No. 11/June 5, 1998
Corn Injury Abundant Across Much of Central Illinois
This past week has seen a tremendous increase in the number of phone calls and plant samples received that relate to corn injury symptoms. The causal agent(s) of several injury cases has been fairly obvious, but as was pointed out in the last issue of this Bulletin, some instances tend to have several factors contributing to the observed corn injury. The two most common scenarios have been corn with white foliage and emerged corn with upper leaves failing to unfurl correctly.
"White" corn. Typical symptoms that have been reported include a whitening of leaf tissue near the plant whorl and/or white patches on leaves. The two main herbicide-related causes of white tissue on corn leaves are exposure of the corn plant to clomazone (Command) or glyphosate/glyphosate trimesium (Roundup Ultra/Touchdown). With the limited use of Command in Illinois, the likelihood that most of the corn exhibiting white tissue is affected by carryover of this herbicide is remote. In many reported instances, exposure to Roundup Ultra/Touchdown has been strongly suspected. But how has corn been exposed to these herbicides?
One scenario that has been alluded to on several occasions is that the corn was planted (often no-till, but not always) with no herbicide applied prior to planting. Two to 3 days after planting, the field was sprayed with some herbicide combination including Roundup Ultra or Touchdown. Corn emerged from the soil within 1 to 2 days following the herbicide application and, a few days later, began showing white discoloration of the leaf tissue. If corn actually emerged within 1 to 2 days following the herbicide application, it is highly probable that some part of the coleoptile was exposed or emerging when the herbicide application was made. A very small amount of these herbicides coming into contact with emerging corn can cause the white tissue, which is noticed several days following emergence.
Another means by which corn is exposed to Roundup Ultra/Touchdown is through herbicide drift. Most of the corn crop has emerged, and a significant portion of the soybean crop has yet to be planted. No-till soybean fields, which require a burndown herbicide application prior to planting, are often adjacent to corn fields. When burndown herbicides are applied under windy conditions and drift occurs onto neighboring corn fields, the characteristic white tissue-injury symptoms can develop.
The crop conditions in 1998 are somewhat reminiscent of those in 1996, when there was a large number of drift cases. First, the corn crop has had much less-than-ideal growing conditions for most of the 1998 growing season. The stressful growing conditions may predispose the corn to be more susceptible than normal to herbicide injury. Second, delays in soybean planting have also delayed burndown applications. As delays continued, more corn has emerged close to no-till soybean fields where burndown applications were made. Finally, windspeed can have a substantial influence on how far a herbicide may drift during application. Obviously, higher wind speeds can result in spray solutions moving longer distances.
If corn has been exposed to Roundup Ultra/Touchdown, will it recover from the injury? This question is difficult to answer, as many variables (such as how much herbicide the plant was exposed to and the growing conditions over the next few weeks) will have an influence. If a corn plant produces new leaves that are green as they emerge from the whorl, this plant may have a greater likelihood of surviving than a plant whose leaves emerge white from the whorl.
Emerged corn with upper leaves that fail to unfurl properly. Another commonly reported injury symptom in corn is emerged plants with upper leaves that are tightly wrapped and fail to properly unfurl. Many people refer to this injury symptom as "onion leafing" or "leaf laddering." This type of injury symptom can be caused by the chloroacetamide herbicides. This herbicide family includes products containing acetochlor (Surpass, Harness, TopNotch, and atrazine premixes), dimethenamid (Frontier and Guardsman), metolachlor (Dual II, Dual II Magnum, and atrazine premixes), and alachlor (Lasso, MicroTech, and atrazine premixes). Preemergence applications of growth-regulator herbicides (primarily 2,4-D) also may cause similar symptoms.
A common scenario described with corn plants expressing this type of injury is a preemergence application of one (or a combination of) of these herbicides, followed shortly (within 3 days) by rainfall. Reports of corn with this type of injury are far more common when the interval between herbicide application and planting is shorter rather than longer (for example, if the herbicide was applied several weeks prior to planting). The wet soil conditions across much of Illinois have induced a stress on the corn that may slow the crop's ability to metabolize the herbicide before injury symptoms develop. Keep in mind, however, that not every case reported thus far involves a chloroacetamide herbicide. In research plots, this type of injury can sometimes be observed in plots where no herbicide has been applied, but it is far more frequently encountered in plots where a chloroacetamide herbicide has been applied.
Will the corn recover from this type of injury? Often, corn is able to recover from this type of early season injury. When air temperatures stabilize and soil moisture becomes closer to normal, the corn likely will be able to grow out of this injury.
Aaron Hager (firstname.lastname@example.org) and Marshal McGlamery (mmcglame@ uiuc.edu), Crop Sciences, (217)333-4424