Most of you already know that the soybean cyst nematode (SCN) is the most damaging pathogen to soybeans. There are currently two widely recommended options for combatting this microscopic worm.
1) Rotate crops
2) Plant resistant varieties
Unfortunately, both of these accepted strategies have limitations.
Rotation is essential for preventing a buildup of SCN populations. However, the biology of SCN allows the worm to survive long periods without a soybean host. As an egg in the soil, SCN can sense the presence of soybean. If SCN senses that soybeans aren’t around (i.e., if corn is there) then it will simply go to sleep and wait for a soybean to be planted. SCN can stay in this hibernating state for 10 years! So unless you move to a continuous corn production system, rotation will not rid your field of SCN.
Resistance is normally recommended for control of SCN. The good news is that a large number of commercial soybean varieties have SCN resistance. However, more than 90% of SCN-resistant commercial soybean varieties derive their resistance from a single genetic parent, which goes by the catchy name of “PI 88788”. This resistance is often advertised as providing control to race 3 of SCN. The bad news is that we see more and more SCN populations able to reproduce on plants with the PI 88788 source of genetic resistance.
So, should we all give up and start planting wheat instead of soybeans? No. SCN is rarely an immediate death sentence for soybean production. Instead, SCN typically leads to a general decline in soybean productivity over time. While many SCN populations can reproduce on PI 88788, this does not mean that resistance is completely ineffective. Depending on the SCN populations, these “single-source” PI 88788 resistant varieties still provide a certain level of protection. Furthermore, there are other sources of resistance out there. Breeders are hard at work trying to combine these other sources of resistance with the high-yielding traits that you desire. In addition, several companies have developed seed treatments for controlling SCN. While it is too early to say how effective these seed treatments are, they do add another weapon to your SCN arsenal.
Finally, there are nematologists such as myself who are playing the long game. One of my research projects is focused on understanding the nervous system of SCN. How does SCN find soybeans in soil (they don’t have eyes)? How do they know when to “go to sleep” when soybeans aren’t around? How do they know when to “wake up?” If we obtain a better understanding of how this animal can sense and respond to its environment, we can develop new ways of battling this foe.
The approaches available today—including rotation, resistance and seed treatments—are a partial remedy to a big problem. Scientists are slowly uncovering the secrets of SCN biology that will provide stronger long-term control to this important pest.
Nate Schroeder is an Assistant Professor in the Department of Crop Sciences at the University of Illinois. His area of work focuses on the study of nematodes. Read more about Nate here.