There is a new herbicide named Sharpen available for burndown in soybeans this spring. It is a nice change to be able to talk about a new herbicide — they have been few and far between over the past decade.

Although Sharpen is a new herbicide it is not a new mode of action. Sharpen is in the PPO herbicide family, which contains among others, Valor.

Sharpen differs from Valor in two significant ways.

The first is that it will translocate more effectively through leaf material than Valor and as a result can provide post control of weeds like horseweed.

The second difference is that Sharpen at the typical use rate of 1 ounce per acre will provide only about seven to 10 days of residual control of small seeded broadleaves. In comparison, Valor typically provides four to five weeks of residual control.

We looked at Sharpen as a potential new burndown option in soybeans and cotton over the past six years. I was and continue to be very impressed on how well it controlled glyphosate-resistant horseweed (marestail).

We saw it very consistently control horseweed at the 1 ounce per acre rate tank-mixed with glyphosate or alone with MSO surfactant.

The standard horseweed burndown most Tennessee farmers have used is 8 ounces per acre of dicamba tank-mixed with glyphosate. The tank mixture of 1 ounce of Sharpen tank-mixed with glyphosate controlled glyphosate-resistant horseweed similarly to the standard dicamba/glyphosate tank mixture.

The big advantage Sharpen has over dicamba as a burndown option for horseweed is that soybeans can be planted at any time behind a Sharpen application. Every spring I get calls from farmers who have yet to burndown horseweed in a field but still want to plant the field that day. We now have an effective option for that problem.

Sharpen as a burndown application will be very effective controlling horseweed, giant ragweed and Palmer amaranth if it is less than 4 inches tall. As we know, all of these can be glyphosate-resistant, and so a new tool for their control is welcome.

Sharpen will not control some of our more common winter annual weeds like poa and ryegrass. It is also weak on henbit and primrose. That is why I like it tank-mixed with glyphosate or Gramoxone Inteon.

Sharpen is also labeled as a preplant application in cotton as well. In my opinion, it will not have the utility in cotton that it has in soybeans because it is labeled with a 42-day waiting period between a Sharpen application and cotton planting. With that label restriction, I feel that a dicamba-based burndown applied 30 to 15 days before planting (DBP) is still the best fit in cotton.

Valor or Reflex can then be tank-mixed with that early dicamba-based burndown to provide residual control of horseweed and help out some on the front end of the Palmer amaranth emergence window.

The other option is to forgo the residual option with the early burndown and plan to use Gramoxone Inteon plus Cotoran or Caparol to eliminate any newly emerged horseweed as well as provide a couple weeks of control of Palmer amaranth.

A number of folks have asked if Sharpen will fit in their soybean burndown programs. The answer in many cases is yes. However, talking to many retailers, it sounds like supply will not meet the Mid-South demand for Sharpen.

e-mail: lsteckel@utk.edu