Alabama Soybeans: How Sensitive Is Your Variety to Sharpen and Verdict?

Photo: Alabama Cooperative Extension

Many if not most fields where full season soybeans will be planted have already had a burndown herbicide applied. Wheat harvest is just around the corner and double cropped soybean planting will soon follow. Sharpen and Verdict, two products that contain saflufenacil, are commonly applied in combination with glyphosate as a burndown for these fields that contain heavy marestail pressure.

Either of these products provide excellent control of marestail but some varieties of soybean are sensitive to these herbicides. Sensitivity is typically only seen when an application is made right behind the planter and a large rainfall event is incurred soon after.

Please note that in a study from 2014, we only observed yield loss from sensitive varieties (2.4 bushels/Acre) when off label rates were used at planting. We have conducted an in-field screening the past two seasons to determine which varieties exhibit sensitivity.

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.

Table1: rating scale utilized
Safe     Tolerant
Caution     Moderately Tolerant
Warning     Sensitive
Danger     Highly Sensitive

Table 2: Soybean varietal response to saflufenacil
ASGROW     46X6     Warning
ASGROW     46X7     Danger
ASGROW     47X6     Warning
ASGROW     49X6     Warning
ASGROW     53X6     Warning
ASGROW     55X7     Warning
ASGROW     59X7     Warning
PROGENY     4516RXS     Danger
PROGENY     4620RXS     Danger
PROGENY     4799RXS     Danger
PROGENY     4757RY     Warning
PROGENY     5016RXS     Warning
PROGENY     5376RX     Safe
PROGENY     5417RX     Warning
PROGENY     5752RY     Warning
PIONEER     45A23X     Caution
PIONEER     46A93X     Safe
PIONEER     46T30X     Warning
PIONEER     48A60X     Danger
PIONEER     48T27X     Caution
PIONEER     52A26R     Safe
PIONEER     54A54X     Safe
PIONEER     55A49X     Safe
CROPLAN     RX4516S     Danger
CROPLAN     RX4687S     Caution
CROPLAN     R2C4775     Warning
CROPLAN     RX4817S     Caution
CROPLAN     RX4825     Danger
CROPLAN     RX5136     Danger
CROPLAN     RX5427     Danger
CROPLAN     R2C5656     Danger
CREDENZ     4540LL     Caution
CREDENZ     4818LL     Safe
CREDENZ     4820LL     Warning
CREDENZ     4748LL     Warning
HORNBECK     LL4950     Warning
HORNBECK     LL4953     Danger

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