Crop Scene Investigation - 42: How did those devious dandelions get into a Perth winter wheat field?

Tuesday, February 5, 2013

by BERNARD TOBIN

In this edition of Crop Scene Investigation, Ontario Ministry of Agriculture, Food and Rural Affairs weed specialist Mike Cowbrough shares his diagnosis of how these devious dandelions (see photo to the right) managed to find a home in a Perth County winter wheat field last summer.

According to Cowbrough, there are two likely scenarios that could best explain what happened in the field. "The first one is a no-brainer. It has to be a spray miss," he says. "The farmer probably ran out of glyphosate with just a few hundred feet to go and couldn't convince himself to go back and put more spray in the tank."

Cowbrough feels the farmer likely decided the field looked pretty clean and any weeds that emerged wouldn't be very noticeable. "The ground always looks best after soybean harvest, but it doesn't take long for what's hiding under the canopy of the soybean crop to rear its ugly head.

"There's always more there than the eye can see," he explains. "Dandelions don't look that bad after you have gone through with the combine or the drill and they are buried up. You may go out in the fall and see these dandelion rosettes just poking through and feel you don't have anything to worry about."

But, when spring arrives, the picture can look very different. "When there's a clear pattern, as you see in this field, it's either something in the spray tank or a tillage issue. Tillage will get rid of dandelion, but there was no tillage in this field."

Cowbrough says farmers have to be careful not to be too fine when estimating their herbicide needs. "There's a delicate balance between having enough product and running out. Typically, you are going to end up with anywhere from two to 10 per cent overlap, so if you're heading out to spray a field, you want to put 10 per cent more than you need in the tank."

Cowbrough points out that the farmer had more than one opportunity to control the dandelions. The first chance was missed when the spray ran out prematurely. But there was another opportunity to eliminate the escape in late April when the winter wheat crop, which was under-seeded with red clover, also contained a number of winter and summer annual weeds.

To address the newly germinated weeds, and the dandelion miss from the fall, the grower sprayed the wheat with MCPA Sodium herbicide, a selective weed killer that would provide good control of winter and summer annual weeds, but not harm the under-seeded red clover.

But that wasn't good enough to stamp out the hard-to-miss dandelion escape. Do you know why? Send your solution, along with your name, address and telephone number, 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