This past year, more fields in Ohio had soybeans that developed symptoms of sudden death syndrome (SDS) than in any year previously.

In addition, these symptoms were widespread across the state. At this time probably close to a 1 million acres maybe affected. In addition, soybean cyst nematode (SCN) is also prevalent in many areas of the state – almost all of Ohio’s soybean fields have some level of infestation and it continues to increase in numbers as rotations with other crops are reduced.

There are no clear-cut symptoms of SCN. In only a rare case will plants be stunted and yellow – but in these cases the populations are off the charts and the field maybe lost for some time for profitable soybean production. It is kind of like having a teenager in the house. You know you just got cash from the ATM, but it just doesn’t stay in your wallet and you don’t have any idea where it went –except for fast food most likely – maybe a movie for your teenager. I don’t know what movies soybean cyst nematode would watch – but they do eat – and soybean could be considered the “fast food”! Previous studies in Ohio compared yield losses from a highly resistant line to a susceptible line and showed that yield losses to the tune of 10 to 15 bushels with populations ranging from 8,000 to 10,000 cysts/cup of soil.

SDS has beautiful symptoms – there is no denying it. Just about the time producers and consultants are taking those last yield assessments, the foliar symptoms begin. Bright, bright yellow spots which turn brown (necrotic) – and the necrotic areas are surrounded by the bright yellow. The leaves will fall off the plants – leaving the petioles behind. The roots are rotted and the tap root is a gray color and the pith is white. In contrast, brown stem rot has a wimpy yellow color and the pith is chocolate brown. There are numerous cases where both diseases can be found on the same plant.

Several studies from Missouri and Purdue have nicely demonstrated that when plants are inoculated with SDS alone symptom development is much, much lower as is yield loss. With SCN and SDS inoculated together, the beginning of symptom development is much earlier and yield losses are more dramatic. Note that the fields where they screen for SDS resistance in Southern Illinois have SCN. Where we inoculate in Ohio (Wooster) – we rarely get good symptom expression, no SCN and we water an inch per week. I am usually pretty good with making susceptible plants sick!

For the fields that had SDS symptoms develop on the soybeans – these fields need to be checked for SCN. SDS is a great indicator that there is a problem. Once the field has been checked for the levels of SCN – then management plans can be put in place for both of these soybean pathogens. First, for next year (2008) plant something different. If you’ve got a problem in a field the best way to stop it from becoming worse is to plant something else.

Then begin the 2009 season with the following plan:

• If SCN Levels are between 200 and 2,000 – a SCN resistant variety may be the best way to go. If SDS was also present, find a variety that is resistant to both, University of Illinois does test for SDS and follow this to the Variety Information for Soybeans Page. This is a sortable link to their database.
• If SCN levels are between 2,000 and 5,000 – plant corn, wheat or alfalfa – all are quite profitable right now and these would be the fields to select.
• If SCN levels are over 5,000 – again you are looking at least 2 years out of soybeans for that field.

During 2007, one field with extensive development of SDS in the soybeans – when checked the SCN populations had hit 10,000 – no stunting or any other apparent symptoms for SCN were present.

Why is SDS more widespread appearance in Ohio?

There may be several reasons for this. One is the switch in the base germplasm over the past 10 years. Williams82 was a predominant variety or crosses with this line were planted widely in Ohio, Williams 82 is resistant to SDS but highly susceptible to white mold. Another feature is early planting. To get the best symptoms in field evaluations, they plant 2 weeks before the normal planting season. The theory is that the cold soils may promote infection, this needs some more study, but Ohio has moved the planting window for soybeans much earlier and this may have contributed to the increase in infections during 2007. Our rotations have gotten much worse. With the exception of 2007 where corn made it onto 4 million acres, there are numerous fields in Ohio that are continuous soybeans. This lack of rotation is also helping build population levels and facilitate the spread of SCN as well.

The management strategies are very similar for both of these soybean pathogens. The key is going to be to monitor SCN population levels and look at the resistance package in the soybean varieties that do get planted in these problem fields. With funding from Ohio Soybean Council, we will be evaluating a greenhouse assay this winter which was developed through check-off dollars to the North Central Research Program. If we can get this to work in our greenhouses, then this could be another addition to Ohio’s Performance trials in the future.

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