Crop Scene Investigation - 60: Brittle soybeans take a tumble

Tuesday, February 9, 2016

by BERNARD TOBIN

Sean Cochrane had never seen anything like it. The eastern Ontario-based DeKalb agronomist has walked lots of fields in his career, but he's never witnessed anything like he observed in a 40-acre soybean field last August, near Tweed, Ontario.

"I was the third guy on the scene," recalls Cochrane. "It wasn't one of our varieties but the seed retailer was having a tough time figuring out what was going on and asked me to take a look."

The field was planted mid-May with a conventional soybean variety into cool, wet planting conditions. When Cochrane arrived the plants were in the R6 stage. From his vantage point, the field looked pretty average, but his perception changed abruptly when he stepped into the field. "As you walked, every time you brushed against a plant, your could hear it snap off. I was quite astounded. The stems had absolutely no flexibility."

When Cochrane picked up the broken plants he couldn't believe how brittle the stems were. "They broke off right at the soil surface. At the breaking point the stems were swollen and there was also a very visible canker."

Disease was the first possible cause that came to Cochrane's mind, but he quickly ruled out the usual suspects. "We didn't see the typical brown discolouration that you see on the stem with brown stem rot." He also eliminated phytophthora root rot: "it typically makes plants quite rubbery and flexible, and that certainly wasn't the case in this field."

When Cochrane split the stem he noted the plant appeared to be quite normal. They were the right colour and appeared to be fairly healthy. It was then time to look below ground. Maybe the roots would tell the story. But that theory came up empty. What he found were normal, well-developed roots with no sign of disease.

It was indeed a head scratcher. There were no variations in plant height across the field and their appeared to be no soil compaction. "The fact that it was throughout the field was a confusing part," notes Cochrane. "Diseases tend to express themselves in circles and waves in fields. Human interaction tends to express itself in lines and squares. But the brittle stalks were throughout the field so we really couldn't determine a pattern. There were no areas of the field unaffected."

Cochrane still had a few possible explanations. The problems could be herbicide related, possibly a residue-carryover issue or a fertility problem, but both of these were dead-ends. The field had a short but reasonable corn-soy-corn-soy rotation, good fertility, and the herbicide program checked out – no issues.

The farmer was convinced that the right thing to do was to chop the crop for silage rather than stand as the stalks cracked and fell over. But Cochrane thought the farmer should hang in there. Maybe the crop would stand long enough to see the combine. That would also give Cochrane some time to do some research to discover what would make soybean plant so fragile and brittle that it would snap at the base with a simple touch.

Do you have any answers for Sean Cochrane? Send your solution along with your complete contact information to Better Farming at: rirwin@betterfarming.com or by fax to: 613-678-5993.    

Correct answers will be pooled and one winner will be drawn for a chance to win a Wireless Weather Station. The correct answer, along with the reasoning followed to reach it, will appear in the next issue of Better Farming. BF