Crop Scene Investigation - 11 What's behind Sam's uneven soybeans?

Monday, March 31, 2008

His beans seemed 'to be struggling to come out of the ground.' What's more, the stand was thin and uneven across much of the field. So what was the cause?

by CLARE KINLIN

One of my favourite times of year will soon be here. That's when the first soybean seedlings begin popping out of the ground and getting a strong, vigorous start on the season.

Last spring, Sam from Stormont County called because he wasn't seeing signs of vigour in his two-week old soybean crop. "My beans look thinner and less uniform than they should," he said. "They seem to be struggling to come out of the ground."

Poor emergence can be caused by any number of things. Weather, disease, insects, weeds and planting depth can all play a role. I'd need more information before I could establish the problem.

I asked Sam to give me some history on the field. "It was corn last year," he said. "We no-tilled soybeans in May just before those rains came through."

"What about your nutrient program?" I asked, knowing that Sam also had a dairy operation.

"We applied manure this spring."

My ears perked up when Sam mentioned adding organic matter to the soil. A suspect immediately came to mind, but I've been an agronomist long enough to know that it doesn't pay to jump to conclusions.

Sam's remark about the weather also got me thinking. The added moisture meant the soybeans sat in the soil longer than they should, which made them vulnerable to a host of potential threats. A number of different soil-borne diseases and insects can reduce stand vigour.

I arrived at the field to see that the crop definitely lacked the aggressive start that I like to see.

As Sam and I walked the field, a couple more clues supported my suspicions. The problem wasn't in patches - the stand was thin and uneven across a large section of the field. The amount of trash was significant as well. Residue from last year's corn crop and organic matter from the manure application had put this field at risk.

I grabbed my shovel and started to dig. Just as I expected, I found hollowed-out cotyledons - the trademark of a destructive pest. I was ready to close this case.

Can you positively identify the pest in Sam's soybeans? 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

Clare Kinlin, CCA, is a Field Agronomist for NK® Brand, Syngenta Seeds. He is based near Prescott.