Management of Soybean Cyst Nematode uses a six-step approach.
Step 1: Identify the fields that have SCN and monitor populations.
The best time to sample fields for soybean cyst nematode is in the fall after soybeans are harvested as the populations are at their highest. SCN populations can increase as much as 10 to 30 fold per growing season, so early sampling may give lower numbers. SCN is not distributed evenly throughout a field, so it is important to sample in a zig-zag or random pattern throughout the field.
The number of soybean cyst nematode cysts or eggs found in the soil sample will determine the best management plan for the field (Table 1). Techniques for sampling soil for SCN by the Soybean Cyst Nematode Coalition can be found on the Submit a Sample page.
Step 2: Rotate crops. Once SCN has been identified, the best disease management strategy is to keep the numbers low. The best way to keep numbers low is to rotate, rotate, and rotate. Rotating host crops with non-host crops (corn, small grains, and alfalfa) is the most effective method of controlling SCN. Under average Ohio conditions, SCN populations may decline by 50 percent per year under non-host crops. In fields where SCN populations are high, it may take three years or more of non-host crops between soybean crops to reduce SCN populations significantly. It should be noted that nematode populations will not be eliminated in these fields.
If soybeans are repeatedly planted for several years, SCN will again become yield limiting. SCN populations can increase 10 to 30 fold per year on susceptible soybeans. The nematode can also reproduce on many legume crops and weeds, especially purple deadnettle and henbit. These are common winter weeds of no-tillage fields. They emerge from September through early November, and they can increase the SCN population before winter. Therefore, winter annual weeds should be controlled as soon after crop harvest as possible.
Step 3: Use resistant soybean varieties wisely. Resistant varieties should be used in crop rotation with non-host crops to prevent the buildup of soybean cyst nematodes in that field. The resistance that is utilized in commercial soybean varieties does not mean that the soybeans are immune to SCN. Resistance to SCN is characterized as less than 10 percent reproduction on the resistant variety compared to a susceptible variety. Resistant varieties should not be planted in fields with high numbers of nematodes and varieties having the same source of resistance should not be planted repeatedly in the same field. Doing so may select for types of SCN that can reproduce on resistant varieties. Moreover, large numbers of SCN juveniles will puncture and damage roots of resistant varieties even though they cannot reproduce on them, leaving them susceptible to other soil-borne pathogens.
There are currently three major sources of resistance that have been incorporated into commercial varieties: PI88788, Hartwig (PI437654), and Peking. Ohio now has some fields with sizable SCN populations that can reproduce on the soybeans developed with PI88788 source of resistance. PI 88788 is the most commonly used source of resistance, accounting for more than 90% of available resistant commercial varieties.
Step 4: Use best management strategies.
- Fertility—Maintain optimum fertility based on a soil test. Under high SCN populations, even the most fertile fields will be severely affected; fertilization will not eliminate the problem.
- pH—Studies in Wisconsin have shown that soil pH has an effect on the level of yield loss caused by SCN. SCN populations were highest in areas of the field with the highest soil pH (7.1–8.0 vs. 5.8–6.4). Likewise the yield advantage of SCN resistant varieties was greatest in high pH soils and lowest in low pH soils.
- Optimize planting/harvesting dates for the maturity group for your region.
- Optimize drainage for proper plant growth.
Step 5: Manage other diseases. Sudden death syndrome and brown stem rot have been shown to interact with SCN. With SCN many of these diseases can have a larger impact than if the plants were infected separately. Choose varieties that are resistant to these and other Ohio soil-borne pathogens.
Step 6: Prevent introduction. This is the first line of defense. Nematodes can move no more than a few inches a year on their own, so they depend on “hitching rides” on anything that can move soil, such as field machinery, migratory birds, floodwater, or wind. In the past, planting seeds that had not been thoroughly cleaned was probably an important means of moving SCN from field to field. Plant seeds that have been thoroughly cleaned to remove soil particles. SCN can also be introduced into a field by animals, flooding, or wind-blown dust.
HG Types and SCN Types
“HG” stands for the scientific name for SCN, Heterodera glycines. An HG Type is a description of an SCN population that is able to develop and reproduce on a resistant soybean line. The number or numbers in the HG Type designation correspond directly to sources of resistance used in available SCN-resistant soybean varieties as seen in the table below. HG Type applies to the nematode not the soybean. For example, HG Type 0 will not attack any source of resistance, HG Type 2 will only reproduce on PI8788, and HG Type 1,4 will only reproduce on Peking and PI437654 (Table 2).
Some states may use an “SCN Type” to quantify which resistance can be deployed in a field, but this test includes only the sources of resistance used in that state. For example, only #1 (PI 548402 or Peking), #2 (PI 88788), and #4 (PI 437654) are used in Ohio. For example, an SCN type of 1 means that the Rf is >10% on Peking, SCN type 2 has an Rf >10% on PI 88788, and an SCN type 1.2 means the Rf is >10% on both sources.