By Mark Loux

We would like to first apologize for inadvertently providing what has proved to be false information all winter. We have been receiving conflicting and changing information on the legality of various Sharpen tank-mixes. 

One company in particular told us two weeks ago that they were absolutely certain that they would retain the supplemental labels for mixtures of their products with Sharpen into spring, and then last week we were told that they were retracting those labels. 

We were hopeful that there would be labels this spring to allow mixing of Sharpen with products that contain flumioxazin or sulfentrazone but this does not appear to be the case. The labels for these mixtures that existed last spring were apparently the result of some temporary regulatory glitch or wormhole or warp in the fabric of the universe. 

There are still some uncertainties in this situation – there is a supplemental label online for at least one sulfentrazone product that allows mixing with Sharpen but we suspect not for long.

We suggest contacting your local rep or dealer for the most up-to-date information on this as the spring progresses.

Here is the current situation per company involved, as far as we know: 

BASF – does not support and has never allowed mixtures of Sharpen with any other PPO herbicides per the Sharpen label.   BASF claims that there is a risk of crop injury from these mixtures, but has never shared data with us that support this.  One reason for their position is undoubtedly the desire to sell their own residual products – Optill and Scepter.  Unfortunately, their residual products do not provide consistently effective control of marestail. 

Valent/Dupont – retracted the labels for mixtures of Sharpen with Valor products and Envive in late 2012 and informed us that they would not have these labels for the spring of 2013. This also applies to Fierce, which received a label for soybeans about a week ago. 

FMC – retracted the supplemental labels two weeks ago that allowed the mixing of Authority products with Sharpen, and has informed us that these labels will not return for this spring. 

Dow – supplemental label that allows mixing Sonic with Sharpen can still be found online, and Dow informed us several weeks ago that this was an approved mixture per the Sonic label. We expect this could change since Sonic and Authority First are the same product. 

Syngenta - supplemental label that allows mixing Prefix with Sharpen can still be found online, and we were informed by at least one Syngenta person several weeks ago that this was an approved mixture per the Prefix label. 

So what is left to mix with Sharpen for residual marestail control if we cannot use flumioxazin or sulfentrazone products?  The most effective stategy based on our research would be to use metribuzin 75DF at 8 to 12 oz/A, or add some to premix products that already contain a low rate of metribuzin. 

Premix products that fit here – Canopy/Cloak DF, Matador, Boundary/Ledger. The lack of marestail control with the BASF residual products can also be fixed by the addition of an effective rate of metribuzin.  

What to do if you are locked into a flumioxazin or sulfentrazone residual product and end up too close to planting to use 2,4-D ester, or need a burndown more reliable on large marestail than glyphosate + 2,4-D? 

Options here include Liberty or a mixture of Gramoxone plus 2,4-D ester plus metribuzin. Liberty can be mixed with any residual herbicide and is generally effective for control of emerged marestail, but should also be applied with metribuzin if possible.

We suggest use of at least 32 oz/A of Liberty, and 36 oz/A if the marestail have much size. With the exception of early spring, we have not been successful at controlling marestail with Gramoxone treatments unless both metribuzin and 2,4-D are in the mix. Activity of Liberty and Gramoxone will be optimized by applying in a volume of 20 gpa. Avoid use of nozzles that produce large droplets.