Do chemical and biological controls have potential in soybean cyst nematode management?
Some nematicides are registered for use in soybean. A few nematicides are effective in lowering SCN population density, but their performance depends on many soil and environmental factors including soil type, rainfall, soil moisture, temperature, and soil microbial activities. Use of nematicides adds significantly to production costs and does not guarantee increased yields. Economics, as well as environmental and personal health concerns, should be considered before using nematicides. For these reasons, nematicides are not commonly recommended for SCN management.
Although there is no widely accepted commercial biological control agent for SCN management, biological control should be considered as part of an integrated management program. Soybean cyst nematode is subjected to attack by a wide range of natural enemies including fungi, bacteria, predacious nematodes, insects, mites and other microscopic soil animals. The species and activities of natural antagonists vary in different fields. In some soybean fields in Minnesota, high percentages (more than 60%) of the SCN second-stage juveniles are parasitized by the fungi Hirsutella minnesotensis and/or H. rhossiliensis (Fig. 18).
SCN population densities are relatively low in some soils due to biological factors, and these soils are known as nematode-suppressive soils. Some cultural practices may enhance the activities of nematophagous fungi and suppress nematode population densities. For example, monoculture of susceptible soybean for a number of years may increase parasitism of the nematodes by microbial pathogens, and the soil in the field becomes suppressive to the SCN population.
With SCN population densities reduced by natural antagonists, the required time for planting nonhost crops and resistant varieties can be reduced, yield of resistant and susceptible varieties increased, development of virulent HG Type slowed and/or effectiveness of resistant varieties maintained.