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Pre-seed burn-off herbicides

Make sure you’re following good chemical rotations. Know your 
active ingredients before you plan your pre-seed burn-offs

Time and again farmers are warned about the dangers of the development of herbicide resistance. They are told over and over not to use the same product repeatedly and to rotate chemical groups. Yet glyphosate, arguably modern agriculture’s most important herbicide, is still used every year on many farms, and by some farmers multiple times per year for burn-off, in Roundup Ready crops, for pre-harvest and post-harvest weed control.

World-wide, there are 24 weed species that have developed resistance to glyphosate. In Canada there are documented cases ofthree glyphosate resistant weeds: giant ragweed, horsetail, and in 2012 glyphosate resistant kochia was confirmed in Alberta. The discovery of Group 9 resistant kochia is even more troubling because in some cases the plants were also resistant to Group 2 chemistry, severely limiting the control options that are left for this tough to control weed species.

To prevent further herbicide resistance development there are best practices which every farmer should follow when applying herbicides. This includes herbicide use for pre-seed burn-off. The DuPont Canada Crop Protection website (go to, then type “pre-seed burn-off” into the search box) outlines these pre-seed burn-off best practices.

Glyphosate burn-off products

There is one more practice that farmers need to add to DuPont’s best practices list: know your herbicides.

This is especially important for glyphosate given the many brand names glyphosate is sold under. Not all glyphosate brands are the same in terms of formulation, registered usages, tank mixes or strength but all are equally susceptible to the development of resistance. Once glyphosate resistance develops, it will extend to all glyphosate brands. Simply rotating brands of glyphosate will not prevent resistance development.

As of December 2012, the Alberta Agriculture herbicide selector website listed 22 registered brands of glyphosate that farmers could use for pre-seed burn-offs. There will likely be more names added by spring. All of these herbicide brands have only glyphosate as the active ingredient.

Glyphoste tank mixtures

Instead of relying on glyphosate alone for a burn-off, there are a number of pre-packaged products which combine glyphosate with second product that has a different mode of action.

These products offer the broad spectrum control of glyphosate plus another active ingredient to control weeds which glyphosate may be weaker on like buckwheat or dandelion or to control roundup ready volunteers. Having two active ingredients also reduces the chances of development of herbicide resistance.

However, farmers need to know the second active ingredient in these prepacks. In many cases it may be the same active you will be using in-crop. This can increase resistance issues for the second active.

An alternative to using a prepackaged mix of glyphosate and a second active is to tank mix an existing herbicide with glyphosate on farm. There are 11 registered glyphosate tank mix options for pre-seed burn-off at time of writing.

Monsanto, the original manufacturer of glyphosate, is in fact recommending tank mixing Roundup Transorb HC with Heat to optimize weed control in pre-seed burn-offs. In a December 10, 2012 news release, Sean Dilk, weed management technical lead, Monsanto Canada states: “Mixing heat with Roundup Transorb HC is an important part of sustainable weed management for reduced tillage operations.”

Joel D. Johnson, BASF’s brand manager, Western herbicides, adds: “By using multiple modes of action, you can delay herbicide resistance. Mixing HEAT with Roundup Transorb HC provides a second mode of action for pre-seed burn-off and chemfallow treatments. Not only do you get the fastest and sharpest burndown, it’s effective in managing volunteer canola (all biotypes) and kochia as well as many other tough perennial and annual weeds.”

To promote the use of the Roundup Transorb HC and Heat tank-mix, Monsanto and BASF are offering a $0.50 per acre discount on Roundup Transorb HC when farmers purchase matching acres of Heat and Merge. The discount will be available at participating retailers on products sold between Nov 15, 2012 and June 30, 2013.

Non-glyphosate burn-off

Unfortunately there are very few alternatives to the low cost, pre-seed in multi-crops, broad spectrum weed control glyphosate offers. However, there other products registered for use in specific crops that farmers can consider using. When compared to glyphosate, each of these have disadvantages which must be factored in to your herbicide selection decision.

However, these products enable farmers to occasionally rotate away from glyphosate. †

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