How to prevent vegetable diseases on smoggy days?
In winter, smoggy days and weather with low temperatures and scant sunlight increase, especially in the central part of our province and the Beijing-Tianjin area, which has brought a certain impact on vegetable production and will aggravate the occurrence of diseases. Here, it is suggested that the vast number of vegetable growers prevent the occurrence of vegetable diseases from the following aspects.
1. Increase light
On smoggy days, straw mats and cotton quilts should be opened every day so that vegetables can use scattered light for photosynthesis; choose greenhouse films with good light transmittance and clean the greenhouse film in time to enhance light transmittance; if conditions permit, artificial supplemental lighting can be carried out by installing supplementary lamps and hanging reflective curtains on the back wall.
2. Water less
On smoggy days, vegetable roots grow weakly and the metabolic level is low, so it is not suitable to water heavily. Watering should be done reasonably according to weather conditions, and drip irrigation under film should be adopted for watering, strictly controlling the humidity in the greenhouse and avoiding the occurrence of a low-temperature and high-humidity environment, so as to prevent diseases.
3. Fertilize less
On smoggy days, it is not suitable to apply large amounts of fertilizer. An appropriate amount of carbon dioxide gas fertilizer can be added. After the weather turns clear, an appropriate amount of clean water and foliar fertilizer can be sprayed on the leaves. After the vegetables resume normal growth, normal water and fertilizer management can be carried out.
4. Chemical control of common diseases
1. Tomato gray mold. It is one of the diseases most prone to occur in winter greenhouse tomatoes. Gray mold infects tomato leaves, stems, flowers, and fruits, but damage to green fruits is more serious. To control tomato late blight, long-term excessive humidity in the greenhouse should be avoided, ventilation should be done in a timely manner, and diseased plants should be removed promptly at the early stage of the disease. For chemical control, 250 g/L azoxystrobin suspension concentrate, 70% propineb wettable powder, 100 g/L cyazofamid suspension concentrate, and 72% cymoxanil mancozeb wettable powder can be selected for spraying.
2. Cucumber sclerotinia rot. Humidity in the greenhouse higher than 85% is conducive to the occurrence of sclerotinia rot. Young cucumbers and stems in the middle and lower parts of the plant are often severely affected. When young cucumbers are infected, infection mostly starts from the top, initially appearing as water-soaked dark green rot, and later dense cottony white mold is produced on the diseased part. When environmental conditions are suitable, the white mold on the diseased part turns into black mouse-dropping-like sclerotia. When the stem is damaged, faded water-soaked lesions begin to appear, followed by softening and rotting, white cottony mycelium is produced on the diseased part, and later black mouse-dropping-like sclerotia are formed.
For chemical control, 50% boscalid water-dispersible granules, 50% procymidone carbendazim wettable powder, 25% carbendazim wettable powder, 255 g/L iprodione suspension concentrate, or 25% prochloraz emulsifiable concentrate can be used for spraying.
3. Cucumber downy mildew. This disease mainly occurs on leaves. Diseased leaves initially show light green water-soaked spots, which after expansion are restricted by leaf veins and become polygonal, changing from yellow-green to light brown. In the later stage, the lesions merge into patches, and the whole leaf dries up. When moist, gray-black mold grows on the lesions on the underside of the leaves, and in severe cases the leaves of the whole plant wither and die.
To control cucumber downy mildew, it is particularly important to make use of the closed characteristics of protected cultivation to create an environment with high temperature and low humidity. Before consecutive smoggy, overcast, and rainy weather arrives, spraying protective fungicides or fumigation with chemicals can achieve a relatively good preventive effect, such as 45% chlorothalonil smoke agent, etc. At the early stage of the disease, 20% flumorph wettable powder, 250 g/L azoxystrobin suspension concentrate, or 80% dimethomorph water-dispersible granules can be sprayed for control.
Yixian County Agriculture Bureau Yu Lianguo