In 2003, the U.S. Environmental Protection Agency and Monsanto announced the registration of YieldGard Rootworm™ corn containing event MON863. These hybrids express a protein in the roots from the soil bacterium, Bacillus thuringiensis (Bt) that is toxic to larval corn rootworms. This NebFact discusses management requirements, refuge considerations, within-field configurations when using YieldGard Rootworm™

Hunt, Thomas E.

Wright, Robert J

English

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Historical Materials from University of 
Nebraska-Lincoln Extension Extension 
2004 
NF04-594 Resistanct Management for YieldGard Rootworm™ Bt 
Corn 
Robert J. Wright 
University of Nebraska - Lincoln, rwright2@unl.edu 
Thomas E. Hunt 
University of Nebraska - Lincoln, thunt2@unl.edu 
Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist 
 Part of the Agriculture Commons, and the Curriculum and Instruction Commons 
Wright, Robert J. and Hunt, Thomas E., "NF04-594 Resistanct Management for YieldGard Rootworm™ Bt 
Corn" (2004). Historical Materials from University of Nebraska-Lincoln Extension. 1824. 
https://digitalcommons.unl.edu/extensionhist/1824 
This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - 
Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an 
authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 
C-14
NF594
Resistance Management for YieldGard
RootwormTM Bt Corn
By Robert Wright, Extension Entomology Specialist
Tom Hunt, Extension Entomology Specialist
Although the IRM program is similar to those for earlier
Bt corn that targeted European corn borer, there are some
significant differences. This only makes sense, as the biol-
ogy of the corn rootworm is very different than that of the
European corn borer. In particular, rootworm beetles mate
very soon after their emergence and before they begin to
disperse; to encourage mixing of susceptible and poten-
tially resistant beetles, the refuge must be planted closer to
the YieldGard RootwormTM corn than has been required
previously for the Bt corn hybrids used for corn borer
control.
The resistance management requirements for YieldGard
RootwormTM corn are:
•  Growers must plant a structured refuge of at least 20
percent non-YieldGard RootwormTM corn that may be
treated with insecticides (e.g., seed treatments, liq-
uid or granular insecticides) as needed to control
corn rootworm larvae.
•  Growers will not be permitted to apply corn root-
worm labeled insecticides to the refuge for control of
insect pests (either rootworm beetles or other in-
sects, e.g., western bean cutworms, grasshoppers,
etc.) while adult corn rootworm are present unless
the YieldGard Rootworm TM field is treated in a similar
manner.
•  Refuge planting options include blocks in or adja-
cent to YieldGard RootwormTM cornfields or as in-
field strips.
•  External refuges must be planted adjacent to
YieldGard RootwormTM fields.
• When planting the refuge in strips across a field,
refuges must be at least 6 rows wide, preferably 12
consecutive rows wide.
In 2003 the U.S. Environmental Protection Agency and
Monsanto announced the registration of YieldGard
RootwormTM corn containing event MON863. These hy-
brids express a protein in the roots from the soil bacterium
Bacillus thuringiensis (Bt) that is toxic to larval corn
rootworms. Do not confuse YieldGard Rootworm corn with
YieldGard Corn BorerTM corn or any other Bt corn hybrids
that are resistant to European corn borer. The YieldGard
RootwormTM corn hybrids contain a different Bt protein
(Cry3Bb) that is toxic to corn rootworm, but has no effect
on corn borers or any other caterpillars.
As with past Bt corn hybrids, farmers who grow
YieldGard RootwormTM corn will be required to use insect
resistance management (IRM) plans. Corn rootworms have
great potential to develop resistance to management prac-
tices. Nebraska corn growers should be well aware of the
potential for western corn rootworms to develop resis-
tance to insecticides. It has happened twice in Nebraska;
once in the 1950s to the cyclodiene insecticides (dieldrin,
aldrin, and heptachlor), and in the 1990s to methyl par-
athion. People in northeastern Nebraska should be aware
that the northern corn rootworm extended diapause trait
evolved in response to past rotational practices in the
Midwest where corn-soybean rotations were used rou-
tinely for long periods. Northern corn rootworms also
developed resistance to the cyclodiene insecticides in the
1950s.
Similar to past Bt corn resistance management plans,
YieldGard RootwormTM corn requires the use of a refuge
area of non-YieldGard RootwormTM Bt corn. The purpose
of this planting is to provide a local source of rootworm
beetles that have not been exposed to the Cry3Bb Bt
protein. The rationale for this strategy is that beetles
emerging from the refuge area would be able to cross-breed
with any potentially resistant rootworms emerging from
the YieldGard RootwormTM corn field, reducing the likeli-
hood of resistance building.
A. Linear Block B. Bracket C. Border (Perimeter)
D. Block E. Strips (Split Planter)
Figure 1. General types of within-field refuge configurations.
Bt corn
Refuge, non-Bt corn
Figure 2. Examples of refuge design using a 30-inch row spacing, 16-row planter.
A. In this 80-acre field, planting non-Bt corn in 32 row end rows, 32 rows on one side (north-south), and 48 rows
on the other side can provide a 20 percent refuge.
B. 120-130 acre field under pivot irrigation. If only the pivot circle is planted to corn, then a linear block composed
of 160 rows of non-Bt corn meets the 20 percent refuge requirement.
Bt corn
Refuge, non-Bt corn
A. 80-acre field B. Pivot irrigated field
N
•  In addition, the refuge must have a similar cropping
history as the YieldGard RootwormTM corn, that is, if
the YieldGard RootwormTM is planted in ground that
was corn the previous year, so must the refuge.
General management of the YieldGard RootwormTM
corn and the refuge should be similar, e.g., planting
dates, irrigation, fertility programs, etc.
Figure 1 presents some general within-field refuge
configurations. Figure 2 presents two examples of how you
might establish a refuge for a Bt cornfield.
Refuge Considerations
