance of dense white mycelium on the surface.
To manage the disease, it’s important to act early. Apply 50% mancozeb wettable powder diluted at 700–800 times, or 72.2% mefenoxam at 800 times, or 64% fosetyl-aluminum at 500 times. Spray every 7–10 days, applying up to 3–4 treatments. In severe cases, the same solution can be used to drench the roots, using 0.4–0.5 liters per plant. Combining foliar sprays with root irrigation yields better results.
Watermelon anthracnose is mainly spread through infected seeds. Once the disease takes hold, it can multiply rapidly and spread via rainwater or irrigation, causing secondary infections. Currently, we're seeing a surge in anthracnose cases during the summer. Field observations show that low-lying areas with poor drainage, excessive nitrogen use, and poor air circulation are more prone to outbreaks.
The symptoms begin with small, water-soaked spots on the leaves, often surrounded by a yellow-brown halo. The center of the lesion becomes dark brown and may develop concentric rings. The affected tissue becomes brittle when dry. On mature fruits, the infection appears as water-soaked brown spots, sometimes with cracks. High humidity can lead to rapid rotting.
For control, use 25% prochloraz emulsifiable concentrate at 1000 times dilution or 50% propiconazole wettable powder at 1500 times. Regular spraying is essential to keep the disease under control. Proactive management now can prevent major losses later in the season.
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