Issue No. 19, Article 4/July 30, 2004
SCN May Be Causing Damage Greater than Expected in Southern Illinois
Soybean cyst nematode (SCN) has been around in southern Illinois so long that many producers are ho-hum about it. It's probably time for soybean growers who know they have SCN to start questioning their complacency.
Jason Bond, a nematologist at Southern Illinois University at Carbondale, collected soil samples from soybean fields throughout southern Illinois. Seventy percent of the samples were positive for SCN, with an average population density of 9,438 eggs per 100 cc soil. This level of infestation is high enough to cause significant yield loss even in resistant varieties.
Field of resistant soybean in southern Illinois showing damage due to SCN. (Photo by Jason Bond.)
We were curious about the ability of these SCN populations to infect resistant varieties, so the samples were tested here in Urbana for their Illinois SCN type. There are three types we worry about:
- SCN Type 1 is able to attack the soybean line Peking (also called PI548402) and any varieties whose resistance comes from Peking. These varieties are not common and represent only a small percentage of the resistant varieties used in southern Illinois.
- SCN Type 2 is able to attack the soybean line PI88788, which is the source of SCN resistance in more than 90% of the resistant varieties grown in Illinois. This type is of greatest concern to us because it limits the choices of resistant varieties available to growers.
- SCN Type 4 is able to attack the soybean line PI437654, which is the source of resistance in CystX lines as well as the public varieties Hartwig and Ina.
We found that 82% of the SCN populations surveyed were Type 1.2 or 2. Type 1.2 can attack both Peking and PI88788, while Type 2 attacks only PI88788. These populations are also capable of reducing yields of resistant varieties carrying either type of resistance, depending on the number of eggs present.
In addition, 36% of the SCN populations surveyed were able to infect PI437654, the source of resistance in CystX and other highly resistant soybean. These infections were at low levels, but they demonstrate that Illinois SCN populations possess the ability to attack this source of resistance and possibly build up over time.
To limit losses due to SCN, producers should recognize that not all resistant varieties are equally resistant. Check out the levels of resistance we found at http://www.vipsoybeans.org.
To reduce losses due to SCN, take these steps:
- Rotate with a nonhost (such as corn).
- Rotate with resistant varieties. Choose the highest yielding varieties with the highest levels of resistance by checking out the VIPS database. Our data in 2003 showed that the correct choice meant an average of $100 an acre to the grower.
- Rotate resistance. Don't grow the same resistant variety twice in a row--even with corn in between.
- Have your soil tested for SCN periodically even if resistant varieties are being grown.