Our Family Farms

Dicamba is a weed killer and perhaps the most widely used chemical (along with 2,4-D) that represents the so-called pesticide treadmill. The pesticide treadmill comes in to play because the most commonly used weed killer on GMO crops, glyphosate, has been used too much for too long and there have emerged glyphosate resistant weeds on well over 65 million prime farmland acres in the U.S. alone, an area the size of the entire state of Oregon. For many years the need for another weed killer specifically for use with GMO crops was obvious but farmers did not have dicamba tolerant crops until 2013-15 (corn, then soy then cotton ). Dicamba works like 2,4-D by killing plants through growth stimulation beyond available nutrients.  The growing edge of the plant dies from lack of nutrients.

Why has dicamba become so controversial?  The manufacturers know well that this weed killer is highly volatile, even capable of evaporating off the sprayed crops  and becoming easily spread to other crops.  But industry promised a new chemical formula of dicamba to be used with the new GMO crops, a chemical formula that would not be so volatile and thus would stay put on the sprayed fields when released under “calm” wind conditions. 

But the results of volatility and spray drift issues are severe as documented by this farmer who grows soybeans on 6,000 acres. "We've had damage across just about every acre of soybeans we farm in southeast Missouri," said Hunter Raffety, a farmer in Wyatt, Mo. "In our small town, even the ornamentals and vegetables in backyards, have been lost. It's a big problem."

There are at least two complex issues.  First, the GMO seeds expressing tolerance to dicamba became available before the new generation of the chemically modified dicamba.  EPA only approved the new supposedly less volatile dicamba in November 2016, two years after the availability of the new GMO tolerant soy seeds became available to farmers. The old dicamba is especially known to be volatile and can spread even after the droplets become deposited on target plants. The second issue is that the lower cost for old formulations of dicamba are still readily available for grower purchase.

Reasons given for drift and volatility issues with dicamba are many and seem to vary among the states of the mid-south vs. the north. For Example, Arkansas, Missouri, and Tennessee have had more off-target cross farm contamination issues than further north in the corn belt. But many complaints have also been filed by farmers in Illinois, Alabama, Minnesota, Texas, and North Carolina. Three states (Arkansas, Missouri, and Tennessee) have filed partial bans and other restrictions on dicamba use for the remainder of the current crop year.

The majority of dicamba applications onto GMO dicamba-tolerant soybeans are currently made as the crop approaches reproductive stages.  In the past, prior to GMO tolerant crops, dicamba was used largely as a pre-emergent product and applied very early in the growing season. Now susceptible crop varieties including orchards and non-GMO soybeans, etc are at greater risk because dicamba applications are made later in the crop year. Due to later application dates, temperatures are likely to be higher. The higher the temperature, the greater the likelihood of vapor drift.

One may wonder why there is a cross contamination problem now with the increasing use of dicamba and but not so much with the more commonly used glyphosate-based herbicides.  Historically most farmers remember that corn is highly sensitive to low exposures to glyphosate.  But by comparison soybeans are 200-fold more sensitive to dicamba than corn is to glyphosate (see image).