What is the impact of climate change on major soybean diseases and insect pests?

Due to the change of climatic conditions, soybean diseases and insect pests will occur in some soybean planting areas. Soybean diseases mainly include soybean root rot, soybean Sclerotinia sclerotiorum and soybean cyst nematode. Many leaf diseases also occurred in different degrees in different years, and soybean gray leaf spot disease has been controlled in a large area. Soybean pests mainly include soybean moth, soybean aphid, soybean thrips, soybean red spider, two-leaf beetle, soybean leaf roller and so on.

Soybean root rot: Low soil temperature and high humidity are beneficial to soybean root rot. Soybean root rot is the general name of root fungal diseases in soybean seedling stage.

Soybean Sclerotinia sclerotiorum: Long-term cold and wet weather is beneficial to the occurrence of soybean Sclerotinia sclerotiorum, which is more serious in low-lying land and high density. In the middle and late July, the continuous low temperature and scanty illumination at the temperature of 65438 08 ~ 22℃ are conducive to the germination of pathogenic fungi ascospores and become the primary source of infection. Sclerotinia sclerotiorum is common in soybean producing areas where sunflower and rape are grown. The northern part of Heilongjiang Province and the eastern part of Inner Mongolia Autonomous Region are seriously ill, with the incidence rate of serious plots reaching 1 0,000%, and the output decreased by more than 60%.

Soybean cyst nematode disease: the nematode can survive in soil for 9 years through soil transmission. The longer the drought year and continuous cropping period of soybean, the more serious the damage, which is one of the main diseases in soybean production in China.

Soybean gray leaf spot: rainy weather and high temperature from pod setting to filling stage are beneficial to the occurrence of this disease; The rivers and lakes along the Yangtze River have low terrain and high microclimate humidity, which is beneficial to the occurrence of soybean gray leaf spot. Soybean gray leaf spot is common in northeast soybean area, which can cause large area and large yield reduction in epidemic years.

Soybean downy mildew: the disease is suitable for warm and high humidity environment. The suitable temperature range is10 ~ 30℃; The optimum ambient temperature is 20 ~ 24℃ and the relative humidity is above 90%. The most suitable growth period is the adult stage. The incubation period is 5 ~ 10 days. The average daily temperature 17 ~ 20℃ is the most likely to cause disease.

Soybean virus disease: Drought and lack of rain are beneficial to the growth and activities of aphids, who are the main vectors of soybean virus disease, especially in April-May, which makes soybean virus disease serious. Virus diseases occur in both northern and southern soybean areas of China, and the virus diseases in the south are generally more serious than those in the north. In the epidemic years of individual diseases in Huanghuai bean area, the yield was reduced by 50% due to illness. Virus disease mainly causes mottled seeds in the north, which affects the quality, price and export of commercial beans.

Soybean rust: heavy rainfall, rainy days, long hair and serious illness. In the early sowing period of autumn soybean in South China, soybean rust is serious, and the disease resistance among varieties is different, which is seriously damaged at the filling stage. Soybean rust is very serious in the south of the Yangtze River, and it often wreaks havoc in Guangdong, Fujian and Taiwan Province provinces, causing serious losses. Especially in the wet rainy season, the diseased leaves quickly dried up and fell off, and died 15 ~ 20 days earlier, the weight of 100 grains decreased by 3% ~ 50%, and the yield generally decreased 10% ~ 30%. This disease is easy to spread in areas where the daily average temperature is below 28℃. It is generally not easy to get sick before flowering, but easy to get sick after flowering. The closer you get to maturity, the more vulnerable you are.

Soybean moth: closely related to rainfall. Adults with high temperature and low humidity have short life span, which also affects the development and hatching of eggs. The adaptability of pupae to environment is lower than that of larvae. If it is buried below 3 cm, or if the soil moisture is below 5%, seedlings cannot emerge at all. Every year, 1 generation occurs everywhere, and the mature larvae overwinter in the soil with cocoons. It occurs in all soybean producing areas in China, and the three northeastern provinces suffer the most, which is one of the main soybean pests.

Soybean aphid: The occurrence was affected by the climatic conditions from June to July of that year, with the temperature of 20 ~ 24℃ and the relative humidity below 78%, which was most suitable for soybean aphid breeding and the disease was serious. If the average temperature is higher than 25℃ and the relative humidity is over 80% for five consecutive days, soybean aphids can die in batches. The occurrence of soybean aphid is also closely related to the number of overwintering hosts, climatic conditions and days. Soybean aphids are distributed in all soybean producing areas in China, and the three northeastern provinces, Hebei Province and Henan Province are more harmful.

Soybean red spider: It has 8 ~ 12 generations a year in Heilongjiang Province. The development starting temperature is 10.5℃, the upper limit temperature is 42℃, and the first generation effective accumulated temperature is 163.25℃. When the relative humidity is 35% ~ 55% and the average temperature is 22 ~ 28℃, the development time from egg to adult is the shortest, only 10 ~ 13 days. Therefore, when the drought duration exceeds 14 days, the reproduction speed is the fastest and the damage is the most serious. When the relative humidity exceeds 70%, it is not conducive to the occurrence of red spiders, and the low temperature, rainy and windy weather is also not conducive to the reproduction of red spiders. Soybean red spider occurs all over China, and soybeans in northeast soybean producing areas and Huanghuai River basin are seriously damaged by red spider.

Soybean thrips: It occurs more seriously in years with warm climate, abundant sunshine, little wind and mild drought. The main pests of soybean are soybean thrips and tobacco thrips. Northeast China has 5 ~ 6 generations a year, and overwinters as adults on thistles and other weeds.

Dicotyledonous beetle: Most adults lay eggs in the topsoil of soybean fields. In case of drought, the low humidity of topsoil will affect the hatching of eggs. It occurs in all soybean producing areas in China. Most of these two species overwinter in the soil as adults. Due to the different heating time in different places, the unearthed time of overwintering adults is also different, and the south is earlier than the north. For example, in Jiangsu province, the overwintering adults began to be unearthed in early and middle April, which harmed spring soybean seedlings from late April to late May and summer soybean seedlings in June. In Hubei province, overwintering adults harmed early sowing soybean seedlings in the middle and late April. From late April to early May in Liaoning Province, soybean seedlings began to be damaged in the middle and late May in Heilongjiang Province, and the damage peak was in June.

Soybean root rope: the temperature is high from late May to late June, which is suitable for pests, continuous cropping, weeds and early sowing.

Soybean root-knot nematode disease: It mainly occurs in sandy loam areas with warm climate, which is seriously harmful in southern China, and also occurs in northern soybean areas such as Shandong Province, Hebei Province and Liaoning Province.

Pod moth: it mainly occurs in soybean fields with heavy rainfall and high temperature, and the harm degree is light; Those with less rainfall and low temperature suffer greatly; Continuous cropping land, sloping land and hilly land were seriously affected.

Grasshopper: It is related to the average temperature in early spring of that year. Usually, overwintering adults begin to appear when the temperature reaches 14 ~ 15℃, and reach the peak when the average temperature reaches 17℃. Temperature and humidity play an extremely important role in the dynamics of meadow moth and population.

(Hu Guohua)