Disease Prevention Late Blight Late blight is a widespread and severe disease affecting potatoes across the country. In areas where resistant varieties are not used, yield losses can reach 20% to 50%, with some cases showing up to 30% weight loss. The disease also affects tomatoes, green peppers, and eggplants. When plants are infected, small brown spots appear on the leaf edges or tips, surrounded by yellow-green lesions. High humidity, especially in the morning or during rain, causes rapid expansion of these lesions, leading to blueish discoloration, drying, and white mold growth on the leaf surface. The white mold consists of conidia, with sporangia shaped like peaches. Spores can infect tubers, causing brown spots on the skin and internal tissue decay. Before soft rot sets in, the affected area becomes hard, and the potato flesh turns rust-brown when cut. Once soft rot pathogens enter, the tuber begins to rot. Transmission Pathways and Conditions The spores of late blight are very small and can enter through stomata or the epidermis of tubers. Wet leaves from morning dew or rain create favorable conditions for infection. The optimal temperature for pathogen development is 24°C, with a maximum of 30°C and a minimum of 10°C. Zoospore growth thrives between 12–13°C, with a maximum of 25°C and a minimum of 2°C. Hyphae can survive in tubers over winter, and soil is often contaminated. Diseased tubers are the main source of infection, spreading to healthy plants under suitable conditions. Rain can carry spores to tubers, and mechanical damage during harvest can introduce pathogens. Spores on soil, stems, and leaves can also invade tubers. Control Methods 1. Use disease-resistant varieties.
2. Remove diseased potatoes before planting.
3. Apply chemical treatments: For early detection, spray 25% Rhodoxima WP at 800 times dilution. Repeat every 10 days for 2-3 applications. Follow with Bordeaux mixture (500g copper sulfate, 500g quicklime in 50L water) for effective control.
4. Improve soil drainage to reduce spore entry into tubers.
5. Remove and destroy infected plants early, especially in dense plantings, to prevent spore spread and future infections. Ring Rot Ring rot primarily affects the vascular bundles of plants and tubers, causing internal tissue decay. Infected plants grow slowly, with symptoms appearing before and after flowering, including partial wilting. Leaves turn yellow from the edges and curl inward, and branches die gradually. In tubers, the pathogen enters via stolons, causing brownish-red rot. Pressing the tuber separates the flesh from the cortex, but the bud eyes remain unaffected, distinguishing it from bacterial wilt. Transmission and Conditions Seedborne transmission is the primary route, especially through infected cutting tools. Contaminated tools like baskets or implements can also spread the disease. Soil is not a major transmission route. Optimal temperature for ring rot is 20–23°C, with field temperatures around 18–20°C. Temperatures above 31°C inhibit disease development. Control Measures 1. Plant virus-free seedlings and produce certified seed potatoes.
2. Remove diseased tubers before planting, and sterilize cutting tools with alcohol or flame.
3. Use resistant varieties.
4. Avoid planting seeds from infected plots to prevent disease spread. Bacterial Wilt Bacterial wilt causes sudden wilting of stems or branches, while other parts of the plant remain healthy. The bacteria invade the vascular system, first affecting one stem, then spreading throughout the plant. Tubers become discolored from the umbilical area, and pressing them releases a milky fluid. Unlike ring rot, the flesh and cortex do not separate. Severe cases lead to complete rot and failure to germinate. Transmission and Disease Mechanism Bacterial wilt spreads through infected tubers, parasitic plants, and contaminated soil. Cutting tools and agricultural equipment can transfer the pathogen. The disease is most active at 30°C, and high humidity and warm temperatures accelerate its spread. Bacteria can survive in soil for over 14 months. They thrive in slightly acidic conditions (pH 6–8), with an optimal concentration of 251.2 nanomoles/liter (pH 6.6). Control Strategies 1. Use resistant varieties, as no fully immune ones exist.
2. Plant virus-free seed potatoes, especially in southern regions where the disease is prevalent.
3. Practice crop rotation, avoid weeding, and minimize root damage to reduce transmission.
4. Prohibit planting from infected sources to prevent further spread. Viral Diseases Several viruses affect potatoes, including X, A, S, M, Y, and Roll Leaf viruses. Each has distinct symptoms and transmission methods. Symptoms and Transmission Routes - X Virus: Causes mosaic patterns on leaves, reducing yields by up to 50%. Spread through contact.
- A Virus: Leads to mottled leaves and reduced yield, transmitted by aphids.
- S Virus: Causes curled, wrinkled leaves and smaller tubers.
- M Virus: Results in leaf curling and deformation.
- Y Virus: Causes severe necrosis and leaf drop, reducing yield by 80%.
- Roll Leaf Virus: Causes leaf curling and tuber necrosis, spread by locusts.
- Spindle Tuber Viroids: Causes spindle-shaped tubers and reduced yield. Control Methods 1. Produce virus-free seedlings using shoot tip cultures.
2. Screen and propagate virus-free plants.
3. Implement local measures to prevent insect and mechanical transmission.
4. Use uniform, high-quality seed tubers with minimal economic loss. Black Stem Disease Black stem disease is common in northern and northwestern regions, with incidence ranging from 2% to 50%. Diseased tubers rot before planting, and seedlings may be pulled out, leading to empty shoots. Symptoms Infected plants grow shorter than healthy ones, with hardened stems, shortened internodes, yellowing and curling leaves, and eventual death due to base rot. Affected plants are easily pulled out because of blackened stem bases. Transmission and Conditions Spread mainly through infected seed tubers, and can occur via cutting tools or lenticels. High moisture and temperature increase disease risk. Bacteria thrive between 15–25°C, with optimal development at 23–27°C. Control Measures 1. Establish disease-free seed production areas.
2. Inspect and remove diseased tubers before planting.
3. Choose well-drained land to prevent water accumulation.
4. Chemical treatment: Soak tubers in 0.01–0.05% propylene glycol, 0.05–0.1% kasugamycin, or 0.2% potassium permanganate for 15–30 minutes.
5. Dry tubers before storage and ensure proper ventilation to avoid moisture buildup. Xuzhou Xinbaisheng Protective Equipnent Co., Ltd. , https://www.xinparkson.com