We the undersigned want to make clear that if Monsanto and Dow's new corn makes it past the USDA and into farm fields, it will mark the beginning of at least another decade of ramped-up chemical-intensive farming of a few chosen crops (corn, soy, cotton), beholden to a handful of large agrichemical firms working in cahoots to sell ever-larger quantities of poisons, environment be damned. If it and other new herbicide-tolerant crops can somehow be stopped, farming in the US heartland can be pushed toward a model based on biodiversity over monocropping, farmer skill in place of brute chemicals, and healthy foodWe the undersigned want to make clear thatinstead of industrial commodities.
Even by Down and Monsanto's reckoning, a new stacked 2,4-D/Roundup-ready product would immediately lead to an increase in herbicide use, because the companies have been advocating an herbicide program that combines current rates of Roundup use with a roughly equal amount of 2,4-D.  That's good for sales, but not so good for the environment.
And wouldn't such an herbicide cocktail just lead to weeds that defy both? All in all, chances are actually quite high that this collaborative product from Monsanto and Dow Chemical will unleash a new generation of superweeds that resist both Roundup and 2,4-D.  If 2,4-D resistance does indeed emerge, farmers will likely respond just as they responded to the advent of Roundup resistance--by applying ever higher doses.  
The main ecological concern with an explosion in 2,4-D use is pesticide drift.  The compound is said to be highly volatile and prone to be carried on the air, where it can do damage to non-target plants like the neighbor's vegetable farm.  If you are a farmer who is determined not to use a stacked 2,4-D/Roundup seed, you could be forced to if your neighbor's 2,4-D spray keeps knocking down your corn.
The advocacy group Beyond Pesticides points to both epidemiological and lab-based evidence linking it to non-Hodgkin's lymphoma and other cancers.  It is also an endocrine disruptor, meaning it can interfere with the body's hormone messaging system and can alter many essential processes.
And finally, there is simply no reason to send a flood of this carcinogen onto U.S. farm fields, where it will likely run off into ground water, as both Roundup and Syngenta's toxic herbicide atrazine already have.
On behalf of everyone concerned for the future of American farmland, clean water, and small farms everywhere, we urge you not to approve 2,4-D.  Thank you for taking the time to read our letter and consider our plea.