What causes bacterial marginal blight of cucumber?

Cucumber is widely cultivated throughout China, and greenhouse or plastic tunnel cultivation is used in many regions; it is now widely grown in temperate and tropical regions. Cucumber is one of the main summer vegetables in all parts of China. In addition, its stem and vine are used medicinally to reduce inflammation, resolve phlegm and relieve spasms. During the actual growing process, bacterial marginal blight of cucumber is very likely to occur. What causes this disease? What symptoms does it have? How should it be prevented and controlled? Let's take a look below.

1. What causes bacterial marginal blight of cucumber?

Pseudomonas marginalis pv. marginalis, a bacterium. The pathogen overwinters on seeds or remains in the soil with diseased plant residues, becoming the primary infection source the following year. The bacterium invades through natural openings such as hydathodes at the leaf margin, and spreads and reinfects through rain and wind, and field operations. It is mainly affected by humidity changes caused by rainfall and by leaf surface condensation. In northern China, greenhouse relative humidity is high in spring and summer; especially at night as the temperature drops, humidity continuously rises to above 70% or saturation, and lasts as long as 7-8 hours, resulting in more severe disease.

2. Symptoms of bacterial marginal blight of cucumber

In bacterial marginal blight of cucumber, the leaves are affected first. Initially, water-soaked small spots appear near the hydathodes, then expand into light brown irregular lesions and spread along the leaf veins toward the leaf blade in a V shape; the lesions look as if scalded by water. Lesions on petioles and stem tendrils are also water-soaked and brown. The fruit begins to soften from the tip. When humidity is high, a large amount of milky white bacterial ooze exudes from the diseased parts, and in severe cases the fruit softens.

3. Treatment methods for bacterial marginal blight of cucumber

1. Seed disinfection

Use constant-temperature dry heat sterilization at 70°C for 72 hours. Soak seeds in warm water at 50°C for 20 minutes, remove and air-dry, then germinate and sow. Soak seeds in 300-fold calcium hypochlorite solution for 30-60 minutes, or in 150-fold 40% formalin solution for 1.5 hours, or in 500-fold 1 million unit streptomycin sulfate solution for 2 hours, then rinse clean and germinate and sow.

2. Agricultural control

Strengthen disease-free production at cucumber seed production bases, and select disease-free fields and disease-free cucumbers for seed saving. Cultivate disease-free strong seedlings using disease-free soil seedbeds. Pay attention to timely ventilation, reduce greenhouse temperature, and increase light. Apply more decomposed organic fertilizer; after disease onset, control irrigation to promote root development. Promote the use of cultivation techniques such as high ridges, film mulching, and subsurface watering. Pay attention to appropriate crop rotation, remove diseased plant residues, and promptly plow and sun the soil.

In protected cultivation greenhouses, promptly clear drainage ditches to prevent water accumulation after rain; watering and fertilizing should be done in the morning on sunny days, and the greenhouse should be opened in time for ventilation and dehumidification. It is recommended to implement alternate-year rotation with non-cucurbit crops to reduce the source of pathogens in the field.

3. Chemical control

In the early stage of bacterial marginal blight of cucumber, spray 72% Kelu wettable powder at 600-750-fold dilution on the leaves, spraying once every 7 days for a total of 4-6 sprays. Other commonly used pesticides include agricultural streptomycin 250 mg/kg solution, new phytomycin 200 mg/kg solution, 14% copper ammonia complex aqueous solution at 300-fold dilution, 3% Kejunkang wettable powder at 800-1 000-fold dilution, and 50% metalaxyl-copper wettable powder at 600-fold dilution. In protected cultivation, dust 15 kg per hectare each time of 10% ethylicin dust, or 5% chlorothalonil, or 10% copper rosinate dust.