Potato Late Blight Prevention and Control Technology

Potato late blight is a highly destructive plant disease that has plagued potato crops for decades. In the 1950s, it caused widespread devastation in parts of China, while in the 1960s, the introduction of resistant varieties significantly reduced its impact. However, as disease resistance in these varieties declined over time, and climate conditions became more favorable, the incidence of late blight began to rise again, particularly in regions with high humidity and frequent rainfall. Symptoms of late blight typically appear on leaves, stems, petioles, and tubers. The disease often starts as water-soaked spots on the leaf margins, which rapidly expand under wet conditions. These lesions lack a clear boundary from healthy tissue and may develop a faint white mold along the edges, especially on the underside of the leaves. In severe cases, the infection spreads to the main veins or petioles, causing the leaves to wilt and eventually turn black, leading to a complete collapse of the plant. When dry, the affected areas become brown and lose their moldy appearance. Infected tubers show irregular, light brown or gray-purple lesions that may be slightly sunken. Beneath the surface, the tissue turns brown and necrotic. These tubers are prone to secondary infections, such as bacterial soft rot, which can cause them to decay in the field or during storage. The stems are rarely directly infected but can become affected if the lesions spread from the petioles. Under humid conditions, white mold may appear on the stem surfaces, and in severe cases, the stems turn brown and die. Phytophthora infestans, the pathogen responsible for late blight, is a highly specialized fungus that primarily infects potatoes and tomatoes. While it can only grow on specific hosts, it has a narrow but significant host range. Studies have shown that only certain strains of P. infestans can infect tomatoes, while most can affect various potato species—except those with high levels of resistance. The disease cycle begins when infected seed potatoes are planted. Many of these seeds either fail to germinate or rot before emergence, but some may grow into healthy plants. A small percentage of these plants may develop subtle stem lesions at the base. In moist environments, these lesions produce sporangia, which serve as the primary source of infection. Wind and rain can carry these spores to nearby plants, initiating new infections. Residual infected tissue in the soil from previous seasons can also act as an initial source of disease, as can contaminated tubers left outside before planting. Late blight thrives in cool, moist conditions. Relative humidity must be above 85% for spore formation, and near saturation (over 90%) is ideal. Sporangia often form in large quantities during the evening. They tend to release when humidity fluctuates, typically falling off by 8 a.m. and peaking at 10 a.m. on sunny days. For germination, a film of moisture on the leaf surface is essential. At temperatures below 13°C, spores germinate and produce swimming cells, which can invade the plant within 3–5 hours. Under favorable conditions, a single infection point can lead to a large lesion in just 3 days, while cooler weather may extend this process to 6–7 days. Control strategies include breeding and promoting resistant potato varieties, establishing disease-free seed production areas, and using chemical treatments. Early detection is crucial. Farmers should monitor fields regularly, especially in high-risk regions, and take action as soon as the first infected plant appears. Removing and burying infected plants, or applying copper sulfate or metsulfuron, can help prevent further spread. Spraying fungicides like 25% propamocarb wettable powder, 58% mancozeb, or Bordeaux mixture at regular intervals (every 7–10 days) is also effective. To reduce the risk of resistance, farmers should rotate fungicides. In areas where resistance to certain chemicals has developed, alternatives like Bayer’s Silverfal can offer better control.

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Jiangxi Chengzhi Bioengineering Co., Ltd , https://www.chengzhi-bio.com