Crop Scene Investigation - 41: Why did James' field have a line of troubled soybeans?

Thursday, January 3, 2013

by BERNARD TOBIN

It was an early-June day in Glengarry County when Pioneer Hi-Bred agronomist Scott Fife slowly pulled off the road and got out of his truck to take a closer look. "From the road, it was pretty striking," says Fife, who has become one of Crop Scene Investigation's top agronomic sleuths.

What caught Fife's eye was a single row of discoloured soybeans that travelled right down the middle of an 80-acre field. "The strange thing about it was it was one row and it was dead straight all the way down the field."

The crop had reached the third trifoliate stage with plants in the one row showing significant damage. "They were almost white, as if they were bleached," recalls Fife. "They were stunted and pretty short and had a little browning on the leaves." At first glance, he figured herbicide injury was at the root of the problem, but he wondered how only one row in an 80-acre field could be affected.

Fife's next thought was spray overlap. Possibly the row had been sprayed twice and received double the recommended herbicide rate, so causing the damage. To test his hypothesis, he tracked down James, the farmer who had planted the field. James quickly nixed Fife's theory by explaining that the field was planted with glyphosate-tolerant soybeans and it had only been sprayed with glyphosate.

"There's no possible way glyphosate could have caused that damage, even if you sprayed the row three or four times," explains Fife, noting that he also ruled out spray drift – it would be impossible for stray herbicide to injure plants in a single row down the middle of a field.

Fife then thought other factors might have been at play. Maybe there was something wrong with the planter or the seed? But the field was planted with a well-maintained drill at 15-inch spacing and the seed would have been well mixed. If some bad seed was present, there was no way it could all end up in the same row. The damage could have been fertilizer related, but that didn't make sense because the only fertilizer applied to the field was broadcast.

Having ruled out all potential explanations from the 2012 cropping season, Fife then decided to delve into the field's history. James told him the field had been chisel-plowed and cultivated the previous year, and planted with corn. It was sprayed with HalexGT herbicide.

Fife immediately zeroed in on HalexGT.  It's a corn herbicide that's not registered for soybeans; he had seen HalexGT injury in soybeans and the bleaching symptoms are very similar to what he observed in the single row of damaged soybeans.

But Fife couldn't explain why there would be herbicide residue injury from the HalexGT in only one row of the following soybean crop. Half of the mystery was solved when James remembered that the pressure gauge on his 90-foot Hardi pull-type sprayer had come off during a pass down the field allowing a steady stream of herbicide – many times the recommended rate – to flow from the sprayer. When James turned the tractor at the end of the field the gauge was in full view and he noticed the stream immediately and fixed the problem before re-entering the field for another spray pass.

Obviously, the herbicide residue was significant and it impacted the following soybean crop. But there was one thing that still puzzled Fife. How would a single, narrow band of herbicide so precisely affect one row of soybeans across an entire field the following year? When Fife looked in the cab of James's tractor, the final piece of the puzzle was staring right at him.

Can you explain why the entire soybean row had been so precisely damaged by the herbicide residue?

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. BF