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Don’t try this weed strategy at home

One ingredient you probably shouldn’t count on every time in your weed control strategy is luck. Yet here’s an example of what someone can do with modern herbicide technology and, yes, a little luck.

The Indiana Prairie Farmer/Precision Farming plots at Purdue University’s Throckmorton farm last spring were planted May 27 with a Liberty-tolerant hybrid provided by 1st Choice Seeds, Milton. No residual herbicide was applied. The plan was to spray postemergence.

A rainy spell set in. By the time it was practical to spray, most corn was in the V5 to V6 stage. Lambsquarters, giant ragweed, velvetleaf and giant foxtail were racing to see which could get above the corn first.

Key Points

• Wet weather delayed postemergence spray applications.

• Big weeds were tamed with the right herbicides, good conditions and luck.

• Putting residual herbicide down prevents early weed flush.


Jeff Phillips, Tippecanoe County Extension ag educator in charge of the plots, advised Pete Illingworth of the farm crew that he should spray as soon as possible. He made the application July 6 at 5 p.m. He sprayed (all per acre) 22 ounces Ignite, 3 ounces Capreno and 6 ounces Moxy2E. He added 3 quarts of crop oil and 2.5 gallons of Amsol per 100 gallons of water. “I would have liked to spray earlier, but spraying late was better than not spraying at all,” Illingworth says.

What an understatement! By harvest, it was difficult to find a weed. The only foxtail showing was on the outside edges of the previously ponded plots. It was one of those “you have to see it to believe it” moments. Yields went from 99 bushels per acre on the worst ponded plot to roughly 240 bushels per acre.

Lucky roll

Bill Johnson, Purdue weed control specialist, can only shake his head. When asked about other options for dealing with weeds that tall, he quipped, “Prayer, maybe divine intervention. There really is nothing that is good on big weeds. You got lucky.”

The situation can become problematic quickly, he says. By the V8 growth stage, some treatments are off-label. Letting weeds grow that long ties up nitrogen intended for the crop.

Early-season yield losses from weed growth can be severe, Johnson notes. In this case there’s no way to know because there was no check strip where weeds were controlled from planting.

Other options

One option would be starting with a residual herbicide, even if you intended to come back postemergence, Johnson says. A combination with atrazine and an active ingredient for grass control can do a good job.

These include, but aren’t limited to, Dual, Harness, Surpass, Outlook, Basis, Capreno and Balance. Once you’re in a postemergence situation, how you spray matters, Johnson says. Statements on the Liberty label warn against spraying early in the morning or late at night. Some researchers report poor control on broadleaf weeds after spraying glyphosate at night.

When weeds are as out of hand as they were here, Johnson recommends 20 or more gallons per acre of spray volume, with nozzles that create a medium to fine droplet size.

01113440a.tif

Jungle time: Weeds were so thick it was tough to stage growth of plants in these plots.

01113440b.tif

Wow factor! Where did the weeds go? Control was unbelievable.

This article published in the January, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.