What are the control methods for wheat powdery mildew?
In recent years, with the improvement of fertilizer and water conditions in wheat fields and the increase in plant density in high-yield fields, wheat powdery mildew has become increasingly severe year by year. After the powdery mildew pathogen parasitizes wheat, the plant's respiration increases, transpiration intensity rises, and photosynthetic efficiency decreases, seriously affecting the normal growth and development of wheat. Wheat leaves wither early, tillering and spike-forming rates decrease, and 1000-grain weight drops, causing yield reduction. According to surveys, when wheat is affected by powdery mildew, severely affected fields can suffer a yield reduction of 20%~30%.
Symptoms: Wheat powdery mildew mainly occurs on leaves, but can also occur on leaf sheaths, stems and spikes. Generally, there are more lesions on the upper side of leaves than on the underside, and lower leaves are more severely affected than upper leaves. The surface of the diseased area is covered with a white powdery mold layer. White filamentous mold spots first appear on the diseased area, gradually expand and merge with each other, forming larger long-oval mold spots. In severe cases, they can cover most or even all of the leaf, and the mold layer can reach about 2 mm in thickness, gradually becoming powdery. Later, the mold layer gradually changes from white to gray, with black granules forming on it. Leaves turn yellow early, curl and die, and severely diseased plants are often stunted and unable to form spikes.
The occurrence and development of wheat powdery mildew are closely related to meteorological conditions, variety resistance and cultivation management levels. When the temperature is 15~20°C and the relative humidity in the field is above 70%, the disease develops rapidly. Wherever there is heavy fog and dew and rising temperatures, the disease is severe, and high field humidity favors infection. Excessive application of fertilizer and water, excessive wheat growth, excessive plant density, poor ventilation, high field humidity, and tender plants with low disease resistance also make powdery mildew very likely to occur.
Control methods:
1. Selecting disease-resistant varieties is an effective method.
2. Eliminate the primary infection sources, such as eliminating volunteer wheat seedlings or gramineous weeds at the field edges as much as possible before sowing.
3. Rational fertilization and close planting. Nitrogen, phosphorus and potassium fertilizers should be applied in a balanced way, with appropriate increases in phosphorus and potassium fertilizers. Density should not be too high, and attention should be paid to ventilation and light penetration in the field.
4. Chemical control.
Chemical control can achieve obvious results in stopping the spread of the disease. The number and timing of applications can be determined according to how early or late the disease occurs, the severity of the condition and the type of chemical. Generally, application begins from the jointing stage to the booting stage to full heading, spraying once every 7~10 days, for a total of 2~3 sprays to achieve good results. Chemicals include carbendazim, thiophanate-methyl, tebuconazole, triadimenol, etc.