By Jon Zuk
If you grow soybeans, you’re no doubt familiar with soybean cyst nematode — a highly destructive plant-parasitic roundworm that’s been estimated to cause more than $1 billion in yield losses annually in the U.S.
What makes SCN particularly insidious is that it’s nearly impossible to detect aboveground, since the worms penetrate and feed on soybean plant roots and the cyst itself is about the size of a grain of sand. Females can lay in excess of 200 eggs, and the cyst that is formed by her body after she dies can allow some eggs inside to survive for 10 years or more.
Damage from SCN includes root stunting and disruption of tissue flow and vascular formation in soybean plants. Here’s how to determine if you have SCN in your fields and steps to take to help manage it.
How to tell if you have SCN
Soil sampling is the only way to measure SCN levels. I recommend sampling in the fall and spring of a soybean year. If you can only sample once, sample in the fall after soybean harvest. That way, you can take a sample from the root zone where your soybeans were growing. This sample will tell you what your high SCN levels are and help you prepare for any crop rotation you want to do in the future. If you are soil sampling in a field that has been rotated from soybeans to a non-host crop such as corn or oats, you can take the soil sample anywhere in the field.
Remember, just because SCN isn’t visible aboveground doesn’t mean you shouldn’t scout your fields. If you have areas of brown stem rot or sudden death syndrome and haven’t had them before, take soil samples in these spots to see whether SCN is creating the infection point for those diseases. Even if sampling results indicate you have zero or very low SCN levels, you should still take precautions to manage it. Those results just might mean you don’t have extremely high SCN populations, not that there isn’t any threat.
How to manage SCN pressure
Consider these steps when managing for SCN pressure:
1. Eliminate weeds. Even though you may have rotated your fields from soybeans to a non-host crop, SCN can still survive on winter annual weeds such as henbit and field pennycress. Do a fall or spring burndown, or control weeds with your tillage practice.
2. Select an SCN-resistant soybean variety. Work with your agronomist to find a variety that’s SCN-resistant and will work optimally in your field environment.
3. Include a nematicide as part of your seed treatment. Start control early by applying a seed treatment package to your seed that comes with a nematicide. There are several options available; ask your trusted advisor to pick the one that fits your needs.
4. Rotate soybean acres to an extended non-host crop. For example, you may choose to plant corn-on-corn for a couple of years to try and rotate out of a high SCN situation. Again, if you do rotate the field back to soybeans, choose an SCN-resistant variety or have a nematicide seed treatment applied.
Yield loss can be significant
Remember, SCN can cause up to a 30% yield loss without really ever exhibiting any visual symptoms. That means on a 50-bushel soybean crop, you could have 15 fewer bushels at harvest. So, even though SCN is almost microscopic, its effects can be enormous. Talk with your agronomist about timely soil sampling and ways to help manage this pest.
Zuk is a regional agronomist with WinField United in southern Minnesota. Contact him at firstname.lastname@example.org.