(1) Symptoms:
The disease can affect the plant throughout its entire growth period, with stems, leaves, and fruits all being susceptible. It is most vulnerable before and after budding. At the seedling stage, the stems show water-soaked soft rot, causing the upper part of the plant to collapse. The 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 infected areas, leading to complete wilting and death of the seedlings. In adult plants, the lesions are brown, 3 to 5 cm long, and can encircle the stem within a week. These lesions are usually located at the junctions, slightly sunken or constricted, which causes the whole plant to wilt and die. Stems often show dark green, water-stained lesions near the ground or at the branching points. Under high humidity, a white moldy layer appears, followed by dark brown, contracted lesions that cause the affected stems and leaves to wither and die. Leaf infections result in 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. When dry, the lesions turn light brown. Fruit infections typically begin at the fruit's pedicle or tip, showing dark green, water-soaked lesions. High humidity leads to dense white mold covering the infected fruit. The disease can cause the fruit to drop, or it may dry out, turning dark green and remaining stiff on the branch.
(2) Disease Conditions:
This is a fungal disease caused by *Phytophthora capsici*. The oospores and chlamydospores can survive for 2 to 3 years in infected plants, soil, or seeds. When conditions are favorable, these spores germinate into zoospores, which spread via wind, rain, and agricultural tools, invading roots, stems, or leaves near the ground. Wounded plants are more susceptible to infection. *Phytophthora capsicola* tends to occur in outbreaks, especially in low-lying, waterlogged areas with heavy clay soils, poor drainage, or moisture from dripping in greenhouses. The disease spreads fastest at temperatures between 27°C and 30°C, completing one generation in 2 to 3 days and causing widespread infection in 3 to 5 days. This makes it a highly destructive disease with a short incubation period and high prevalence. In Guangdong, April is typically warm and rainy, creating ideal conditions for severe outbreaks when humidity is high or after heavy rainfall.
(3) Control Methods:
1. Select disease-resistant varieties. Many research institutions have developed resistant varieties such as Chiyou 4, Chaoyou 9, Yuejiao No. 3, and Xiangyan No. 1. Choose and plant these varieties based on local growing conditions and alternate them in different regions. Peppers are generally more resistant than sweet peppers.
2. Seed disinfection. Soak pre-sown seeds in 55°C warm water for 15 minutes, or in 1% copper sulfate solution for 5 minutes, or in 72% Precoq (R) water solution diluted 600 times for 15 minutes. Afterward, rinse and sow or pre-germinate.
3. Practice crop rotation. Avoid planting solanaceous crops in the same area for 2 to 3 years. It’s 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 accelerate seedling growth. Apply fertilizers timely, and add organic manure to clay soils to improve soil structure and drainage. Combine nitrogen, phosphorus, and potassium fertilizers during topdressing. Regular field inspections are essential, and any diseased plants should be removed immediately, taken out of the field, and burned or buried deeply. Do not leave them in ditches or drains. Sprinkle lime powder on the holes to disinfect.
5. Chemical control. For prevention, spray in the afternoon when there is no rain, especially when air and soil humidity is high or at the early stage of the disease. Options include 75% Rhizoctonia WP diluted 600 times, 75% Mancozeb WP diluted 600 times, 0.3% copper sulfate solution, 77% Mancozeb WP diluted 800 times, 36% Drench Buster suspension diluted 600 times, 70% Diflubenzuron wettable powder diluted 600 times, or a 1:1:200 Bordeaux mixture. Rotate these treatments every 5 to 7 days and apply continuously for 2 to 3 rounds.
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