As part of a multi-state, 3-year North Central Soybean Research Program project, we have compared the changes in SCN populations under varieties which are susceptible or have resistance derived from PI 88788, Peking, or PI437654 (CystX). Management of soybean cyst nematode consists primarily of crop rotation both with non-hosts and with different sources of resistance (if they are available).
|Best SCN Management Strategies for Ohio Soybean Producers|
|Egg counts/200 cc of soil||Cyst Count||Population Level||Management Strategies|
|0-40||0||None detected||Continue to monitor field after two crops of soybean|
|40-200||1||Trace||Begin to measure some yield loss in Susceptible varieties at or above 200 eggs/200cc|
|200-2000||1-4||Low||Plant SCN resistant variety or rotate to a non-host crop. At or above 2000 eggs some yield loss may occur on SCN resistant varieties|
|2000-5000||3-20||Moderate||Rotate to a non-host crop next year and return with SCN resistant soybeans the following year.|
|5000 and over||15-20 and higher||High||Rotate to a non-host crop for two to three years then sample the soil to determine nematode populations before planting SCN resistant varieties|
This study was planted in 9 locations over the past 3 years, each with a different initial SCN population. At each location, five soybean varieties were planted in randomized block design with four replications. Each variety strip was sampled within a few days of planting in the spring and again after harvest. For each strip, 6 to 10 subsamples were collected. The average egg counts are the mean of the subsamples. On average there were 200 SCN samples collected from each location at each sampling. The yields from each strip were collected by the producer/educator cooperator and adjusted to 13.5% moisture.
The table below has the yields for each of the different varieties derived from the different sources of SCN resistance.
|Type of resistance||San08||Put08||San09||Put09||She09||Put10||Pik10||Ros10||San10|
|*** indicates that P value was <0.001|
|** indicates P value was <0.01|
|* indicates P value was <0.05|
|Note: Yield difference in 09-Putnam maybe due to Phytophthora partial resistance levels; 10-Ross and 10-Pickaway these yield difference were due to shattering of the earlier lines.|
One of the nine locations had significant yield loss (approximately 50%) when SCN populations were greater than 3,000 eggs/cup of soil. When SCN populations were 200 to 500, yield loss occurred (Sandusky 09) but not in Putnam08. This may be due to the fact that the Putnam location had a very uneven distribution of SCN in the field. At this location in the spring, 23% of the subsamples SCN was not detected. When SCN populations were less than 200, the differences in yield were not significant (ns) or could be attributed to other factors, shattering of early maturing lines, lack of Phytophthora resistance
The SCN populations changed in density under each type of resistance at location, the Sandusky 2009 location was a bit of a “hot-spot” and had dramatic increases in SCN numbers under the susceptible as well as all of the sources of resistance.
|Resistant Source||Spring||Fall||fold change|
The remaining locations, had either an increase (Shelby09, Putnam10) or decline (Putnam08, Sandusky08).
The take-home message from all of this is caution, SCN numbers can increase dramatically when susceptible or even resistant varieties are grown and it is going to be critical to continue to monitor SCN numbers as part of the basic soybean production practice or management program for Ohio. In most cases when resistant varieties were planted the SCN numbers declined. However there were several fields where this did not happen. The higher the SCN numbers, the less likely that egg counts dropped even under the resistant varieties. Bottom line: keep the SCN populations low through rotation.
Ohio has evaluated soybean varieties, each with different types of SCN resistance, for the past 3 production seasons. In addition to documenting the dramatic changes that can occur in SCN populations, other key findings from this study were:
Our original recommendations based on egg counts are correct across the soil types.
Identified SCN populations in which the PI88788 is not as effective as it once was.
Demonstrated that varieties with SCN resistance yield as well as those with no resistance when SCN populations are <200 eggs/cup of soil
Varieties with SCN resistance out yield susceptible varieties when SCN populations are high.
The highest yield loss recorded in the susceptible variety was close to 50% in the first year of the study when populations were very high.
For additional information about SCN Management, the NCSRP funded Plant Health Initiative has a very nice website including videos with collaborator Greg Tylka (Iowa State University) about soil sampling (http://www.planthealth.info/scn_basics.htm)
For more Ohio information and a listing of labs that do soil analysis for SCN see our factsheet at: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/soybeans/AC_39_08.pdf
These studies were part of a multi-state project and we are still processing soil and waiting for the HG-type data from our collaborator. We want to thank the producers that participated in this study, without their outstanding assistance this would not have been possible.