Soybean Cyst Nematode:
March 30, 2009
“Soybean Cyst Nematode, which is the most important soybean disease in the United States, is a potential concern for dry bean growers.” Speaking frankly to a crowd of approximately 500 producers who attended Bean Day in January, Dr. Berlin Nelson, Department of Plant Pathology, NDSU, told the audience that he has a new potential problem for dry bean growers.
“Soybean Cyst Nematode (SCN) is a root parasite which can reduce dry bean yields. This is a pathogen that can attack the root of dry beans. It is in the Red River Valley and it will move north. It is just a matter of time until it gets into the dry bean growing areas in this region,” said Nelson.
Effect of soybean cyst nematode (SCN) on growth of pinto bean. Plant on the left is growing in soil without SCN and the plant on the right is growing in soil with 10,000 SCN eggs/100 cc soil. (Notice the stunting of the plant on the right compared to the healthy plant on the left.)
SCN, or Heterodera glycines, is one of the most destructive pests affecting soybeans in the United States as well as in the other top ten soybean-producing countries of the world. SCN is a small worm that lives in the soil. The eggs survive in the body of the dead female, called the cyst. It has a very high reproductive capability; it produces a lot of eggs. That is a very important component of disease development. Nelson presented slides of larvae in soybean roots, but stressed, “the same thing will happen in dry beans.”
Nelson and his team at NDSU began to look at this problem from the perspective of all of the crops grown in North Dakota, how would they fit into the rotations with soybeans and the affect of these crops on SCN on these crops. Nelson currently knows SCN is present in Richland, Cass, Clay, Wilkin and Otter Tail Counties. He stressed to the crowd that it is not widespread in those counties; it is only showing up in certain areas. “But the fact of the matter is that it is here. It moves easily from field to field. Once it gets in the dry bean areas, you the growers are going to have to deal with it.”
SCN has the potential to do dramatic damage. Nelson said, “We can control it in soybeans with two primary methods, 1) the use of resistant cultivars and 2) the use of crop rotation. These two management strategies are essential to managing SCN.”
What effect will SCN have on dry beans?
Scientists have known for over 80 years that SCN can attack soybeans but there has been almost no research what so ever on the effect of SCN on dry beans, mostly because in most soybean areas you don’t have big dry bean production. This is a concern for Nelson. Dr. Rubella Goswami, a dry bean pathologist at NDSU, is also concerned about the interaction between SCN and root rot fungi that could increase damage to the roots. She and Nelson are cooperating to find out if this is another potential problem associated with SCN.
A few years ago, Nelson started to look at dry bean groups in this area to find out if SCN reproduced on those groups. “When we compared the reproduction of SCN under a controlled test, this nematode reproduced just as good on the kidney bean plant as it did on soybean plants. When testing the black bean cultivars, they appear to have some resistance. Working with the pinto and navy bean cultivars, the nematode did not reproduce as well as on soybeans, but it still reproduced. “We think it reproduces enough to cause some potential problems in your fields,” says Nelson.
We know SCN is reproducing in the fields, we know it is producing eggs and we know the eggs are pathogenic on dry beans. We have done all that research. We have done several studies in 2008 and we have seen the same things as in trials in 2007. Both the growth and yields are being affected.
Steps to Lower Your Risk of SCN
There are ways to lower your risk of SCN. A grower can have SCN in dry beans and not notice damage. How are you going to prevent the damage? Nelson says, “If you have reports of SCN in your area, and you are concerned about it in your field, gather a sample of your soil, send it to a qualified laboratory and find out if you have SCN. If they come back with a report that says you have a low eggs count, you should be concerned about those numbers, and the best thing to do is that if you grow a dry bean you want to come back next year and sample the soil again and get those eggs numbers again to find out what is happening in your fields. Rotations will help reduce those numbers but unfortunately in our area, we know those egg numbers, especially if they get high, persist a long time in the soil.” Nelson went on to say, “We can’t stress this enough: Don’t let the egg numbers get too high because it is very hard to bring them down again. If you grow kidney beans, be aware of this. The fact is that our tests show it can reproduce very well on kidney beans.”
Not all is hopeless, however. Nelson provided examples of how to prevent damage from SCN in dry beans:
- Find out if you have SCN in your fields. Sample the soil and have the samples processed by a qualified laboratory. They will tell you the number of eggs per 100 cc of soil.
- Consider longer rotation to non-host crops to reduce egg levels. Consider keeping dry beans off the infested fields.
- Minimize soil movement between infested and non infested fields.
- Monitor the egg levels to watch for increases in egg numbers. Higher egg numbers will result in more damage.
- If you grow kidney beans, be especially aware of potential damage.
- Bean types and cultivars differ in susceptibility to SCN.
- Sandy loam soils will be more likely to have SCN damage than heavy clay soil.
- Dry years will likely increase disease damage.
- Bean seed is often treated with an insecticide. As yet we do not know how much control that will provide to the plant. More research needed on this potential problem.
Nelson is a professor of Plant Pathology at NDSU where he has been conducting research on field crop diseases for 30 years.
Summary of what Nelson knows about SCN and dry beans
- Dry bean yields can be reduced by SCN
- SCN reproduces on dry bean in the field and will add eggs to the soil
- Egg density associated with yield loss in pinto and navy bean will probably be higher than with soybean.
- Some cultivars are possibly tolerant of SCN damage, but more research is needed.
- It is important to remember that you can have SCN in dry beans and not notice the damage by looking at plants.
- The nematode is extremely easily moved from field to field, traveling long distances because it will travel in the soil particles.