The Pros and Cons of Dry Bean Desicants
June 21, 2007
A dry bean desiccant can help evenly dry down the crop and weeds to hasten harvest. For some growers, desiccation permits direct harvesting, allowing them to skip the steps of knifing and windrowing.
However, keep in mind that a desiccant doesnt speed up crop maturity; it just shortens the time between maturity and harvest. Thus, the crop must be physiologically mature (ready to swath) before a desiccant is applied.
There are three products currently labeled for pre-harvest application in the Northarvest region, and all three have their drawbacks.
The drawback with Roundup (glyphosate) is that its labeled for late season weed control in edible beans, and is not labeled for use as a crop desiccant. NDSU notes to apply glyphosate after dry bean pods have turned yellow and leather in texture; at hard dough bean seed stage and 30% or less seed moisture. Allow a 7 day pre-harvest interval, and do not apply to dry beans grown for seed, because reduced germination/vigor may occur.
The drawback with paraquat (Gramoxone Max, Gramoxone Inteon) is that its a restricted use pesticide. Aim (carfentrazone, + MSO adjuvant) is not a restricted use pesticide, but the drawback with Aim is that it does poorly with vine desiccation (see tables, from NDSU data).
NDSU extension weed specialist Richard Zollinger notes that research trials with Aim in 2005 indicated that the product at 1 oz/ac usually gave similar desiccation as paraquat at 1 pt/ac, but Aim at 2 oz/ac + MSO gave around 5% greater desiccation than paraquat.
Other observations from the trials in 2005:
Aim applied with MSO at 1 qt/ac usually increased desiccation as compared to adding petroleum oil (COC) at 1 qt/ac.
Aim at 2 oz/ac gave about 10% greater desiccation than 1 oz/A at 5, 7, and 14 days after application (DAA) (61/73, 63/74, and 71/75).
All experimental treatments with Aim did not dry vines down much better than the untreated check.
NDSU advises applying both paraquat and Aim when at least 80% of pods are yellow/brown. Apply when no more than 40% (bush type beans) or 30% (vine type) of the leaves are still green. Sequential applications may be needed, and thorough coverage is essential. Allow a seven day pre-harvest interval for paraquat and three days for Aim.
Zollinger notes that the desiccants can be expected to perform more effectively in warm, sunny conditions compared to cloudy, cool conditions.
Consult with an agronomist well before harvest about the pros and cons of using a desiccant.