Agroup of seven extension staff from Ohio’s Purdue University have issued a publication on the pros and cons of 2,4-D- and dicamba-tolerant crops.
Two companies are set to introduce these products in combination with glyphosate as a means of controlling weeds that have become resistant to glyphosate alone. Opponents say that widespread use of these older and drift-prone broadleaf products will put neighbouring crops, especially vegetables, at risk.
Dow AgroSciences has developed its Enlist seed system for corn, soy and cotton, along with Enlist Duo herbicide that contains glyphosate and choline, a new formulation of 2,4-D which is said provides ultra-low volatility, minimized potential for drift, lower odour, and better handling characteristics than other 2,4-D amine or ester formulations. The Dow system is also resistant to glufosinate.
Monsanto is developing the Roundup Ready Plus Extend system combining glyphosate and dicamba. Monsanto is collaborating with BASF to address dicamba’s potential to injure off-target vegetation through drift or volatilization. They plan to make stewardship conditions part of the product label, including using spraying technologies that produce very coarse to ultra-coarse droplets, spraying only when wind speeds are less than 10 m.p.h. or when conditions are favourable for temperature inversions, and requiring buffer zones.
The researchers note that concerns about drift from 2,4-D and dicamba are not new.
“Both herbicides have been used post-emergence for more than 40 years (dicamba) and 60 years (2,4-D) in many different crops and are still widely used today.”
However, they say that adoption of these systems would mean the acreage sprayed with 2,4-D and dicamba would increase to encompass the majority of agronomic acres in the United States.
“Since much of this acreage could be sprayed two or three times each growing season, some argue that it greatly increases the potential for off-site movement — even if most applications occur under the best of conditions — and for weeds to develop resistance to 2,4-D or dicamba.”
The researchers say drift concerns are being addressed by both companies through the development of newer, lower-volatility formulations.
“However, a concern is that low-cost, generic formulations of both 2,4-D and dicamba are still readily available and growers may turn to these options if economics favour a lower application cost.”
In their summary, the researchers say the new technologies “can help maintain near-term productivity in our efficient, simplified monoculture systems of commodity crops.
“However, we must not become overly reliant on this technology as the only solution to manage weeds and maintain high crop productivity. A diversified approach to weed management must not be lost. The most durable and productive weed management system must integrate many tools, including genetic, cultural, non-chemical, and chemical methods.”
The full report is available at https://mdc.itap.purdue.edu. Search for ID-453-W.