Careless burndown herbicide applications this spring are being blamed for the destruction of thousands of acres of corn in some areas of the Mid-South. Most of the drift problems were apparently caused by off-target movement of burndown treatments using glyphosate herbicides for preplant weed control in cotton and soybean fields.
“The wet spring weather has kept ground rigs out of fields and growers have been forced to use airplanes to make burndown herbicide treatments,” says weed specialist Steve Kelly at the LSU AgCenter's Scott Research and Extension Center in Winnsboro, La.
Kelly estimates that approximately 4,000 acres of corn have been affected by off-target drift as of the third week of April. “A substantial amount of Louisiana's earlier-planted corn emerged quickly, and unfortunately, was killed or severely stunted by herbicide drift. The complaints, for the most part though, are isolated to a few aerial applicators,” he says.
Although the number of drift complaints so far aren't quite as numerous as he had earlier feared, Kelly says he's afraid the complaints are just now starting to be reported. Increasing acreage of herbicide-tolerant crops could also raise the potential for crop injury from herbicide drift later this season.
Corn is the crop most susceptible to this type of drift injury. Just a little whiff of glyphosate devastates small corn plants, crop specialists say. In some cases, glyphosate drift has been tracked up to 1.5 miles from application sites.
While most of the drift-affected fields will have to be replanted, Kelly says some growers are continuing production on the fields despite the likelihood of a yield reduction. “The potential yield reduction will be highest for the portion of the corn crop that was in the five- to six-leaf stage when it was hit.
“The bottom line is if the wind is blowing and you've got a lot of little corn in the area, you've got to be careful with glyphosate,” says Walter Morrison, an agronomist with the Louisiana State University Agricultural Center in Baton Rouge, La.
Research has shown that you may not see symptoms of drift, but you may still experience significant yield loss.
The drift problem apparently isn't as severe in Mississippi where a ban on the aerial application of some burndown herbicides has been in effect for much of the 2002 growing season.
According to the Mississippi Department of Agriculture's Bureau of Plant Industry, burndown herbicides containing the active ingredient glyphosate, sulfosate and/or paraquat may not be applied by air without a permit during the mandated period of time. The ban is similar to one imposed in 2001, except for the addition of two different initiation dates, which are based on geographical location. Applications in both regions are restricted until April 30.
Similar to the 2001 ban, the 2002 burndown regulations maintain a provision for emergency exemptions granted by authorized Bureau of Plant Industry employees within the ban period. Provided when adverse conditions make ground application “impractical or unreasonable,” 72-hour emergency exception permits are made on a case-by-case basis based on, among other factors, adjacent crops and weather conditions.