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Bacterial blight is a severe disease that affects both spring and summer-sown cucumbers, causing significant damage to the plants. The disease primarily targets the stems and leaves. When it first appears on the stems and their bases, the lesions are round or elongated, yellow-brown in color, oily-looking, slightly sunken, and exude amber gum. Black spots often appear on the surface of these lesions. On the leaves, large, irregularly shaped lesions form, often starting from the edges and developing into V-shaped or semi-circular brown areas. As the disease progresses, the lesions become brittle and may tear easily. These affected areas are densely covered with small black dots. Lesion sizes can range from 10 to 35 cm in diameter, with some being even larger. Infected leaves turn yellow from the bottom up but do not fall off easily. In severe cases, only the top 1-2 leaves remain. Unlike wilt diseases, bacterial blight does not cause discoloration of the vascular bundles or lead to plant death, which is a key distinguishing feature.
The pathogens responsible for this disease overwinter in infected plant debris and soil. They are typically spread through irrigation water, wind, and can enter the plant through stomata, lenticels, or wounds. Infected seeds can also lead to early infection in the cotyledons. Factors such as high temperature and humidity, poor air circulation, excessive nitrogen fertilizer application, improper vine training, flooding irrigation, heavy rainfall, weak plant growth, and continuous cultivation in previously infected fields increase the risk of disease occurrence.
To prevent bacterial blight, several effective measures can be taken. First, implement crop rotation with a gap of more than two to three years, and select disease-free seeds or plants from healthy sources. Second, improve seedling management by using balanced fertilization, especially increasing phosphorus and potassium to enhance plant resistance. Ensure good ventilation and light exposure, manage temperature and humidity levels, and create a better microclimate in the field. Third, apply chemical treatments at an early stage. Options include 75% chlorothalonil wettable powder diluted at 600 times, 70% thiophanate methyl wettable powder at 800 times, 50% carbendazim wettable powder at 1500 times, or 45% chlorothalonil smoke agent at 250 grams per acre. Another option is 40% Fuxing Star emulsifiable concentrate diluted at 800 times. Apply these treatments every 7 to 10 days, repeating the process 3 to 4 times for optimal control.