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.
“Green”
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.