Volume
2 Issue
6
June 28,
2005
Drift Injury on Soybean and
Interactions with Scheduled Postemergence Herbicides
As fields of small grain, sugarbeet, and corn recover
from wet conditions, you will quickly see spray rigs
actively treating fields with herbicides. Too frequently,
as you are driving in the region you can smell herbicides
from your vehicle before you see the sprayer, as
applications are being made in wind conditions that are
less than ideal. Unfortunately, soybean is very
susceptible to drift from plant growth regulator (PGR)
herbicides used in many tank mixes.
 Drift
injury on soybean is frequently from PGR herbicides such
as Stinger, Curtail, 2,4-D, Clarity and a host of products
that contain these same active ingredients. Symptoms from
PGR injury include leaf cupping, strapping, and puckering
(Figure 1). Depending on the severity of injury the plants
may also be stunted, delayed in maturity, brittle, and
appear to have a profusion of leaves from the upper part
of the plant as the internodes have been shortened.
 A
recent article in Weed Science by Kelly et. al.
(2005) discusses the influence of selected PGR
herbicides on soybean at various stages development. They
applied the herbicides at reduced rates to simulate
amounts common/possible in drift situations. The herbicide
rates ranged from 0.1 to 3.2 % of the high labeled rates
of Clarity, Distinct and Stinger used in corn and from 10
to 32 % of the high labeled rate of 2,4-D. This study
found that soybean is the most sensitive to Clarity
followed by Stinger and Distinct and is least sensitive to
2,4-D. Others have reported that injury occurring at
reproductive stages have a higher probability of reduced
yields, however, this study shows the potential for yield
loss is just as high at V3 developmental stage as at the
R2 stage (Table 1).
 To
us, the more interesting part of this research looked at
the interaction between a drift rate of Clarity applied
with normal rates of herbicides used on soybean (Table
2). Kelly et. al. found that soybean injury was more
severe when Clarity plus the soybean herbicide was applied
than the level of injury you would expect by adding the
injuries from Clarity and the other herbicide applied by
themselves (synergy). This synergistic increase in injury
was evident even six weeks after application with
treatments containing Pursuit, Raptor and Flexstar. The
increase in injury also resulted in reduced yields with
Pursuit and Raptor one of two years and was observed both
years with Flexstar (data not shown). There was not a
synergistic effect with Clarity and glyphosate to reduce
yield (although they did observe some increased visual
injury at the V7 stage of development in 2003).
This research indirectly addresses an important
management issue that occurs when producers have
experienced early season drift injury from a PGR herbicide
but have not made their postemergence weed control
applications. What should he do? Delay his postemergence
application to allow the soybean plants to recover from
the drift injury (result: larger weeds) or make the
herbicide application while weeds are still small. This
research suggests that with a Roundup Ready variety there
is not much additional risk by making a glyphosate
application whenever you can get in the field. But, with
conventional herbicides (especially Flexstar) you risk
additional yield loss by not allowing the plants to begin
to recover.
It is difficult to predict the yield response to damage
from PGR herbicides on soybean because environmental
conditions and a many other factors influence the plants
ability to recover from the injury. However, this research
suggests that we need to be careful when managing soybeans
with PGR herbicide injury so we don’t increase injury to
the soybean plants and possibly increase yield loss.
Literature Cited:
Kelley, K.B., L.M. Wax, A.G. Hager, and D. E. Riechers.
2005 Soybean response to plant growth regulator herbicides
is affected by other postemergence herbicides Weed Sci:
53:101–112.
Carlyle Holen U of M IPM Specialist
and
Doug Holen, Regional Extension Educator
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