Preharvest treatment options for dry edible beans
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
weeds not controlled by earlier weed management practices, and “green”
stems or leaves of dry bean plants can be a major problem for growers
who are trying to direct harvest. Preharvest herbicide treatments to
desiccate green tissue can help reduce harvesting issues. In Michigan,
there are four different herbicide options that can be used for
preharvest treatments in dry beans. These products are Gramoxone Inteon
2SL (paraquat), glyphosate (several formulations), Aim 1.9EW
(carfentrazone), and Valor 51WG (flumioxazin). Valor just recently
received a registration as a preharvest treatment in dry beans.
Depending on your cropping situation, one of these herbicides may be
more beneficial than the others based on their intended use and label
restrictions. Below are benefits and additional use precautions that
should be considered when choosing a preharvest treatment.
Gramoxone Inteon 2SL (paraquat) was one of the first products registered as a harvest aid in dry beans. The primary use of Gramoxone Inteon is to desiccate uncontrolled weeds that may interfere with harvest. However, Gramoxone Inteon will also help desiccate dry beans that may have some green leaves or stems. In MSU trials, Gramoxone Inteon has been the herbicide with the quickest speed of activity, showing greater control of weeds and desiccation of dry beans three days after treatment. However, by seven days after treatment dry bean desiccation with Valor and 14 days after treatment weed control and dry bean desiccation with glyphosate (Roundup) have been similar to Gramoxone Inteon. Gramoxone Inteon is a contact herbicide so desiccation is dependent on good spray coverage. The use rate of Gramoxone Inteon is 1.2 to 2.0 pt/A. In MSU trials we have generally applied two pt/A. A non-ionic surfactant (NIS) at 0.25 percent v/v must be applied with Gramoxone Inteon. The application timing for Gramoxone Inteon 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. Gramoxone Inteon can be applied as a split application if weed and dry bean growth is lush and vigorous, but the total application rate cannot exceed 2 pt/A. There is a seven-day preharvest restriction between application of Gramoxone Inteon and dry bean harvest. Gramoxone Inteon is also a restricted-use pesticide, so a private or commercial pesticide applicator’s license is required for use of this product. Glyphosate (several formulations) should only be used to control weeds that hinder harvest and not for dry bean vine desiccation. Glyphosate is the most effective herbicide for broad-spectrum weed desiccation followed closely by Gramoxone Inteon of the herbicides labeled for preharvest application. Glyphosate is a systemic herbicide so it generally takes 10 to 14 days after application for maximum activity. Glyphosate should only be applied when beans are in the hard dough stage (30 percent moisture or less). Earlier applications have resulted in glyphosate residues found in harvested beans. There is a seven-day preharvest restriction between glyphosate application and dry bean harvest and only one glyphosate application should be made per year. Glyphosate should not be applied to beans grown for seed or to plants where vines or hay may be used to feed livestock. There are several glyphosate formulations that are labeled for preharvest treatments in dry beans, it is important to examine the individual product labels to make sure a particular glyphosate formulation is labeled for this use. The maximum use rate of glyphosate is 0.75 lb ae/A, which is equivalent to 22 fl oz/A of Roundup WeatherMax and Roundup PowerMax or 24 fl oz/A of Durango DMA or 32 fl oz/A of a 3 lb ae/gal glyphosate formulation. Ammonium sulfate (AMS) at 17 lb/100 gal should always be added, regardless of glyphosate formulation.
Valor 51WG (flumioxazin) is the newest herbicide labeled as a preharvest treatment in dry beans. Valor has provided similar desiccation of dry beans as Gramoxone Inteon, by seven days after treatment in several MSU trials. However, weed control has not been quite as effective. There is not an initial application timing listed on the label, but I would recommend using similar guidelines as Gramoxone Inteon. These guidelines are when the dry bean crop is mature, when at least 80 percent of the pods are yellowing and mostly ripe, and no more than 40 percent (bush-type beans) or 30 percent (vine-type beans) of leaves are still green. Valor should be applied at 1.5 to 2.0 oz/A with 1 qt/A of a methylated seed oil (MSO) or crop oil concentrate (COC). In MSU trials, 1.5 oz/A of Valor with MSO has provided similar desiccation as two oz/A of Valor. Dry beans can be harvested within five days of application, but in MSU trials it generally takes seven to 14 days after treatment to reach maximum dry bean desiccation. Depending on your crop rotation, the residual activity of Valor activity can be a drawback or benefit. If your intended rotation is corn or soybean Valor can provide some residual control of winter annual weeds prior to planting these crops. However, if you are planning on planting winter wheat after a desiccation application of Valor, there needs to be one month and one-inch of rain before planting this crop. For sugar beets the rotation restriction was just changed to four months if the soil is tilled and eight months if the soil is not tilled with a maximum application rate of two oz/A of Valor. However, we have not examined these new rotation restrictions in Michigan and I would recommend not using Valor as a desiccation treatment if you are intending to plant sugar beets the following spring. Another thing to keep in mind is Valor residues can many times be trapped in poly-tanks and hoses in sprayers if not adequately cleaned. There are special sprayer cleanup procedures listed on the label. It is important to follow these procedures, so there is not a problem with tank-contamination in the following spray loads.
Aim 1.9EW (carfentrazone) has consistently been the least effective preharvest herbicide for weed and dry bean desiccation in MSU trials. However, if this is the herbicide that you choose to use, there are a few guidelines that need to be followed. The application timing is similar to Gramoxone Inteon. These guidelines are to apply Aim when the dry bean crop is mature, when at least 80 percent of the pods are yellowing and mostly ripe, and no more than 40 percent (bush-type beans) or 30 percent (vine-type beans) of leaves are still green. The Aim use rate is one to two fl oz/A and Aim should be applied with one percent v/v MSO. The preharvest interval for Aim is three days.