What to Do About Soybean Cyst Nematode (Dahuolong Yangzi)? A Detailed Guide to Prevention and Control

Soybean cyst nematode disease

Soybean cyst nematode disease, also known as Verticillium wilt, yellow dwarf disease, and root nematode disease, is called "dahuolong yangzi" by farmers. According to reports, more than 22.5 million mu of soybeans in 14 provinces, municipalities, and autonomous regions in China have been infected with this disease. Soybean cyst nematode disease damages the soybean root system, causing poor growth and development of the aboveground parts of the plant, shortened and dwarfed internodes, yellowing leaves, reduced pod set, and lower yield, with general yield reductions of 10%-30%. Severely affected fields may suffer almost total crop loss. After soybeans are parasitized by nematodes, the main root and lateral roots develop poorly, fibrous roots increase, and the entire root system becomes thread-like fibrous roots, with few or no root nodules. White or yellow-white protrusions the size of a needle head, 0.5 mm in diameter, appear on the roots; these are the cysts of the nematodes.

Soybean cyst nematode disease spreads through soil, water, birds, and wind. Viable eggs in the soil can survive for 9 years without a host plant, and can survive on seeds for 22 months. These eggs can also survive and reproduce on weeds and other crops (such as kidney beans, clover, white clover, vetch, etc.). When soybeans are sown and roots form, 48 hours later the cyst nematodes can invade the root at the edge of the central cylinder, insert their heads into the central cylinder, and begin feeding. After 3 molts they become adults. At this point, the body of the female adult swells into a cyst, breaking through the root epidermis and exposing itself outside the root, while the head remains inserted in the original place. The male adult leaves the root and enters the soil to find a female for mating. In our province, white cysts begin to appear in mid-June, and the second generation is completed by the end of June; the third generation is completed in late July and early August; another generation is completed in early September. They can reproduce 3-4 generations per year, with one generation taking 34-44 days, and as short as 19 days. The cysts drop into the soil as the root system distributes and sheds, with the most, about 90%, found in the 0-20 cm plough layer.

Symptoms at the seedling stage are yellowing of the cotyledons and true leaves and stunted development. Most nematodes suck sap from the soybean roots, seriously affecting seedling growth and development. In the authoritative stage, affected plants are short and small, the leaves gradually yellow from bottom to top, growth is slow, flowering is delayed, pod set is reduced, and beans are shriveled; in severe cases, plants die after flowering. Another feature of the disease is an underdeveloped root system, few lateral roots, many fibrous roots, small and few root nodules, and many small white or yellowish-white granules attached to the fibrous roots.

At present, the main measures for controlling soybean cyst nematode are:

1. Reasonable crop rotation: rotate soybeans with non-host plants such as corn and small-grain crops to reduce or avoid continuous and alternate-year soybean cropping.

2. Increase manure application, with well-balanced farmyard manure giving the best effect. The Heilongjiang Institute of Agricultural Modernization, starting from nutrition science and after years of experiments and demonstrations, developed a soybean continuous and alternate-year cropping yield-preserving agent and a soybean yellow wilt foliar spray. The yield-preserving agent is applied at 1.5 kg per mu as a base fertilizer at sowing, increasing yield by an average of 22.5 kg per mu, or 22.1%. The yellow wilt foliar spray applied at the seedling and flowering stages increases yield by 13.6%.

3. Chemical and biological control. Tests show that 3% carbofuran has the best control effect, reaching over 90%. Ethyl thiocyclophosphorus and 391 also work; after soybean harvest, planting non-host plants such as hemp and sweet clover the following year can alleviate cyst nematode damage.

4. Disease-resistant varieties. Selecting nematode-resistant varieties is an important measure for increasing yields of continuous and alternate-year soybeans. Choose Kangxian No. 1 and No. 2 from the Saline-Alkali Soil Institute of the Provincial Academy of Agricultural Sciences, and nematode-resistant varieties bred by the Nenjiang Institute and the Provincial Academy of Land Reclamation Sciences for planting.

Physiological diseases

So-called physiological diseases refer to diseases caused by nutrient deficiency and deterioration of the ecological environment in soybeans. For example, due to deficiency diseases, soybeans lacking major nutrient elements such as potassium and nitrogen and trace nutrient elements such as zinc, boron, molybdenum, and manganese may suffer diseases such as white seedling disease and flowering-stage infertility. At the same time, because plant growth and development are hindered and vigor is weak, the whole plant grows in a diseased state and is highly susceptible to root rot, cyst nematode disease, and other pest and disease damage. Farmers are advised to choose and apply the soybean continuous and alternate-year cropping yield-preserving agent and the soybean yellow wilt foliar spray. They have good effects, low cost, and obvious economic benefits. At present, during the peak period of soybean dahuolong yangzi damage, comprehensive measures are recommended for control, spraying the yellow wilt foliar spray once every 7-10 days, 2-3 times over the whole growth period.