Sharpen as a dry bean harvest aid
Sharpen is an effective harvest aid in dry beans, but has the potential to cause problems when dry beans follow dry beans.
Sharpen 2.85L (saflufenacil) is a herbicide labeled for use as a harvest aid in dry edible beans and has been an effective dry bean desiccant in Michigan State University trials and grower fields. Sharpen has similar speed of activity as Gramoxone and is quicker than glyphosate and Valor. Sharpen is a contact herbicide, so desiccation is dependent on good spray coverage. Sharpen can be applied at rates up to 2 fluid ounces per acre. However, in MSU trials, 1 fluid ounce per acre of Sharpen with MSO (1 percent v/v) + AMS has provided similar desiccation as 2 fluid ounces per acre, so we recommend the 1 fluid ounce per acre rate.
The application timing for Sharpen is when the dry bean crop is mature, at least 80 percent of the pods should be yellowing and mostly ripe and no more than 40 percent (bush-type beans) or 30 percent (vine-type beans) of leaves still green. There is a two-day pre-harvest restriction between applying Sharpen and dry bean harvest, however it generally takes seven days to reach maximum desiccation activity.
Crop rotation should also be considered when using Sharpen as a pre-harvest herbicide. Winter wheat can be planted immediately after dry bean harvest. However, if rotating to sugar beets, take special precautions. The rotation restrictions for sugar beets are four months for a 1 fluid ounce per acre application rate of Sharpen and five months for a 2 fluid ounce per acre rate, this excludes months where the ground is frozen.
I was recently called out to a black bean field where the grower described his beans as “dying in waves” (see photo). In conversing with the grower, I learned he had planted navy beans there the previous year. The grower had applied 2 ounces of Sharpen Oct. 14 on his 2017 navy beans, and had planted his 2018 black beans June 7. The rotation restriction for dry beans following dry beans is six months, again excluding months where the ground is frozen.
The weeds on the borders of the field were unaffected, so drift was eliminated as a cause of the damage. I reviewed the soil temperature data from the nearest MSU Enviroweather station, which is about 7 miles away from the field. The ground froze on Dec. 9 and remained frozen through Feb. 20. The ground was unfrozen for 161 days, or 5.3 months, between application and dry bean planting.
In talking with MSU Extension weed specialist Christy Sprague, her best guess is Sharpen carryover caused the beans to die. If you intend to plant a sensitive crop (sugar beets, dry beans) after a Sharpen application, be mindful of the number of days the ground has been unfrozen between application and planting of the sensitive crop, particularly if the full 2 ounce rate is used.