What are the symptoms of bitter melon Phytophthora blight? What are the prevention and control methods?
Bitter melon is a vegetable with a distinctive bitter taste. Although it tastes bitter, it has the effect of clearing heat and detoxifying, so it is a vegetable very suitable for eating in summer. During the cultivation of bitter melon, bitter melon Phytophthora blight is very likely to appear due to improper management and other reasons. So what symptoms does this disease have? What are the prevention and control methods?
1. What symptoms does bitter melon Phytophthora blight have?
Bitter melon Phytophthora blight damages stems, leaves and fruits. This disease occurs more often at the base of the vines and at the nodes of tender vines. At first it appears dark green and water-soaked, then turns light brown, constricts and becomes thinner. The leaves above the diseased part wilt and die, while the leaf color remains green; leaf infection mostly starts from the leaf margin or leaf tip. The lesions are dark green, round or irregular, water-soaked, with indistinct edges and faint concentric rings. When moist, they expand rapidly and become soft rot; when dry, the lesions stop developing, with brown edges and a greenish-white center, drying up and easily breaking. On the fruit, dark green, nearly round, water-soaked lesions appear, with no obvious edges, quickly spreading to the entire fruit surface, shrinking, becoming soft rot, and producing a sparse grayish-white moldy growth on the surface (sporangia and sporangiophores).
2. Transmission routes and disease occurrence conditions
The pathogen overwinters in the soil as mycelium and oospores with diseased residue tissues. In the second year, the mycelium or oospores produce sporangia and zoospores upon contact with water, spread to melons through irrigation water and rainwater, germinate germ tubes, produce appressoria and penetration hyphae that penetrate the epidermis and enter the host. Under high temperature and high humidity conditions, lesions appear in 2 to 3 days, producing large numbers of sporangia on them, which spread and multiply through wind, rain or irrigation water, causing repeated infections many times.
The pathogen produces sporangia in two ways: first, hyphae emerge from the stomata, branch, and produce hypha-like sporangiophores on the branches, with sporangia formed at the tips; second, shorter hypha-like sporangiophores emerge from the stomata, with sporangia formed at the tips. After 48, 72 and 96 hours, the average number of sporangia produced on both sides of each 1 square cm of leaf was 24.2, 95.3 and 254.8 respectively. After inoculation, the sporangia release zoospores that rest on the leaf surface for 2 hours before germinating, or the sporangia germinate directly to produce germ tubes and begin to invade through the gaps between the guard cells of the stomata. The hyphae spread between and within the leaf cells, and hyphae may also emerge from the stomata, then invade again through the stomata or spread on the leaf surface. After several days of incubation, symptoms appear. The severity of melon Phytophthora blight is related to how early or late the rainy season arrives that year, the number of rainy days, the amount of rainfall and the temperature. In years when the disease starts early and the temperature is high, the disease is severe. Generally, the disease begins when the rainy season starts, and spreads rapidly or causes an epidemic when there are heavy rainstorms. In production, continuous cropping with cucurbit crops and flat-bed cultivation make the disease likely to occur, and long-term flood irrigation, frequent watering and large water volumes make the disease severe.
3. What are the prevention and control methods for bitter melon Phytophthora blight?
1. Use plastic film mulching and high-ridge (bed) cultivation to reduce splashing of pathogens from the ground. Irrigate reasonably and control field humidity. During the rainy season, appropriately control watering, drain water promptly after rain, and ensure the ground dries after rain. In case of drought, water promptly; when watering, never use flood irrigation, and do it in the afternoon or evening of a sunny day. Apply more organic fertilizer to promote robust plant growth, deep roots and lush leaves, and improve resistance. Adjust the plants promptly to prevent excessively dense growth and poor ventilation and light penetration. Remove diseased leaves at any time and burn them.
2. Apply chemical control promptly in the early stage of the disease. Choose 25% Ridomil wettable powder 800-1000 times solution, 80% zineb wettable powder 600-800 times solution, 64% Sandofan wettable powder 500-600 times solution, 40% fosetyl-aluminum wettable powder 300-400 times solution, 80% Xinwansheng wettable powder 500-600 times solution, 72.2% Previcur water agent 400-600 times solution, 50% potassium copper sulfate wettable powder 600 and other agents, and spray them alternately, once every 5-10 days, for 3-4 consecutive times. Spraying should be thorough and meticulous, covering all leaves, fruits and the nearby ground.