Crop Sensitivity to Auxin Herbicides

Drs. Stanley Culpepper, J. Smith, and Eric Prostko of the Univ. of Georgia have published scales that indicate the degree of sensitivity of various crops to 2,4-D and dicamba, active ingredient components of auxin-containing herbicides that can be applied to tolerant crops. The ratings are based on the herbicide rate that imparts visually detectable injury. The four categories they have designated are lower sensitivity (> 1/75X), moderate sensitivity (1/75–1/300X), severe sensitivity (1/300–1/800X), and extreme sensitivity (< 1/800X). They based these scales on data from available literature and Univ. of Georgia experiments.

Notice that even the crops that are ranked in the lower sensitivity category still are sensitive to concentrations that are greater than 1/75 of the labeled rate for each herbicide. Thus, all of the shown crops are sensitive to these two auxin herbicides. These ratings really show how even minute amounts of the auxin herbicides that are inadvertently deposited on sensitive crops will result in visual injury.

The bottom line from this sensitivity scale is that auxin herbicides that are inadvertently deposited on non-tolerant plant species will cause injury to those plants. This is not news, but the scale the authors provide is a quantified reinforcement of the need to prevent off-target movement of these herbicides.

Search “auxin herbicides” on this website for additional information pertaining to their use in cropping systems that use crop varieties that are tolerant to them.

Composed by Larry G. Heatherly, Feb. 2017, larryheatherly@bellsouth.net