(1) Symptoms typically appear after the initial onset of the disease. The disease progresses slowly, and leaf wilting occurs during the day but often recovers at night or on overcast days. Over several days, the lower leaves begin to yellow and gradually move upward, leading to stunted growth. There are two distinct scenarios: First, grafted seedlings show symptoms where the stem near the soil line becomes water-soaked, turning brown and rotting, eventually causing the entire plant to die. Second, in some cases, the stem base does not show water-soaked or rotten areas, and the vascular bundles of pumpkins and cucumbers remain unaffected. However, when roots are examined, fine roots appear brown and decayed. Some main and lateral roots also show light to dark brown discoloration. In severe cases, all roots turn brown or dark brown, and the fine root tips split longitudinally. Within these cracks, gray and black fungal mycelium may be visible, and dense black spots can be observed inside the root cortex cells.
(2) The pathogen responsible is *Phytophthora* spp., a type of fungus belonging to the subgenus *Phytophthora*. The optimal temperature range for pathogen development is 24–28°C, with a maximum of 32°C and a minimum of 8°C. Generally, lower temperatures are more favorable for the growth and spread of the pathogen.
(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 Stachybotrys sp. and Hymexazol) can also be used for soil treatment. 2. Applying biological fertilizers to the soil to improve overall plant health and resistance. 3. Using disease-resistant rootstocks like Yunnan Black-Skinned Pumpkin and Liaowu No. 1. 4. Early application of 50% Benomyl WP diluted 1500 times for root irrigation, with each dose being approximately 250 ml of solution per plant. These measures help manage the disease effectively and reduce long-term damage to crops.
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