Gauntlet carryover

Growers have expressed some concern about alleged Gauntlet carryover to corn planted in rotation with soybean. Gauntlet is marketed by FMC and consists of two herbicides: sulfentrazone, a herbicide in the aryl triazinone family, and chloransulam-methyl, which is in the sulfonanilide family.

ALS inhibitor herbicide injury to corn roots.

Sulfentrazone, also in Command Xtra, Canopy XL, Spartan, and Authority, works on sensitive plants by causing the degradation of cell membranes, resulting in the rapid necrosis of tissue and death of plants. Sulfentrazone has considerable soil residual, but corn demonstrates good tolerance to sulfentrazone. When injury has been observed in corn from sulfentrazone, symptoms have typically been short-lived.

Chloransulam-methyl, a herbicide included in FirstRate and FrontRow, inhibits the ALS enzyme in sensitive plants and may be long-lived in the soil. Symptoms to corn include stunting, poor root formation, "bottle brushed" or stunted root hairs, discoloration of plants, and shortened internodes. These symptoms are similar to those observed when other ALS inhibitor herbicides carryover and cause injury to corn. Typically, symptoms are short-lived but can persist depending on several factors.

Recent field visits by Iowa State University Extension suggest that the injury found in corn following soybean treated with Gauntlet is probably attributable to chloransulam-methyl carryover. There are several factors that contribute to the injury. Notably, application timing and precision (i.e., higher rates due to overlaps) were factors in many fields. Also, the dry conditions that were experienced in 2001 and early 2002 probably lessened the microbial degradation of the chlroansulam-methyl. Furthermore, many fields were treated post with FirstRate, as spot applications where the control of the application rate was suspect or broadcast, which would contribute to the problem. Corn that was treated with other ALS inhibitor herbicides this year could interact with the chloransulam-methyl, resulting in greater injury than anticipated from either individual herbicide.

In many plants, the injury observed early in the development of the corn has dissipated. However, plants that continue to demonstrate injury due to the carryover at this time have little likelihood of recovery. Iowa State University is continuing to investigate these situations and as information becomes available, it will be included in future articles.

This article originally appeared on pages 126-127 of the IC-488(15) -- July 1, 2002 issue.

Updated 06/30/2002 - 1:00pm