OSU Extension, Darke County...
Resistance of Corn Rootworm to Bt
Corn
Discovered in Iowa
By Justin Petrosino, ANR Extension
Educator
August 10, 2011
After
receiving complaints from
farmers, researchers at Iowa State University launched an investigation
into
several problem fields in Iowa. Farmers complained of heavy rootworm
feeding in
fields that were planted with a corn hybrid with Bt protection for
rootworm.
Corn with Bt protection has a gene from the bacteria Bacillus
thuringiensis that
confers resistance to insect feeding.
Insects
were collected from problem
fields across the state of Iowa along with samples from fields with no
reported
problems. The rootworm larva were grown in controlled conditions in the
lab and
were fed roots from plants expressing a single Bt trait (Cry3bb1,
Cry34/35ab1)
or no Bt trait (control).
The
insect larva from the control
fields were not impacted by the non-Bt trait corn hybrid and were
controlled
with all Bt traits, as one would expect. The rootworm larva from the
problem
fields were controlled with the Cry34/35ab1 trait but not the Cry3bb1
trait.
This is the first reported case of coleopteran (beetle) resistance to
Bt
traits. The Cry3bb1
trait is found in
YieldGard products.
An
investigation into practices that
led to resistance shows a similar story to other cases of pests
developing
resistance to a control measure. Problem fields were planted to
continuous corn
for at least three years with only the Cry3bb1 trait for rootworm
control. The
research paper that reported the insect resistance also cited that only
50% of
the needed refuge was planted.
Thankfully
for Darke County farmers
this problem is currently only identified in Iowa. To avoid a similar
problem,
Darke County farmers need to heed several management recommendations.
First,
crops should be rotated to decrease the pressure of the Bt trait on the
insect
population. If corn will be planted for more than one season in a
field,
farmers should rotate Bt traits or plant a hybrid with multiple traits
for
rootworm control. Secondly, the needed refuge should be planted to help
dilute
any resistance that may be present in an insect population. Thirdly
farmers
should never rely on a single management practice for a pest problem.
For more
information on the resistant rootworm biotypes visit the CORN
Newsletter at
http://corn.osu.edu/ or the OSU Agricultural Entomology at
http://entomology.osu.edu/ag/.
A similar problem with resistance
to a
management tactic is present in Darke County. Among other weeds like
marestail
and giant ragweed, the weed waterhemp is confirmed in Darke County to
be
resistant to both glyphosate (Roundup, Cornerstone, Buccaneer, etc…)
and ALS
inhibitor herbicides (FirstRate, Classic, Synchrony). In other states
waterhemp
is resistant to other herbicide families including the triazines
(atrazine and
simazine), PPO inhibitors (FlexStar, Cobra), and the HPPD and PD
inhibitors
(bleacher herbicides like Balance, Command, and Callisto). A single
plant in
Illinois was identified as resistant to glyphosate, triazines, ALS, and
PPO
inhibitors. This weed has the potential to increase a resistant portion
of the
population quickly if a single herbicide is used year after year. To
learn
about waterhemp and to have a general discussion of weed management,
visit the
OSU Extension, Darke County, research site at the corner of Brock
Cosmos and
Arnett Roads near Rossburg on Tuesday, August 16, at 7pm. Signs will be
posted
to direct you to the site from the intersection. The site is about a
mile east
of Route 49 on Brock Cosmos or two miles west of Route 118. The site
hosts 28
different herbicide programs in corn and soybean crops. There is no
need to
RSVP for the event but more information is available by calling the
Extension
Office at (937) 548-52 |
