Occurrence and Control Methods of Cucumber Gray Mold

In recent years, with the continuous expansion of protected cucumber cultivation areas, gray mold, which was originally a minor disease, has gradually risen to become a major disease and poses a serious threat to production. If not controlled in time, it can cause great losses. According to surveys in Shaocheng District, Wuyi, Jizhou and other places, losses generally reach 15%-20% when the disease occurs, and can exceed 30% during an epidemic. Besides harming cucumbers, this disease also infects tomatoes, eggplants, kidney beans, peppers and many other vegetables. Therefore, attention must be paid to the control of this disease in production.
　　
I. Symptom identification: At the adult plant stage, this disease mainly damages the fruit, and also damages leaves and stems. Young fruits are mostly affected. In most cases, the disease starts on the residual flowers, then damages the tip of the fruit and spreads upward, and in severe cases half or even the entire fruit becomes diseased. The diseased part of the fruit turns brown and rots, with a dense gray mold layer on the surface. When the affected residual flowers or diseased fruits fall onto leaves or stems, they can cause disease on the leaves or stems. When leaves are affected, the fallen residual flowers are mostly the center, spreading outward to form large nearly round lesions, with a small amount of gray mold layer on the surface. When they fall on stems, the stems break, and in severe cases the whole plant dies.
　　
II. Pathogen: Cucumber gray mold is caused by the fungus Botrytis cinerea of the Deuteromycotina. The disease overwinters as mycelium or conidia attached to seeds and diseased residues, remaining in the soil, or spores transmitted through the air from other hosts are the source of primary infection. Secondary infection spreads through airflow, rainwater and agricultural operations.
　　
III. Conditions for disease occurrence:
3.1 The optimum temperature for pathogen development is 18°C-23°C, the relative humidity is above 90%, and weak light is suitable for disease occurrence.
3.2 When there are many consecutive cloudy days, low temperatures, high humidity inside the greenhouse, long dew formation periods, and untimely ventilation, gray mold will occur severely.
　　
IV. Control measures:
The control of cucumber gray mold should combine the control and regulation of the relative temperature in protected cultivation during the fruiting period with timely, rational and rotational use of chemicals:
4.1 The cucumber field should not be low-lying and waterlogged; prepare the land with deep furrows and high beds, and it is best to plant with plastic film mulching; during field management, pay attention to guiding the vines in time and removing excess side branches to ensure good ventilation and light transmission in the field during the fruiting period; in protected cultivation, pay attention to frequently opening the side windows and roof windows during the fruiting period to reduce the temperature.
4.2 From 5-7 days before the peak fruiting period, promptly remove diseased leaves, yellow leaves, diseased flowers and diseased fruits to reduce the pathogen source and keep the field clean.
4.3 At the early stage of disease occurrence, use appropriate chemical control.
4.3.1 Fumigate with 20% Procymidone smoke agent, 300-400 g per mu each time;
4.3.2 50% Sumeike wettable powder 1000 times;
4.3.3 22% chlorothalonil smoke agent, 200 g per mu each time, ignited at the lowest point of the greenhouse in the evening;
4.3.4 50% iprodione wettable powder 1500 times solution;
4.3.5 65% Kangmeiwei wettable powder 1500 times solution;
4.3.6 40% Baikening suspension concentrate 600-800 times solution;
4.3.7 70% Pujunke wettable powder 800-1000 times;
4.3.8 58% Huimeibiqing wettable powder 800-1000 times solution;
4.3.9 28% chlorothalonil wettable powder 800 times solution.
The above chemicals can be used in rotation or in combination, once every 7-10 days, with 2-8 consecutive applications.
　　
V. In the process of chemical spray control, to improve efficacy, pay attention to the following points:
5.1 Spraying is best done on sunny days. Ventilate before spraying, and spray after the water droplets on the leaf surface have dried. Generally, spray before 10 a.m. or after 4 p.m.;
5.2 When spraying, neither miss any area nor spray repeatedly.
5.3 When spraying, be sure to spray from the lower part of the cucumber plant upward, focusing on the underside of the leaves.
5.4 When spraying, appropriately add a spreading agent, such as Gaotaimo, so that the solution adheres evenly to the plants to improve the control effect.