(1) Symptoms typically appear after the initial onset of the disease. The disease course is prolonged, and leaf wilting occurs during the day but may recover at night or on cloudy days. After a few days, yellowing begins from the lower leaves and gradually moves upward, leading to stunted growth. There are two main scenarios: First, grafted seedlings show dark brown water-soaked lesions near the ground level on the stem, which eventually rot and cause the entire plant to die. Second, there are no visible signs of water-soaking or decay at the stem base, and the vascular tissues of pumpkins and cucumbers remain unaffected. When digging up the roots, fine roots appear brown and rotten. Some main and lateral roots also turn light brown to dark brown. In severe cases, all roots become dark brown, and the fine root tips split longitudinally. Within these cracks, gray and black fungal mycelium can be observed, and dense black spots are visible in the root cortex cells.
(2) The causal agent is *Phytophthora* spp., a type of oomycete fungus. The optimal temperature for pathogen development is between 24–28°C, with a maximum of 32°C and a minimum of 8°C. Interestingly, lower temperatures often promote the growth and development of the pathogen, making it more active under cooler conditions.
(3) Prevention and control measures include:
1. Proper disinfection of seedbeds. Treating the soil at 50°C for 10 minutes significantly reduces disease incidence. Products such as Green Earthworm No. 1 (containing Stachybotryol and Hymexazol) can also be used for soil treatment.
2. Apply biological fertilizers to the soil. These help improve soil health and suppress pathogenic activity.
3. Use disease-resistant rootstocks, such as Yunnan Black-Skinned Pumpkin and Liaowu No. 1.
4. Early application of 50% Benomyl WP diluted 1500 times, applied by root irrigation. Each plant should receive about 250 ml of the solution to ensure effective control.
These methods, when combined, offer a comprehensive approach to managing this disease and reducing crop losses.
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