As fall approaches, two things are certain – winter will come and soybean cyst nematode (SCN) has done its business! For many growers, managing soybean cyst nematode means planting SCN resistance varieties BUT effective SCN management does not end when you have selected your soybean varieties! It is imperative to not only know your SCN population levels in each of your fields but what is happening to those levels over time. If SCN is decreasing, this would indicate your management program is working. If they are rising, it is a red flag indicating the problem is getting worse and could get out of hand, costing you significantly losses in yield, dollars and sleep! If you are unaware of what is happening to the SCN population levels in your fields over time, your efforts may be wasted. One of the most important decisions a producer can make concerning this devastating pest, is to take a SCN soil test.
Soybean fields across the province are quickly turning and harvest has started on some early short season soybeans. Sampling for SCN after or at harvest provides a perfect opportunity to “take the test”. This is typically a time when soil samples are taken to determine next year’s fertilizer program. It is as simple as taking a few more soil cores from the field, mix them together, split the sample and send in half for your fertilizer recommendations and the other half for a SCN analysis. Fall sampling also helps identify poor yielding fields or areas within the field that need sampling while they are fresh in your mind. A fall sample takes into account any significant SCN population changes that have occurred during the growing season.
Remember, the results of the test are only as good as the soil sampling technique. Therefore, it is necessary to obtain a soil sample that is representative of the field. Ideally, the number of acres in any one sample should not exceed 20 – 25 acres. The fewer acres a sample represents, the more accurate the results. Having said that, one large field sample (50-100 acres) is better than no sample at all.
Soil samples should be taken at fixed distances, regardless of the appearance of the crop. Do not concentrate on poor areas of the field unless a whole field sample is also taken. This will allow for a comparison between the poor areas and the whole field. Samples should represent similar cropping history and soil texture within a field.
Using a narrow-bladed shovel, a garden trowel or soil probe collect soil to a depth of 6 – 8 inches in a zig-zagging manner across the rows. Take 15 – 20 subsamples for each 5 – 10 acre area to be sampled. Samples should be collected as close to the old crop as possible preferring soil within the row. As mentioned, the nematode sampling method is the same as a soil fertility sample therefore, both samples could be taken at the same time. Clearly mark that the samples are for a SCN test and they can be sent to any of the SCN testing labs in the province (OMAFRA Agronomy Guide Publication 811 – Appendix E, page 413).
When you get your test back what does it mean?
First it lets you know if you have SCN and what the potential yield loss risk is for the field based on the SCN population levels. If you get a “Not Detected” result this means SCN is not present, is below detectable levels or as often is the case SCN levels are variable in the field and these pockets where not captured in the sampling pattern. It does mean you should continue to monitor these fields since SCN levels can change rapidly. Anything below 1,000 eggs/100 gm of soil is considered low risk with a potential yield loss for susceptible varieties ranging from 0-20 per cent and a resistant variety should be grown or rotate to a non-host crop (corn/wheat). Moderate to high risk fields (1,000 to 10,000 eggs/100 gm soil) potential yield losses range from 20-50 per cent and SCN resistant varieties will likely be impacted especially those containing the PI88788 source of resistance. Fields with over 10,000 eggs/100 gram of soil should be rotated to non-host crops for two years and then sampled again to determine if populations have declined sufficiently for soybeans. A susceptible variety will see significant yield losses as well as those containing the adapted PI88788 population (SCN Type 2).
SCN continues to build and spread in the province, highlighted by the recent confirmations in Simcoe county. Last week, Manitoba joined Ontario and Quebec as the only provinces in Canada with known SCN infestations. The earlier SCN is identified in your field, the sooner management practices can be initiated to limit SCN reproduction and keep populations from reaching economic injury levels. Management practices such as crop rotation with resistant varieties, rotation of SCN resistant sources PI88788/Peking, the use of non-host crops such as corn/wheat, using new seed treatment nematicides will help maximize crop yields, minimize economic losses as well as reduce the incidence of sudden death syndrome and several other soybean diseases.
Although SCN cannot be eliminated it can be beaten. The first step is identification, so get out there and sample. Take the test and beat the pest! Know your number!