Drift injury to corn and soybean

Although drift problems aren't new in Iowa, increased postemergence applications may result in more problems than in the past. Also of concern is the high biological activity of some new products, therefore increasing the likelihood of drift injury problems. Although drift is not acceptable with any herbicide, special precautions are required for herbicides that may cause injury to non-target plants adjacent to treated fields.

It is also important to recognize that environmental conditions will occasionally cause symptoms that may mimic those seen with some herbicides, particularly the growth regulator herbicides. Generally, injury from herbicide drift will demonstrate a pattern of symptoms; the injury is most severe closest to the source of the drift and diminishes farther away from the treated field. Exceptions to this are when herbicides volatilize and move in the vapor phase, or when the spray droplets are extremely small and environmental conditions allow them to disperse over great distances. In these situations, there may not be a distinct pattern of drift.

This article will provide a brief description of symptoms associated with drift onto corn or soybean of products most likely to cause problems.

1. Growth regulator injury on soybean.
2. Exceed (prosulfuron) injury on soybean.
3. Chlorotic whorl caused by ALS herbicide.
4. Roundup drift injury on corn.
5. Roundup drift injury on corn (closeup).

Growth regulator herbicides: Low levels of dicamba (Banvel, Clarity, Marksman) or 2,4-D can induce significant responses in soybean. Symptoms include leaf cupping, parallel veins, and twisting of stems and leaf petioles (Photo 1). While dicamba is more likely to cause cupping and 2,4-D parallel veins, these symptoms are not always consistent and should not be relied on solely to determine the source of a problem.

Problems with dicamba can arise from either particle drift or vapor drift (volatilization). Clarity contains an amine formulation of dicamba that is less prone to volatilization than dicamba, however, both products are equally prone to particle drift. Clopyralid, found in Stinger, Hornet and Scorpion III, also causes similar symptoms.

Exceed: Soybean is extremely sensitive to prosulfuron, one of the active ingredients in Exceed. Symptoms of Exceed drift are typical of other ALS herbicides, including chlorosis, shortened internodes, and discolored veins on undersides of leaves (Photo 2). At high doses, Exceed may kill the apical bud of soybean.

Lightning: Imazapyr, one of the ingredients in Lightning, may injure corn or soybean if drift occurs. Drift injury will be typical of symptoms caused by other ALS herbicides. Corn may show yellowing of the whorl as occasionally seen following postemergence applications of Exceed, Accent or other ALS products (Photo 3). The Lightning label states not to apply the product in the vicinity of sensitive plants if wind is gusty or exceeds 5 mph and is moving in the direction of sensitive crops.

Roundup: Most people are aware of the sensitivity of corn to glyphosate (Roundup). Symptoms vary depending on dose, crop size, and vigor, but include chlorosis, stunting, and narrow, upright leaves (Photos 4 and 5). One of the most distinct symptoms is the development of white foliage. Roundup drift on corn is more likely to cause lasting injury than most other products.

Predicting the impact of drift on yield potential is difficult because it is impossible to determine the amount of product that contacted the crop. Most drift cases occur early in the growing season, thus the crop has time to recover from the low levels of herbicide typically associated with drift. However, if the plant does not resume normal growth quickly following contact with the herbicide, or if environmental conditions cause additional stress, it is likely that yields will be impacted.

The best way to document the impact of drift on yield is to identify areas within the field that do not appear to be affected. These areas should be identified shortly after the drift event. Comparing yields from these areas to yields from areas of the field that were injured may provide a reasonable estimate of the cost of the early season injury attributable to the drift incident.

This article originally appeared on page 95 of the IC-478(13) -- June 16, 1997 issue.

Updated 06/15/1997 - 1:00pm