(1) Symptoms:
Pepper viral diseases can manifest in a variety of ways due to the large number of viruses that affect this crop. There are four main symptom types:
1. Mosaic Type: In the early stages, the veins show slight chlorosis, and dark and light patterns appear on the leaves. The plants do not exhibit obvious stunting, leaf drop, or leaf deformation. However, in severe cases, the veins may shrink, causing uneven foliage and slow growth. The plants become shorter, and the pepper fruits become thin, irregular in color, and less rigid. They also struggle to turn red.
2. Yellowing Type: Infected plants begin to show yellowing starting from the young, tender leaves. This is often followed by excessive leaf drop, flower fall, and fruit loss.
3. Necrosis Type: Parts of the plant tissue die off, resulting in symptoms such as spots, streaks, necrotic mottling, and ring spots. These conditions can lead to severe defoliation, fruit drop, or even complete wilting of the plant.
4. Deformity Type: The plant shows distorted growth, with shortened internodes, stunted development, thickened branches and leaves, and smaller or linear-shaped leaves. The affected fruits may be yellow-green, irregular, and prone to falling off.
(2) Disease Occurrence Conditions:
The host range of cucumber mosaic virus is very broad, primarily overwintering on perennial weeds and in protected fields. It is transmitted by aphids in the following year. The tobacco mosaic virus survives winter in contaminated soil, infected plant debris, seeds, and tobacco products. It spreads mainly through sap contact during sowing, seedling care, planting, and pruning. The occurrence of viral diseases is closely linked to environmental conditions and agricultural practices. High temperatures, drought, and intense sunlight promote aphid population growth, which weakens pepper plants, reduces their resistance, and leads to more severe viral infections. Overuse of nitrogen fertilizers, overly lush plant growth, poor soil conditions like low-lying, compacted, or clayey soils, and late planting of spring peppers all contribute to more severe disease outbreaks. Additionally, growing peppers near solanaceous crops increases the risk of infection.
(3) Control Methods:
1. Selecting Resistant Varieties: Choose disease-resistant varieties based on local growing conditions. Generally, varieties with slender leaves and horn-shaped or bell-shaped fruits are preferred. Sweet peppers with larger, wider fruits are more resistant to antiviral diseases. Heat-tolerant varieties tend to be more resistant than cold-tolerant ones. Some recommended disease-resistant bell pepper varieties include Nongda 22, Agricultural Fat Pepper, Nongle Sweet Pepper, Zhongjiao No. 5, and Sweet No. 6.
2. Seed Disinfection: Soak seeds in a 10% sodium phosphate solution for 20 minutes, then rinse thoroughly with water before germinating or sowing. This helps eliminate viruses that may be present in the seeds. Alternatively, dry heat treatment at 70°C for three days can also be used for fully dried seeds.
3. Strengthen Cultivation Management: Sow at the right time, grow strong seedlings, and implement a crop rotation of more than two years. Apply well-decomposed organic fertilizer and use plastic film covering technology to increase temperature and humidity, promoting early and vigorous growth of pepper plants. Enhance disease resistance by using shade nets to protect against high temperatures and strong sunlight. Intercropping with tall crops like corn, cowpeas, kidney beans, or melons can also help reduce heat stress and sun exposure.
4. Timely Control of Aphids: Monitoring and controlling aphid populations is crucial to prevent the spread of viral diseases.
5. Chemical Control: Apply fungicides such as 20% Virus A WP diluted at 500 times, 50% Bacterin Clear Water diluted at 300 times, Neomycin at 2,000 times, or 1.5% Phytoalexin at 1,000 times. Alternate between these treatments every 7–10 days, applying them 3–4 times in total for effective control.
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