2004 Season Review: Weed Science
Tom Bauman, Professor, Botany & Plant
Pathology
Bill Johnson, Assistant Professor, Botany & Plant Pathology
Glenn Nice, Weed Diagnostician, Botany & Plant Pathology, Purdue University
We received a number of corn and soybean
herbicide injury reports during 2004. In some cases, the cause of the injury was
related to stressful weather conditions which reduced the plant’s
ability to metabolize or degrade the herbicide.
Herbicide Injury Issues
Growth Regulator:
Several cases of soybean growth regulator injury were
sent into the P&PDL in 2004. This is a common situation
in Indiana and the surrounding states or for that matter anywhere
where corn and soybean are grown in close proximity. Soybean
leaf puckering, cupping, and strapping are a common symptom when
exposed to low doses of a growth regulator such as 2,4-D, Banvel,
Clarity, Crossbow, Distinct, etc. In many cases if the
injury occurs early in the season there is not a yield response. However,
if the growing season leads to delayed corn applications and
injury occurs later in the soybean development yield effects
may be seen. For more information on growth regulator injury
on soybean, see the following publication (http://ipcm.wisc.edu/pubs/pdf/dicamba2004.pdf).
Lightning + Distinct:
Early August samples of corn were sent to the P&PDL. The
corn in the samples were severely damaged and malformed (Figures
1 and 2).
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 |
Figures
1 and 2. Malformed
corn leaves. |
This was also seen once in 2003. In all the cases, from
the information given, the only thing that was the same between
the samples were that Lighting + Distinct were tank mixed POST. Whether
this was the result of this tank mix was not determined. A
Lightning + Distinct tank mix is a labeled tank mix and has been
used by several producers at no detriment to the corn crop. However,
use of adjuvants, such as crop oil concentrate or methylated
seed oil is not recommended due to crop injury. Also weather
conditions can have an effect on ALS herbicides such as Lightning. If
this injury is herbicide related several things could be interacting
to induce this level of injury including environmental conditions
at time of application, the use of an adjuvant, and excessive
rates.
Weed Issues
Water-Cress:
In 2004, several samples of yellow water cress (Roippa
spp.) were received for identification. As to the
exact species of the samples it was not determined. Contradictions
in the literature concerning this group of plants made for an
indecisive identification. There were all found in areas
that were wet in the spring, but had dried out. For the
most part, water cress like a moist habitat and I believe that
in 2004 the increased concern about this plant is due to flooding
that Indiana experienced early in the season, allowing water
cress to become established in producers’ fields.
Giant Hogweed:
A new invasive plant by the name of giant hogweed (Heracleum
mantegazzianum) was identified in Indiana but an employee
of JFNew (a Natural Resource Consulting agency, www.jfnew.com). Giant
hogweed is a problem invasive in Australia, Europe, and Canada. In
the US it has been found in Maine, Michigan, New York, Pennsylvania,
and Washington. It is a large plant in stature resembling
a large cow parsnip (Heracleum maximum). For more
information about giant hogweed see the following
article “The
Infamous Giant Hogweed” (http://www.btny.purdue.edu/weedscience/2004/articles/gianthogweed04.pdf)
Greenbrier:
Several homeowners that have woods on their property
have sent in vines with or without spines that belong to the
Smilax genus. Plants from this genus are fairly common
in Indiana’s wooded areas and have been also known as “Jacob’s
Ladder”, “Bristly Sarsaparilla”.
Horseweed/marestail:
Horseweed (aka marestail) is weed common to Indiana
and much of the Midwest. It can emerge in the fall or spring
and is listed as one of the more difficult weeds to control and
increasingly problematic according to Indiana farmers surveyed
between 1996 and 2000. A characteristic of horseweed is that
it is well adapted to no-till systems typifying the response
of winter annuals to the elimination of preplant tillage and
subsequently infesting summer annual crops. Horseweed generally
emerges in the fall (August – October), over winters as
a rosette, and produces seed the following spring or summer. However,
some researchers reported that horseweed could emerge well
into the spring and that spring emergence should be>considered in
no-till management systems.
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Figure 3. Smilax
leaf, stem and berries. |
Horseweed having an 8 to 13-fold resistance
compared to a susceptible population was discovered in 2000
in Delaware in continuous no-till soybean production. Since
this first report, glyphosate-resistant (GR) horseweed has
also been discovered in Tennessee, Kentucky, Maryland, New
Jersey, Ohio, Indiana, and Arkansas in similar cropping situations.
Biotypes resistant to glyphosate and cloransulam are suspected
in southern Indiana and northern Ohio, respectively. In 2004,
19 counties that had been screened had glyphosate resistant
horseweed/marestial (Figure 4.)
 |
Figure 4. Indiana counties
sampled that had glyphosate resistant horsewee/marestial. |
Source: http://www.btny.purdue.edu/weedScience/2004/articles/updatemarestail04.pdf
