Aim Herbicide Injury to Corn

June 9, 2000
During the past weeks, we have received several plant samples and inquiries relating to corn injury from Aim. In a number of these instances, the corn injury appears to be very severe. While it is not completely clear why this severe corn injury is occurring this year, the topic deserves some discussion.

Aim (carfentrazone) is a relatively new postemergence corn herbicide that was first registered for the 1999 growing season. The widespread popularity of Aim this year is probably due to its relatively low cost and effectiveness on velvetleaf. Aim controls susceptible plants by inhibiting protoporphyrinogen oxidase (PPO), similar to other PPO herbicides (Authority, Blazer, Flexstar, etc.). The most common injury symptoms consist of tissue chlorosis and necrosis, which are frequently evident within hours following application.

This "burning" symptomology is caused by rapid damage to plant cell membranes, causing leakage of cellular contents.

The University of Illinois and other universities throughout the north-central region have conducted research over the past 5 years on Aim's weed-control efficacy and crop tolerance. Aim has consistently shown corn injury ranging between 0 and 30% following postemergence applications. The symptoms most commonly associated with this injury were necrotic lesions and in some cases breakage of the leaf midrib.

These symptoms were generally present within a few days after application and usually were not evident 30 days after
application.

How is the injury this year different from injury observed in previous research? Several samples we have received this year have not only shown the typical leaf "burning" symptoms but also a tight wrapping of the uppermost leaves.

In some cases, the corn plants may be able to outgrow this "buggy whipping." However, there are a number of fields and samples that we have seen that probably will not outgrow this injury.

While it is unclear what factors caused this severe injury, it is speculated that applications to wet corn foliage, either from a dew or from precipitation shortly after application, may have concentrated the herbicide into the whorl. By concentrating the herbicide in the whorl, the corn plant may not have been able to metabolize the herbicide quickly enough, resulting in the severe injury and leaf wrapping. Other factors that may increase corn injury from Aim include applying Aim with a crop oil concentrate (COC) to corn not under dry conditions, tank-mixing Aim with an EC-formulated herbicide, and applying Aim during environmental extremes.--Christy Sprague and Aaron Hager

Author: Aaron Hager Christy Sprague