What to Do When Bitter Melon Gets Phytophthora Blight? A Detailed Guide to the Latest Control Methods
Bitter melon Phytophthora blight damages stems, leaves and fruits, occurring more often at the base of the vines and at the nodes of tender vines. The pathogen is Phytophthora parasitica, a fungus of the subphylum Mastigomycotina. In the north it occurs more on autumn cucumbers, while in central and southern China it is more common on spring cucumbers. Besides cucumbers, it also damages winter melon, chieh-qua, zucchini, snake melon, pumpkin, watermelon and other crops. Now let us take a look at the control methods for bitter melon Phytophthora blight!
Damage Symptoms
Bitter melon Phytophthora blight mostly shows symptoms before flowering, and both stems and vines and fruits can be infected. Infected leaves first lose their gloss; initially there are dark green water-soaked lesions, irregular in shape with indistinct edges. When humidity is high, a very thin layer of white mold can be seen growing on the diseased area; when dry, it turns bluish-white and breaks easily. The leaf stalks and vine nodes develop dark green water-soaked soft rot, and the affected parts tend to constrict. When the fruit is affected, dark green sunken lesions appear; under high humidity the fruit quickly softens and rots, sparse white mold grows on the affected part, and the rot gives off a foul odor.
Disease Pattern
The pathogen mainly overwinters in the soil as mycelium, oospores or chlamydospores with diseased plant residues, and seeds can also carry the pathogen. The temperature range for pathogen development is 5-37°C, with the optimum at 28-30°C. Within the suitable temperature range, the length of the rainy season and the amount of rainfall are the decisive factors for the occurrence and epidemic of the disease. If the rainy season comes early, rainy days last long, and rainfall is heavy, the disease occurs early and is severe. In addition, poor field drainage and high soil moisture easily induce Phytophthora blight.
Agricultural Control
For agricultural control of bitter melon Phytophthora blight, a crop rotation of more than 3 years can be implemented, and plastic film mulching with high ridges (beds) can be used to reduce splashing of the pathogen by surface water. Irrigate reasonably and control field humidity. During the rainy season, appropriately reduce watering, and drain water promptly after rain so that the ground dries after the rain. During drought, water promptly; when watering, never flood-irrigate, and do it in the afternoon or evening on a sunny day. Apply more organic fertilizer to promote robust plant growth with deep roots and lush leaves and improve resistance. Adjust the plants promptly to prevent overly dense growth and poor ventilation and light penetration. Remove diseased leaves at any time and burn them.
Chemical Control
For chemical control of bitter melon Phytophthora blight, choose 25% Ridomil wettable powder at 800-1000 times dilution, 80% zineb wettable powder at 600-800 times dilution, 64% Sandofan wettable powder at 500-600 times dilution, 40% fosetyl-aluminum wettable powder at 300-400 times dilution, 80% Xinwansheng wettable powder at 500-600 times dilution, 72.2% Previcur aqueous solution at 400-600 times dilution, 50% potassium copper phosphonate wettable powder at 600 times dilution and other agents, and spray them alternately every 5-10 days for 3-4 consecutive times. Spraying must be thorough and meticulous, covering all leaves, fruits and the nearby ground.