What are the latest control methods for powdery mildew on bitter gourd?
Powdery mildew on bitter gourd occurs commonly on bitter gourd plants, and different varieties have different resistance to powdery mildew. It mainly occurs on leaves, followed by petioles and vines. The disease is caused by infection by fungi of the genus Sphaerotheca, which are obligate parasites and can only carry out a parasitic life on living hosts. The main symptom is damage to the leaves. Let us take a look at the control methods for powdery mildew on bitter gourd!
Damage symptoms
First, small round powdery mildew spots appear on the front or back of the lower leaves of the plant, gradually expand and become thick and dense, and soon merge into one patch. In the later stage of the disease, the entire leaf is covered with white powder, then turns grayish white, and finally the entire leaf becomes yellow-brown and dry. The disease mostly starts on the middle and lower leaves, and then gradually spreads to the upper leaves.
Conditions for disease occurrence
The pathogen can survive the winter on cucurbit vegetables and flowers such as Chinese rose in greenhouses, and after overwintering produces conidia, which spread by airflow. It takes about more than 20 hours from spore germination to infection, so the disease develops very quickly and often becomes epidemic in a short period. The pathogen can be active at 10-30°C, with the optimum temperature being 20-25°C. The disease develops quickly at a relative humidity of 45-75%. When it is below 25%, conidia can still germinate and cause disease, while above 95%, the disease is significantly inhibited.
Control methods
1. For the control of powdery mildew on bitter gourd, first implement crop rotation. Do not plant continuously with cucurbit vegetables. Before sowing, apply new high-fat film to the soil surface to prevent soil compaction, isolate sources of disease and insect pests, and increase the emergence rate.
2. Before sowing bitter gourd, soak the seeds in warm water at about 55°C, let them cool naturally, and continue soaking for 12 hours. Before sowing, mix the seeds with new high-fat film to repel underground diseases and insect pests, strengthen respiration intensity, and increase the seed germination rate.
3. Different varieties of bitter gourd have different resistance to powdery mildew. Generally, early-maturing varieties have weak resistance, while mid- and late-maturing varieties have stronger resistance. Attention should be paid to cultivating strong seedlings, reasonable close planting, timely pruning of branches and leaves, improving ventilation and light transmission conditions, making plants grow robustly, and improving disease resistance.
4. Commonly used chemicals for powdery mildew on bitter gourd include 15% triadimefon wettable powder, or 20% triadimefon emulsifiable concentrate at 2000-3000 times dilution, or 50% carbendazim wettable powder at 500 times dilution, or wettable sulfur powder at 300 times dilution, or 75% chlorothalonil wettable powder at 600-800 times dilution.
5. In greenhouses, use chlorothalonil smoke agents for fumigation to control both downy mildew and powdery mildew. When spraying, pay attention to spraying evenly on the middle and lower old leaves and the undersides of leaves. In the early stage of disease occurrence, spray once every 7-10 days for 2-3 consecutive times, which can achieve a relatively good control effect.