Bacterial angular leaf spot

How to prevent and treat bacterial angular spot disease of loofah? Here is a detailed introduction:

(1) Symptoms

It mainly harms leaves and fruits, and occasionally occurs on stems. When the disease occurs in seedlings, round or oval water-soaked sunken lesions appear on the cotyledons, which then turn brown and dry up. When the leaves of mature plants are affected, they initially appear as water-soaked light green spots, which then expand and turn light brown. Due to the restriction of leaf veins, they become polygonal lesions. Later, the lesions become grayish white and easily perforated. When the humidity is high, milky white mucus, i.e. bacterial pus, is produced on the lesions. The lesions on stems, petioles, and melons are initially water-soaked and nearly circular, and then become light gray. Cracks often appear in the middle of the lesions, and bacterial pus appears in the diseased parts when it is humid. The lesions on the fruit often expand inwards, and the fruit rots in the later stage and has a bad smell. Young fruits are affected and easily rot and fall early.

(2) Conditions for disease onset

Bacterial angular leaf spot is a bacterial disease caused by infection by bacteria of the genus Pseudomonas. The pathogen overwinters in the seeds or in the soil with the remains of the diseased plants, and can survive on the seeds for 2 years. When the seeds germinate, the attached pathogen infects the cotyledons. After the pathogen overwinters in the soil, it is infected by rainwater or irrigation water splashing onto the stems, leaves or fruits. The pus on the lesions is spread through rainwater, insects, agricultural operations, etc., and the pathogen invades through stomata, water holes and wounds.

The disease is most likely to occur at temperatures between 18 and 25 degrees Celsius and relative humidity above 75%. The disease is more likely to occur in areas with heavy rainfall, high humidity, low-lying terrain, improper management, and repeated cropping for many years. The disease is more likely to occur in areas with poor ventilation, high humidity, and long condensation time in protected areas.

(3) Prevention and control methods

① Different varieties have different disease resistance.

② Leave seeds in disease-free fields or disease-free plants to prevent seeds from being infected with bacteria. Before germination and sowing, seeds should be treated to eliminate bacteria. Common methods include:

Soak seeds in warm water: Soak seeds in 50℃ warm water for 20 minutes.

Seed soaking with chemicals: soak the seeds in 200×10-6 concentration of phytocomycin for 1 hour, then take out, wash and germinate; or soak the seeds in 500 times diluted 50% mancozeb for 1 hour, then take out, wash and germinate; or soak the seeds in 150 times diluted formalin for 1.5 hours, then wash and germinate.

③ Rotation with non-melon crops should be carried out for more than 2 years.

④ Use disease-free field soil to grow seedlings. If conditions permit, use soilless seedling technology to prevent seedlings from being infected with diseases.

⑤ Cultivation and management: Ventilation should be strengthened in the protected area to reduce humidity and prevent disease. During cultivation, try to use half-high ridge cultivation, lay mulch, reduce watering times, and reduce field humidity. Drain water in time during the rainy season to prevent waterlogging and ensure that there is no water accumulation in the field. After the harvest, clean the field in time and bury or burn the diseased plant residues.

⑥ For chemical control, in the early stage of the disease, you can use 200×10-6 solution of agricultural streptomycin, or 150-200×10-6 solution of phytosyltransferase, or 500 times solution of DT fungicide, or 500 times solution of antibacterial agent "401", or 600 times solution of 70% DTM, or 250 times solution of 70% aluminum copper formazan. If bacterial angular spot and downy mildew occur at the same time, 35% copper thiophanate-methyl can be used once every 5-6 days, and spray 3-4 times in a row.