'Scared for wheat' with potential herbicide carryover
Farmers take heed if you’re considering planting wheat, oats, or other crops to take advantage of the nitrogen remaining in your fields.
Published: Sep 4, 2012
The dry weather and growing conditions that allowed the nitrogen to be available also may have left soil-residual herbicides.
“I’m scared for wheat,” Barry Nash, a weed science technical manager with GROWMARK Inc., told FarmWeek last week. “My No. 1 concern is wheat, especially in Southern Illinois. Those guys are considering (planting) wheat.”
Nash and others apply a rule-of-thumb that 15 inches of rain between April and November are needed to break down herbicides sufficiently. “There are several areas that have not had six inches (of rain) since April,” he added.
Farmers who plant this fall into fields with herbicide carryover may not see the damage now, but may next year, Nash said.
GROWMARK is encouraging crop advisers and farmers to do simple field bioassay tests to determine possible carryover problems, according to Nash.
He recommended using a spade or trowel to collect soil samples from the top three inches in a field. “I guarantee the herbicide would be in the top three inches,” he said.
For each field, he suggested collecting representative samples for a soil composite of the general field and of possible application overlap areas, such as end rows and point rows. In addition, a bioassay test should be done on a “control” soil composite from a fence row or another place where no herbicides were applied.
For the general field soil composite, Nash suggested collecting soil samples in a zigzag or X pattern across a field.
Place each soil composite in a two-inch deep roasting aluminum pan and water the soil for three to five days, making sure the soil stays moist, he said.
About one week after the sample has been watered, plant the intended crop, and then evaluate the plants for any herbicide injury two or three weeks later.
University of Illinois weed scientists are conducting field bioassays at the Brownstown Agronomy Research Center in Fayette County and the Orr Agricultural Research Center near Perry in Pike County.
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