Crop Scene Investigation - 50: What caused Roman's soybeans to struggle?
Monday, February 3, 2014
by BERNARD TOBIN
One of the things that makes glyphosate-tolerant (GT) crop technology attractive to farmers is its simplicity. If you spray glyphosate on the crop at the right rate and timing, you will get good weed control without injury.
That's exactly what Roman, a Niagara Region farmer, was expecting with his soybean crop last spring. But when he returned a couple of days after spraying to inspect a 50-acre field of GT soybeans, he was shocked to see the crop struggling in the early summer sunshine. Across the field, the plants' new leaves were severely cupped and crinkled, and the stems and petioles were noticeably twisted.
Roman needed some help so he decided to call Syngenta agronomist Shawn Brenneman. "As we talked, Roman explained he had planted 1,000 acres of corn and soybeans, and everything was doing well except for this one field," recalls Brenneman. "When I visited the field, the beans were at the third trifoliate and it was obvious they had suffered some kind of spray injury."
Brenneman's first task was to run through a series of questions on field history that would help him get to the root of the problem. He discovered that Roman maintained a consistent corn-soy-wheat rotation and there was no evidence of herbicide carryover or residual issues.
The scope of damage also ruled out drift or potential problems relating to herbicide residue in the sprayer line or end caps that can typically produce patterns of damage across a field. In this case, Roman's soybeans displayed the same symptoms consistently across the entire field.
"It was classic hormonal injury that you might see from plant growth regulators like dicamba," says Brenneman. Roman had finished up spraying his corn before moving on to soybeans. When Brenneman asked what he had sprayed on his corn, Roman noted that he was using dicamba to control some tough weeds, including glyphosate-resistant fleabane.
Brenneman was pleased when he asked Roman about his sprayer clean-out program. "It was obvious that he followed best management practices, because he cleaned the tank with soap and water and flushed before he moved to soybeans."
Roman also told the agronomist that he had sprayed 200 acres of GT soybeans before he entered the field that sustained injury. "There was no obvious answer, so we really needed to dig into Roman's records," recalls Brenneman. "Something had to have changed before he pulled into that field."
When he examined his log, Roman told Brenneman that he had filled the sprayer with glyphosate and had finished two fields, but then rain forced him to quit before he could use all the spray in the tank.
"He told me they had an inch of rain and had parked the sprayer for three days. When things dried out, they just carried on and moved into the next soybean field. There was just enough product in the tank to finish the field that sustained the injury," says Brenneman. "That's the information that solved the puzzle."
Do you know what caused the injury to Roman's soybean field? Send your solution 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.
For only the second time in the history of CSI readers were stumped by last month's (January's) column. It's not too late to send along your solution for that puzzle as well. BF