What is the progress in the development of tolerant GMO plants with double resistance (for example: plants with two genes, one that confers resistance to glyphosate and a second one for conferring resistance to any other pesticide?

I have thought about it. I guess it could be implemented to avoid overuse of glyphosate year by year, by reducing the chances of resistant weeds.

Expert response from Brian Scott

Farmer

Wednesday, 03/12/2014 17:09

This is an excellent and timely question.  The U.S. Department of Agriculture has just recently deregulated Dow AgroSciences’ Enlist traits for corn and soybeans.  The Enlist system consists of crops with herbicide tolerance for both glyphosate and 2,4-D. Cotton will also get this treatment.  Enlist Duo herbicide will accompany the crops as a premixed formulation of the two herbicides with a reformulated 2,4-D Dow calls 2,4-D Choline with Colex-D technology.  This formulation greatly reduces the signature odor of conventional 2,4-D and risk of off target movement.  In the future the Enlist program will also add glufosinate tolerance to the program bringing crops to market with tolerance to three herbicides.  Monsanto's Xtend program will be coming soon as well, bringing glyphosate and dicamaba tolerance.  In the very near future farmers will have many more tools in their weed management toolbox.

Reducing weed resistance is a key part of using more than one herbicide.  There are many modes of action herbicides use to kill weeds.  This is a great reason to use the products I listed above.  When applying more than one mode of action to a weed (or disease or pest) the odds of resistance to both modes occurring within a given plant are extremely low.  That being said, we still need to rotate modes of action, crops, and other weed management practices.  

If a farmer has an issue with glyphosate resistant marestail and looks to the Enlist program to control that weed it will work.  2,4-D does a great job of controlling marestail.  This weed shows up in soybeans fields in the Midwest, and late emerging weeds are difficult to control if they are resistant to glyphosate.  And because they are already resistant to glyphosate's mode of action, when the farmer applies something like Enlist he is really only treating that weed with the 2,4-D component since the glyphosate portion will be ineffective.  So farmers can't rely solely on just one of these new herbicide tolerance traits to combat resistant weeds.  Rotating modes of action will still remain an important part of weed management. 

Tank mixing different herbicides is not a new idea. For post-harvest or pre-plant applications called “burndown,” a mix of glyphosate and 2,4-D is a common mix.  Glyphosate will do a good job killing grasses and 2,4-D will eliminate broadleaves such as dandelions.  Of course glyphosate alone will take out just about everything, but 2,4-D has another advantage.  Glyphosate is a contact killer meaning it will only kill the weeds it touches when sprayed.  2,4-D has some residual activity allowing it to kill weeds that have yet to emerge.  It is also not unusual to mix fertilizer, insecticide or fungicide with a herbicide to reduce application costs and trips across a field with expensive equipment provided the timing is right for each product.  Multiple herbicide resistant crops are just moving the window for tank mixes further into the growing season for more effective weed control.  The next new technology in weed management is going to be biologicals.

Hopefully I've answered your question thoroughly.  If you have any more items to discuss please leave a comment.