What are the control methods for soybean bud blight?
Wudalianchi City is one of the main soybean-producing areas in Heilongjiang Province and a major national commodity grain county. Soybean planting area accounts for more than 50% of the total sown area every year. Previously, soybean bud blight occurred only sporadically in the local area, and the large-scale outbreak in 1998 was unprecedented in recent years. In the city, it occurred in Taiping Township, Siping Township, Heping Town, Jianshe Township, Tuanjie Township, Shuangquan Township, and Wudalianchi Town, covering an area of 480 hm2. Among them, a 73 hm2 field in Zhongxin Village, Jianshe Township, a 47 hm2 field in Xinfeng Village, Siping Township, and a 34 hm2 field in Yong'an Village, Tuanjie Township all had the disease across the entire field, with yield reductions of more than 70%. A 71 hm2 soybean field in Longquan Village, Wudalianchi Town, was affected to varying degrees, and several Force 3 to Force 4 winds from August 3 to 10 caused 60% to 70% of the soybean plants in the affected plots to lodge, resulting in severe yield reductions up to total crop failure and serious losses.
1 Symptoms
Soybean bud blight is a viral disease, and the pathogen is SMV. This year, the occurrence period of this disease in the Wudalianchi area lasted a relatively long time, occurring from the seedling stage to the seed-filling stage, with the most severe incidence after the flowering stage. Symptoms include brown ring spots on the cotyledons of seedlings, necrosis of the growing point, and some seedlings dying soon afterward. In the field, it mainly occurs in patches. In plants infected before flowering, the internodes of diseased plants lengthen, the stem tip extends, the terminal bud turns brown, and it bends into a hook shape; the plants begin to become brittle and prone to lodging. From flowering to the seed-filling stage, if a Force 3 or so wind is encountered, diseased plants readily lodge in one direction along the wind. This year, the most severely damaged fields all showed these symptoms. In plants infected from the late flowering stage to the seed-filling stage, buds and leaves drop easily, the stem node area near the branches and the pith turn brown, pods are very small, development is poor, seeds within the pods are not plump, and maturity is often delayed, with the plants remaining green until just before harvest. Based on yield survey results from affected fields, the average for 29 farming households in Xinfeng Village, Siping Township, was below 5 kg/667 m2; the east field of Yong'an Village, Tuanjie Township, and Longquan Village, Wudalianchi Town, also did not exceed 30 kg/667 m2, which is a yield reduction of more than 82% compared with the city average of 170 kg/667 m2 in unaffected fields, and the seeds were not plump and of poor quality.
2 Occurrence pattern
Soybean bud blight is not a commonly occurring disease in the Wudalianchi area, but this year it suddenly broke out and caused severe damage. After analysis, it is believed that in addition to the rainy and low-light conditions this year being a cause of the frequent occurrence of some diseases, some other important causes cannot be ignored. (1) Soybean seeds carrying the disease. The time for which soybean bud blight virus remains viable in seeds varies with the temperature conditions during seed storage. Under low-temperature conditions, it can remain viable for up to 5 a, and at room temperature it can also remain viable for 2 a. There are also obvious differences in resistance among varieties. In a field survey in Zhongxin Village, Jianshe Township, it was found that among farming households with the same sowing time and similar fertilizer and water conditions but different varieties, the degree of disease incidence in soybean fields differed markedly. In a field survey in Longquan Village, Wudalianchi Town, it was found that with other conditions similar but varieties different, among the soybean fields of 3 adjacent farming households, both sides were entirely affected while the middle one had an incidence of less than 10%. (2) Soil carrying the virus. In the survey, it was found that fields with the same variety but different previous crops and different plowing conditions also differed markedly in disease incidence.
3 Control methods
1) Chemical control. When it is confirmed that soybean bud blight is occurring on a large scale, chemical control should be adopted. When the disease occurs at the soybean flowering stage, according to a trial in Longquan Village, Wudalianchi Town, spraying with 70% mancozeb wettable powder at 500 times dilution, 75% chlorothalonil wettable powder at 600 times dilution, and 64% oxadixyl-plus wettable powder at 600 times dilution showed that oxadixyl-plus had the best control effect at 86.7%, followed by chlorothalonil at 82.3%, and mancozeb at 63%. Because the occurrence period of soybean bud blight is relatively long, chemical control is relatively difficult, so prevention first is advocated.
2) Select resistant varieties. The survey found that varieties such as Hei 1544, Hei 1526, Bei 9395, and Bei 9411 are resistant varieties and can be selected in production, and they should be changed frequently rather than used for too long.
3) Use disease-free seeds. Strengthen seed quarantine work and prevent the sowing of diseased seeds.
4) In plots with patchy occurrence, remove diseased plants.
5) Further advance the seed coating project and the unified seed supply project. Earlier this year, under the unified arrangements of the municipal party committee and municipal government, our city implemented the seed coating project and the unified seed supply project. In a survey of soybean fields planted with 270 t of Hei 1544 and Hei 1526 seeds uniformly supplied by the seed company and with seeds coated using soybean seed coating agent, no occurrence of soybean bud blight was found.