Crop Scene Investigation - 15: What caused wilted patches in Paul's soybeans?

Sunday, January 4, 2009

By DEB CAMPBELL

Even ideal growing conditions can pose challenges to soybean production. That's why I wasn't surprised when Paul, a grower in Grey County, called saying that there was trouble in his beans. "Patches of plants throughout the field are wilting, drying down and turning brown," he said. "Can you come and check it out?"
It was the first week of August and the entire field should have still been green and growing.

The symptoms were obvious when I arrived in my truck later that day. You could easily see the wilting patches from the road and the damage was even more extensive along the tree lines.  

Paul and I talked about his crop rotation. It had been corn last year and edible beans the year before that. He had used conventional tillage and had mouldboard plowed after both crops.

Once in the field, I got a better handle on the severity of the problem. There were several half-acre patches of damage with 40 to 50 per cent of the plants in each patch wilting and lodging. As with the areas protected by trees, the damage was worse in the hollows of the field. 

Paul and I talked about soil fertility. The farm had been in grain crop production for five years, but prior to that it was a hog farm. This meant that the field would have high soil fertility, which is great for yield, but it can also increase the risk of a number of pests.

My suspicions were that the weather had a hand in this situation, too. The field received extensive amounts of rainfall in July during the early flowering stages of the crop. Paul's drainage system couldn't handle this excess moisture. The farm is randomly tiled and is not systematically drained.
Moisture had definitely contributed to this problem.

I wondered about soil-borne root rots, which thrive in wet conditions, and asked if he had used a seed treatment to protect his seed. "Yes, we used one with a combination of insecticide and fungicide," said Paul. The seed treatment would greatly limit the chance of root rots, but I'd need to check before I ruled it out.

As we were walking through the field, it was evident that the soybean crop was very thick. This was due to a combination of good growing conditions and the fact that Paul had planted narrow rows with a population on the upper end of the seeding rate. Upon opening up the canopy, we could clearly see symptoms on the soybean stems. There were three- to four-inch lesions at the base of the stems that were turning a lighter colour. In some cases, there was a white, cotton-like growth.

The excellent growing conditions that had given Paul these lush canopies had created the perfect conditions for this yield robber.

Can you positively identify what happened with Paul'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

Deb Campbell, CCA, is a Field Agronomist for NK® Brand, Syngenta Seeds. She is based near Dundalk.