Alabama Soybeans: Varietal Response to Saflufenacil (Sharpen)

Photo: Alabama Cooperative Extension

What is saflufenacil?

Saflufenacil is a group 14 PPO herbicide. Saflufenacil is the active ingredient in Sharpen herbicide and one of the active ingredients in Verdict herbicide. This chemistry provides excellent burndown control of marestail/horseweed and other broadleaf weeds in soybeans when used properly.

Good coverage (minimum of 15 GPA water volume) and a methylated seed oil (MSO) are required for optimal performance. Soybeans can be planted immediately following an application of 1.0 oz/Acre of Sharpen or 5.0 oz/Acre of Verdict respectively, on non-coarse soils (see herbicide labels for other restrictions on rate and soil type).

Silt loam or silty clay loam soils commonly found in the TN Valley Region of Alabama fall into this category and can be planted with no preplant interval at the above rates.

When is Soybean Varietal Sensitivity Seen Following an Application of Saflufenacil?

It has been documented that soybean varieties differ with respect to level of tolerance or sensitivity to saflufencacil. A varietal response is typically seen when an application of Sharpen or Verdict is made and a sensitive variety of soybean is planted immediately following the application, and rainfall is incurred while the germinating seeds are imbibing water or cracking the soil surface.

During these events, the herbicide is imbibed into the seed or comes in contact with the hypocotyl when it is emerging. Poor closure of the seed furrow, especially on conventionally tilled soils and a heavy rain event following application and planting can also contribute to injury.

2017 Screening Results

Knowing that varietal sensitivity does exist, we have found that an in-field screening of commonly planted soybean varieties for this area is a valuable tool. This year we screened 37 soybean varieties. Please note that these results are based on silt loam soils. These plots were sprayed one day after planting with 1.5 oz and 3.0 oz/Acre of Sharpen respectively, on June 3, 2017.

The 1.5 oz/Acre rate is off label for a zero day preplant interval and the 3.0 oz/Acre rate is off label altogether. These rates were only used for research purposes to create a worst case scenario and are not encouraged. The 1.5oz rate was used to rate varietal sensitivity while the 3oz rate was used to confirm varietal tolerance.

Knowledge of sensitivity is important but knowing what varieties are fully tolerant is especially important and that is also why these use rates were chosen. Rainfall of 0.75″ was incurred one day after application followed by 0.25″ the next day. An additional 1.0″ of irrigation was applied at cracking for a total of 2.0″ rainfall and irrigation combined.

These plots were replicated and untreated running checks were present throughout the trial. Ratings were taken at 10 and 20 days after application. Ratings were based on degree of stunting and visual leaf injury. Please note that these are the visual results we observed at this location under these conditions.

More or less injury could be observed under different conditions. Environmental conditions can have a tremendous impact on the level of observed sensitivity. Several entries were rated as more sensitive this year than in previous years under these conditions. Consider multiple factors and sources of information when choosing a soybean variety.

For detailed listing of soybean varieties and sesitivity rating, please refer to this document.



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