Control of top blight of growing soybean

Wudalianchi City is one of the main soybean producing areas in Heilongjiang Province and a major commodity grain county in the country. The sown area of soybean accounts for more than 50% of the total sown area every year. Soybean top blight only occurred sporadically in the past, but there was no large-scale occurrence in 1998. The city has occurred in Taiping Township, Siping Township, Heping Town, Construction Township, Tuanjie Township, Shuangquan Township and Wudalianchi Town, covering an area of 480 hm2. Among them, a piece of land in the central village of construction township 73 hm2, a piece of land in Xinfeng village of Siping township 47 hm2, and a piece of land of Yongan village of Tuanjie township all occurred in the whole field, with a yield reduction of more than 70%. A 71 hm2 soybean field in Longquan Village, Wudalianchi Town, fell ill to varying degrees. Several winds of Grade 3 and 4 from August 3 to 10 toppled 60% to 70% of the soybean plants in the affected plot, resulting in a substantial reduction in yield to no yield and serious losses.

1 symptom

Soybean top blight is a viral disease, and the pathogen is SMV. The disease occurred for a long time in Wudalianchi area this year, from seedling stage to grain filling stage, and the disease was the most serious after flowering stage. The symptoms were brown ring shift and growth point necrosis on the cotyledons of the seedlings, and some seedlings died immediately. The occurrence of dots is dominant in the field. In the infected plants in the early stage of flowering, the internodes of the diseased plants were prolonged, the tip of the stem was prolonged, the apical buds became brown and bent into hooks, and the plants began to become brittle and easy to fall down. From flowering to grain filling stage, if you encounter a wind of about level 3, the diseased plant is easy to fall down to one side with the wind. All the worst-hit plots this year have this symptom. In the susceptible plants from late flowering to seed-filling stage, the buds and leaves are easy to fall, the stem nodes and pith near the branches turn brown, the pods are very small, the pods are not well developed, the seeds in the pods are not full, often delay ripening, and remain green until harvest. According to the results of the investigation on the yield of diseased fields, the average yield of 29 households in Xinfeng Village, Siping Township is less than 5 kg/667 m2; the east of Yongan Village in Tuanjie Township and Longquan Village in Wudalianchi Town are not more than 30 kg/667 m2, which is more than 82% lower than the average yield of 170 kg/667 m2 in the whole city.

2 the regularity of the disease

Soybean top blight is not a common disease in Wudalianchi area, but this year's sudden outbreak caused serious damage. Through analysis, it is concluded that: this year's heavy rain and light is the cause of some diseases, some other important reasons can not be ignored. (1) soybean seeds are infected with disease. The time for the vitality of soybean top blight virus in seeds varies with the temperature conditions of the seed storage period. The longest can be maintained for 5 years at low temperature and 2 years at room temperature. There were also significant differences in resistance among varieties. In the plot investigation of the central village of Construction Township, it was found that there were significant differences in the susceptibility of soybean fields of different varieties of farmers with the same sowing time and similar conditions such as fertilizer and water. In the plot investigation of Longquan Village, Wudalianchi Town, it was found that other conditions were similar but the varieties were different. In the soybean fields of three neighboring farmers, the disease occurred on both sides and the incidence in the middle was less than 10%. (2) soil is poisonous. In the investigation, it was found that there were significant differences in the degree of disease among the plots with the same variety, different previous crops and different ploughing conditions.

3 methods of prevention and control

1) Pesticide control. When it is confirmed that soybean top blight occurs in a large area, chemical control should be taken. In the experiment of Longquan Village, Wudalianchi Town, the spray control of 70% mancozeb wettable powder 500 times, 75% chlorothalonil wettable powder 600 times and 64% chlorothalonil wettable powder 600 times showed that the control effect of detoxification alum was the best, 86.7%, 82.3% and 63% respectively. Because the incidence of soybean top blight is long and chemical control is difficult, prevention is advocated.

2) select resistant varieties. In the investigation, it is found that Hei 1544, Hei 1526, Bei 9395, Bei 9411 and other varieties are resistant varieties, which can be selected in production and should be replaced frequently and should not be used for too long.

3) using disease-free seeds. Strengthen seed quarantine and put an end to seed sowing with disease.

4) the diseased plant should be removed from the plot where the spot film occurs.

5) further promote the seed coating project and the unified seed supply project. At the beginning of this year, under the unified deployment of the municipal party committee and municipal government, our city implemented the seed coating project and the seed supply project. In the investigation of 270t black 1544 and black 1526 seeds supplied by seed company and soybean seed coated with soybean seed coating agent, no occurrence of soybean top blight was found.