What are the latest control methods for wheat powdery mildew?
Wheat powdery mildew is a worldwide disease, found in all major wheat-producing countries. In China it occurs commonly along the coast of Shandong, in Sichuan, Guizhou and Yunnan, and in recent years it has shown an increasingly serious trend in the wheat regions of Northeast, North and Northwest China. It can infect all aboveground organs of the wheat plant, but mainly the leaves and leaf sheaths; in severe cases the glumes and awns can also be affected. Let us take a look at the control methods for wheat powdery mildew!
Symptoms of damage
Wheat powdery mildew can infect all aboveground organs of the wheat plant, but mainly the leaves and leaf sheaths; in severe cases the glumes and awns can also be affected. At the initial stage, white mildew spots 1-2 mm appear on the leaf surface, then gradually expand into nearly round to oval white mildew patches. The surface of the mildew patches has a layer of white powder that disperses immediately when subjected to external force or vibration; these powdery substances are the mycelium and conidia of the fungus. Later the mildew layer on the diseased part turns grayish white to light brown, and small black grain-like dots the size of a pinhead, namely the cleistothecia of the pathogen, are scattered on the lesions.
Conditions for disease occurrence
In winter wheat regions, the inoculum in spring mainly comes from local sources; in spring wheat regions, besides local sources, it also comes from nearby areas where the disease occurs early. The optimum temperature for occurrence is 15-20°C; below 10°C the disease develops slowly. A relative humidity greater than 70% may cause an epidemic. In areas with little rain, the disease is severe in years with much rain; in rainy areas, if there are too many rain days and too much rainfall, the disease is instead slowed, because continuous rain washes away the surface conidia. Excessive nitrogen application causes the plants to stay green late and the disease to be severe. Improper management, insufficient water and fertilizer, dry soil, weak plant growth and low disease resistance also make the disease likely to occur; in addition, high density leads to severe disease.
Control methods
1. Plant disease-resistant varieties, which can be selected according to local conditions. For example, Beijing winter wheat currently uses Jing 411 as the main variety; for high-fertility wheat fields, Jingdong 8, Jingdong 6 and Zhongmai 9 can be planted in combination; for medium-fertility fields and those with poor irrigation conditions, drought-resistant and barren-tolerant varieties such as Jing 437, Jinghe 1 and Lunkang 6 can be planted; for rice-stubble wheat and late-sown wheat fields, Jing 411, Jingdong 8 and Jingshuang 18 can be selected.
2. Advocate the application of compost fermented with effective microorganisms or decomposed organic fertilizer, adopt formula fertilization technology, appropriately increase phosphorus and potassium fertilizer, and carry out rational close planting according to variety characteristics and soil fertility. In southern wheat regions, drain water promptly after rain to prevent moisture retention. In northern wheat regions, water at the right time so that the host enhances its disease resistance.
3. In areas where volunteer wheat seedlings oversummer, remove volunteer wheat promptly before autumn sowing of winter wheat, which can greatly reduce the inoculum for autumn seedlings. Treat seeds with 25% triadimefon (Bayleton) wettable powder at 0.03% of seed weight (active ingredient); alternatively, use 20-25 g of 15% triadimefon wettable powder to treat 667 sq m of wheat seed to control powdery mildew, and also control smut and stripe rust.
4. In areas where there are few resistant wheat varieties or where pathogen races vary greatly and resistance is lost quickly, when the disease index of wheat powdery mildew reaches 1 or the rate of diseased leaves exceeds 10%, begin spraying 20% triadimefon emulsifiable concentrate at 1000 times dilution or 40% Fuxing emulsifiable concentrate at 8000 times dilution. Field conditions can also be used to mix insecticides and fungicides so as to apply a single treatment at the critical period, controlling major pests and diseases such as wheat powdery mildew and rust.
5. In the middle and late stages of wheat growth, when stripe rust, powdery mildew and ear aphids occur together, use per mu 7 g active ingredient of triadimefon plus 3 g active ingredient of pirimicarb plus 150 g potassium dihydrogen phosphate. In areas or fields where stripe rust, powdery mildew, wheat blossom midge and armyworm occur together, use per mu 7 g active ingredient of triadimefon plus 40% omethoate at 2000 times dilution plus 150 g potassium dihydrogen phosphate. In areas where head blight, powdery mildew and ear aphids occur together, use per mu 40 g active ingredient of carbendazim plus 7 g active ingredient of triadimefon plus 3 g active ingredient of pirimicarb plus 150 g potassium dihydrogen phosphate.