Herbicide injury more common this crop season

Herbicide injury symptoms on corn and soybeans showed up in many fields across Iowa this spring, more so than usual. There was an increased use of preemergence herbicides. Weather conditions during planting season also had a lot to do with increased incidence of crop injury.

Herbicide injury more common this crop season

Herbicide injury symptoms on corn and soybeans showed up in many fields across Iowa this spring, more so than usual. There was an increased use of preemergence herbicides. Weather conditions during planting season also had a lot to do with increased incidence of crop injury.

Farmers have become accustomed to no crop response to herbicides due to the reliance on Roundup Ready crops for the past two decades, so this year was sort of a rude awakening, observes Bob Hartzler, Iowa State University Extension weed management specialist.

“Soil-applied herbicides have been very active this year, resulting in a significant number of cases of crop injury,” he adds. Two factors, he says, are likely responsible for these occurrences:

• spread of herbicide-resistant weeds led to increased use of preemergence herbicides

• stressful environmental conditions following planting

In some situations heavy rain following planting moved the herbicide to the depth of the crop seed resulting in increased absorption of the herbicide, says Hartzler. Below-normal air and soil temperatures reduce a plant’s ability to metabolize or break down the herbicide, increasing the likelihood of the herbicide accumulating at the site of action in the crop plant.

Another factor causing crop injury, he says, is the increasing use of tank mixes with multiple herbicides (cocktails). Using multiple sites of action broadens the spectrum of control and may reduce selection of resistant weed biotypes. However, multiple herbicides can be more difficult for a plant to deal with and increases the likelihood of an undesirable crop response.

Herbicides that rely on differential metabolism for crop tolerance have the potential to cause injury under conditions that stress the crop. “This year’s weather resulted in injury from herbicides that we have considered to have a good margin of safety,” he says. “In most situations, the injury is short-lived, and crops are able to quickly recover with minimal impact on yield potential.”

Herbicide carryover symptoms of fomesafen on corn were common this spring. Fomesafen is the active ingredient in Flexstar, Reflex and a number of other postemergence soybean herbicides. The increase in late-season applications of products containing fomesafen is responsible for this carryover problem.

Many other herbicides also caused crop injury. Hartzler explains three cases of adverse crop response to herbicides with the accompanying photos.

Source: Iowa State University

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seedling injury: Flumioxazin (Valor) and sulfentrazone (Authority) can damage soybean hypocotyls and the apical bud when rains occur at cracking stage. Slow emergence this year prolonged the susceptible period.

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Root of the problem: Bottle brush roots are characteristic of Group 2 (ALS) herbicides. “We’ve seen injury from flumetsulam (SureStart) applications, carryover of chloransulam (FirstRate) and a possible additive response between the two herbicides,” says Hartzler.

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leaves Gone awry: Deformed foliage follows application of Group 14 and 15 herbicides (Fierce, Authority Elite). Interaction between these two groups increases the likelihood of injury, although soybeans usually grow rapidly out of this type of damage.

This article published in the July, 2014 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2014.

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