What is Soybean Cyst Nematode?

SCN, like all plant-parasitic nematodes, is a microscopic roundworms very simple animal, related to the animal-parasitic roundworms that infect livestock and pets. The infective juvenile is the second-stage juvenile, so-called because it molts once in the egg from first- stage to second-stage.

The infective juvenile of SCN is invisible to the naked eye. Its length is about 1/64 inch.

The juveniles penetrate soybean roots and cause the formation of specialized feeding cells in the root's vascular system (veins). If the juvenile becomes a male, it leaves the root and moves through the soil and probably does not contribute further to plant damage. If the juvenile becomes a female, it loses the ability to move and swells to a lemon-shape as it matures. The young adult female is referred to as a white female. Plant damage is primarily due to the feeding of females.

White females on soybean roots are visible to the naked eye, about the size of the period at the end of this sentence. Nitrogen-fixing nodules are much larger.

White females become yellow as they age and then brown after they die. The brown stage is the cyst for which the nematode is named. Each cyst can contain up to 500 eggs, but under field conditions usually contain many fewer eggs. The cyst protects the eggs from the soil environment.

This SCN cyst has been broken open to reveal the eggs inside. Eggs can remain viable for years even in the absence of a suitable host.

SCN can complete up to six generations during the growing season, depending on:

planting date
soil temperature
length of growing season
host suitability

SCN cannot reproduce without a host plant. Conditions that favor soybean plant growth are favorable for SCN development.