(1) Symptoms:
This disease can affect the plant throughout its entire growth cycle, with stems, leaves, and fruits all being susceptible. The plant is most vulnerable just before and after budding. During the seedling stage, the stems show water-soaked soft rot, causing the upper parts to collapse. Lesions appear dark green and later develop into large, spindle-shaped spots. When humidity is high, a white, sparse moldy layer may form on the affected areas, leading to wilting and death of the entire seedling. In adult plants, lesions are brown in color and can grow up to 3–5 cm long, encircling the stem within a week. These lesions are often found at the junctions, slightly sunken or constricted, which leads to the whole plant wilting and dying. The stems are commonly affected at ground level and at branching points, starting with dark green, water-stained lesions. High humidity promotes the formation of a white mold layer, which eventually turns into a contracted, dark brown area, causing the affected stems and leaves to wither and die.
Leaf symptoms include round or nearly circular lesions, about 2–3 cm in diameter, with a dark brown center and yellow-green edges. As the disease progresses, the leaves become soft and rotten. Under dry conditions, the lesions turn light brown. On the fruit, the disease typically begins at the pedicel or tip, showing a dark green, water-soaked lesion. When humidity is high, the infected fruit develops a dense white mold layer. The fruit may either fall off or dry out, turning dark green and stiff while remaining attached to the branch.
(2) Disease Conditions:
The disease is caused by the fungus *Phytophthora capsici*. Oospores and chlamydospores can survive for 2–3 years in diseased plants, soil, or seeds. When conditions are favorable, these spores germinate into zoospores, which spread through wind, rain, and agricultural tools, invading roots, stems, leaves, or fruits near the ground. Wounds on the plant make it easier for the pathogen to enter. The disease shows distinct epidemic patterns in the field, often appearing in low-lying, waterlogged areas with heavy clay soils, poor drainage, or moisture buildup under sheds. At temperatures between 27–30°C, the disease spreads rapidly—reaching one generation in 2–3 days and causing widespread infection in 3–5 days. This makes it a highly destructive disease with a short onset cycle and high prevalence. In Guangdong, April is usually warm and rainy, with high humidity, making it a peak period for severe outbreaks.
(3) Control Methods:
1. Choose disease-resistant varieties. Many research institutes have developed resistant varieties such as Chiyou 4, Chaoyou 9, Yuejiao No. 3, and Xiangyan No. Depending on local planting practices, these varieties should be selected and rotated to reduce disease pressure. Generally, peppers are more resistant to this disease than sweet peppers.
2. Seed disinfection. Soak pre-sprouted seeds in 55°C warm water for 15 minutes, or in a 1% copper sulfate solution for 5 minutes, or in a 72% Precoq (R) solution diluted 600 times for 15 minutes. After washing, the seeds can be sown or primed.
3. Practice crop rotation. Avoid planting solanaceous crops in the same plot for 2–3 years. It is best to rotate with onions, garlic, beans, melons, or rice crops every three years.
4. Cultivation management. Use deep trenches to drain water promptly and avoid waterlogging. Promote mulching to increase soil temperature and speed up seedling growth. Apply fertilizers timely, especially organic manure in clay soils to improve drainage and permeability. Combine nitrogen, phosphorus, and potassium fertilizers during topdressing. Regular field inspections are essential to detect and remove diseased plants immediately, burning or burying them deeply to prevent further spread. Do not leave them in ditches or drains. After removal, sprinkle lime powder on the holes to disinfect.
5. Chemical control. For prevention, spray when air and soil humidity is high, during dry afternoons. Options include 75% Rhizoctonia WP diluted 600 times, 75% WP 600 times, 0.3% copper sulfate solution, 77% Mancozeb WP 800 times, 36% Dew Buster suspension 600 times, 70% Dexamethasone wettable powder 600 times, or a 1:1:200 Bordeaux mixture. Rotate these products every 5–7 days and apply continuously for 2–3 times to effectively manage the disease.
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