Crops and Soils News Column – Dicamba Label Change Impacts

Josh Coltrain

Crop Production and Local Foods Agent

Wildcat Extension District


Dicamba has dominated the cropping systems headlines for much of the past year or even more. After one year of use, the Environmental Protection Agency (EPA) made some adjustments to the new product labels in mid-October which could impact the use of the herbicides, maybe more so than initial reactions.

Some of the changes include reclassifying the products as restricted-use herbicides. Like all restricted-use chemicals, a pesticide license (private or commercial) will now be required to purchase the chemicals. In addition to the traditional certification, an additional dicamba or auxin-specific training will be required. Unfortunately, how this portion of the new regulations will be carried out remains to be seen.

Additional record-keeping will be required to use these products as well. In fact, the records are quite substantial and must be kept for two years after application. Amongst other standard record items like “Product name” and “EPA registration number” are items like “Sensitive Crops Awareness” and “Training Requirement.” The sensitive crops awareness is intended to show that the applicator has checked appropriate sensitive crop registries and surveyed neighboring fields for any sensitive areas.

New restrictions have lowered the maximum wind speed from 15 mph to 10 mph. This modification may appear minimal, but may prove to be substantial.

In an effort to quantify how much of an impact this would have had on the 2017 growing season, hourly average wind speed data (8 a.m. to 8 p.m.) from the Kansas Mesonet station at Parsons was utilized. These times were chosen because spraying these chemicals is allowed only between sunrise and sunset. In addition, spraying during temperature inversions is prohibited and research has shown that inversions are generally start one to two hours prior to sunset and diminish one to two hours after sunrise.

If we consider April 1 to August 31 as the main soybean growing season, using the 15 mph guideline, there were only 17 of the possible 153 days (11.1 %) that had any hourly reading above 15 mph. However, if the threshold were lowered to 10 mph, there were 54 days (35.3 %) where a reading about 10 mph was recorded.

One may argue that the window should be shortened to May 1 through July 31 since this is when spraying would more likely occur. Once again, only eight (8.7%) of the possible 92 days had a maximum wind speed above 15 mph. Using the 10 mph threshold, 34 days (37%) would reach wind speeds that would prevent spraying. Lowering the maximum by only five miles per hour had a three to four fold increase in days where spraying would be limited.

It must be pointed out that this only takes into account the wind speed. Of the remaining days in which spraying may be possible according to the wind speed, field conditions (moisture) may prevent spraying from even being possible. In addition, 2017 might have been a particularly windy growing season rather than the norm.

Our annual Agronomy Night Meeting in Independence will focus on dicamba and will be held on December 13th. Doug Shoup, Southeast Area Agronomist will present on how to use dicamba in a weed management plan and Roger McEowen, Washburn University Kansas Farm Bureau Professor of Agricultural Law and Taxation will discuss potential legal issues with the use and application of dicamba. To register for the meeting or if you have any questions, please call me at the office (620) 724-8233, or e-mail me at, or visit the Wildcat Extension District website at