I assume you are evaluating data and reviewing information that will guide your decision regarding the re-registration of dicamba for use in dicamba-resistant (DR) crops. As you know, farmers have a critical need for additional tools to help manage herbicide-resistant weeds. However, dicamba must be able to be used in DR crops while posing minimal risks to non-DR soybean and other sensitive plants in the agricultural landscape. The past four years have clearly shown the limitations of the current dicamba system in protecting sensitive plants in areas where DR crops are grown.
I believe a multi-pronged approach including the following steps is needed to reduce off-target dicamba movement and injury to sensitive plants.
1) Fast track approval of new formulations IF they significanlty reduce volatilization under field conditions compared to existing formulations;
2) Rapid phase out of the older, higher-volatile dicamba formulations used in row crops; and
3) Work with state regulatory agencies to develop a better system of penalizing ‘habitual offenders’ who violate pesticide labels and disregard safe pesticide use.
Placing new restrictions on existing products and requiring additional training for applicators is NOT the answer.
The phase out of older dicamba formulations is likely the most controversial of my recommendations. Some will say this creates ‘dicamba monopolies’ and increases the cost of weed control in other cropping systems. However, in 2020 it was clear that movement of dicamba from Iowa corn fields was a significant contributor to off-target injury. I have no idea how frequently the older formulations are illegally sprayed on DR crops, but this is frequently used as an explanation/excuse for off-target injury. Dicamba products with use patterns that have lower risks of off-target movement would not necessarily need to be affected by this action (e.g. Trimec).
I can think of several examples where EPA stopped the sale or restricted the use of herbicides when ‘safer versions’ were developed (e.g. replacing alachlor with acetochlor; reducing labeled rates of non-resolved metolachlor formulations when the more-active resolved isomer was introduced). We know that volatilization of dicamba contributes to off-target movement, why allow sales of the higher-volatility formulations when improved versions have been developed?
The unique properties of dicamba make it impossible to guarantee a risk-free product in terms of off-target injury. However, by looking beyond the label of the products currently used in DR crops I believe the risks associated with this system can be reduced to an acceptable level, thus allowing farmers the continued use of this weed management tool.