CROP SCENE INVESTIGATION - 6
What caused Blake’s soybeans to wilt?

There were patches of unhealthy, drooping plants in this Huron County grower’s fields. The problem wasn’t Sudden Death Syndrome or anything to do with his herbicide and fertilizer programs. So what was it?

Growers have a unique ability to transform into detectives when something’s not right in the field. Many go about diagnosing crop difficulties with confidence. But every now and then I get a call for a second opinion. As an agronomist, I appreciate the chance to team up with a grower to tackle a problem.

I was a willing team mate when Blake, a soybean grower in Huron County, called for support in mid-July. He wanted my thoughts on a puzzling situation. “The crop looks like it’s dying. I have some ideas, but I’d like to get your opinion,” he said.

Blake reported there were patches of wilting plants throughout the field. When I heard the word “patches” I suggested the possibility of Soybean Cyst Nematode (SCN), which appears in this kind of pattern. “I thought about that, too,” said Blake. “I sent a sample away to the lab for testing and it came back negative.”

With SCN ruled out, Blake started looking for other suspects. There was talk amongst his neighbours at the local coffee shop about root rot. But Blake thought it was too dry for that to be the problem. Rainfall was at a record low this summer and farmers everywhere were feeling the effects of drought.

Blake knew that his problem wasn’t simply lack of moisture. We reviewed his herbicide and fertilizer programs and everything appeared to be in order.

Blake was pretty sure the patches of dying soybeans were the victims of Sudden Death Syndrome (SDS). In my experience, SDS is not typically a problem in dry years. It can occur in a drought, but usually only in fields with a history of SDS. I had a feeling that there might be something else going on, so I arranged for a visit to Blake’s farm.
When I arrived in the affected field,
I observed several patches of unhealthy, drooping plants. Upon closer examination, the upper leaves looked scorched, and the stem tips were wilting. Some of the middle and lower leaves were yellowing or had pale yellow spots on them. The stems appeared to be free of any lesions or external decay.

I had a hard time getting my shovel into the ground when I dug out a few soybean plants. “The conditions were really wet when we took the corn off last fall,” said Blake. “We tried our best to fix the ruts with fall plowing and spring tillage.” Blake wasn’t alone in having this problem. I visited many farms this spring with cloddy soils. The soil compaction was definitely contributing to whatever was making Blake’s plants wilt.

After cutting some stems open lengthwise, I noticed that the vascular tissue and pith were a brown colour. A red, orange or white mycelium also appeared in some stems. There seemed to be some purple discoloration on lateral roots as well.

Can you identify what the problem was in Blake's soybean field? Send your solution to Better Farming at: rirwin@betterfarming.com, or by fax to: 613-678-5993.