• Linear blocks, brackets, or border refuge plantings
(Figure 1A, B, and C) are relatively easy to plant,
treat, monitor, and harvest. They have the added
advantage of acting as buffer areas between the Bt
corn and non-target habitat or non-GMO cornfields.
• Strips (Figure 1E) have the advantage of providing
susceptible corn rootworms to all parts of the Bt
field, but they also have several drawbacks. Strips
cannot be treated separately from the Bt corn. Har-
vest may be difficult if non-Bt strips dry down
differently than the Bt corn. Also, it may be difficult
to keep track of where the strip rows begin or end, so
monitoring may be more difficult.
• Do not plant strips narrower than six rows or mix
seed. This practice would increase the risk of resis-
tance occurring because corn rootworm larvae may
move from plant to plant. Corn rootworm larvae that
can survive eating small amounts of the Bt toxin
(selecting for resistance) could move to a non-Bt
plant and survive.
• The design for planting strips will depend on your
planter. For example, dedicating three end row units
of a 12-row planter will effectively give you a 25
percent refuge and maintain the 6-row strip size. If
you have a 6-row planter you can achieve the 25
percent, 6-row minimum refuge by splitting the planter
into three units of Bt corn and three units of non-Bt
corn and only strip one-half of the cornfield.
• The Bt-susceptible corn rootworm beetles from the
refuge must be present at the same time as possible
Bt-resistant corn rootworm beetles from the Bt corn-
field to accomplish the desired mixing. To achieve
this, the corn hybrid in the refuge should be agro-
nomically similar (e.g. similar days to maturity) to the
Bt hybrid, planted at the same time as the Bt field, and
managed in the same manner as the Bt field. In this
way the corn rootworm larvae will develop at the
same rates and emerge as adults at the same time.
• Using a neighbor’s cornfield as a refuge is not
allowed because the hybrid selection, planting time,
pest control, and other production activities are not
under the control of the grower planting the Bt corn.
• Planting only non-irrigated pivot corners as refuge
is not recommended because the corn plants in these
areas are significantly different and less suitable for
corn rootworm survival than the corn under irriga-
tion. Remember, the goal of the refuge is to produce
enough Bt-susceptible corn rootworm beetles to
cross breed with those emerging from the Bt corn.
• You can combine different refuge configurations to
meet the required 20 percent refuge.
YieldGard PlusTM
Starting in 2004 a Bt corn which possesses two differ-
ent Bt proteins (YieldGard PlusTM) will be commercially
available. This hybrid has activity against both European
corn borer and corn rootworm larvae. The resistance man-
agement plan can be met in two ways:
1) Plant a minimum of 20 percent of each farm’s
acreage to a non-Bt corn hybrid, within or adjacent
to the YieldGard PlusTM field. In this case the same
non-Bt corn hybrid can serve as a refuge for both
European corn borer and corn rootworm. If refuges
are planted in strips, they should be no less than
six rows wide. All other comments above apply.
2) Alternately, two separate refuges may be planted,
one meeting the European corn borer guidelines
(minimum of 20 percent acres planted to a hybrid
without Bt proteins active against European corn
borer, and refuge within 0.5 mile of YieldGard
PlusTM field), and a second refuge meeting the
requirements for the corn rootworm refuge (mini-
mum of 20 percent of acres planted to a non-
YieldGard RootwormTM hybrid and planted within
or immediately adjacent to the YieldGard PlusTM
field). The possible advantage to this approach is
that a Bt corn active against European corn borer
can serve as the refuge acres for corn rootworms
(since this protein is not active against rootworms),
and a YieldGard RootwormTM hybrid could serve
as a refuge for European corn borer (since this
protein is not active against European corn borer).
In this way, the refuge acres could be protected
from one or the other of the two most important
corn insects in Nebraska, without having to use
planting time or post-emergence insecticides.
File under: INSECTS & PESTS
C-14, Field Crops
Issued March 2004
Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln cooperating with the Counties
and the United States Department of Agriculture.
University of Nebraska–Lincoln Extension educational programs abide with the nondiscrimination policies of the University of Nebraska–Lincoln
and the United States Department of Agriculture.
© 2005, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension.  All rights reserved.
Producer Questions on Resistance Management
Q: I want to plant my refuge acres in the pivot
corners, so I can plant the YieldGard RootwormTM
hybrid where there is the greatest yield potential. Is
this OK?
A: No. The refuge acres must be treated simi-
larly to those planted with the YieldGard RootwormTM
hybrid with respect to agronomic practices, planting
date, fertility, irrigation and previous crop. All these
factors may influence survival of rootworm larvae
and the success of the IRM plan in delaying resis-
tance development.
Q: My neighbor isn’t going to plant YieldGardTM
corn on his farm. Why can’t I use his neighboring
corn fields as my refuge?
A: Each grower is responsible to follow the IRM
requirements for his or her farm. Your neighbor may
change plans and plant soybeans where you thought
corn was going to be planted. Also, the planting dates
may vary greatly between your field and your
neighbor’s, thus decreasing its value as a refuge for
your field.
Q: I buy my hybrids from more than one company.
Who’s going to know if I follow the IRM require-
ments or not?
A: EPA has required the registrant to hire
inspectors who will be visiting grower fields to see
that IRM requirements are being met. EPA also
requires companies to report their sales data. This
information can be combined for all fields in a locality
to check if more than 80 percent of the corn acres were
planted to YieldGard RootwormTM corn.
Q: Why should I follow the IRM plan? If resistance
does occur, the companies can just find another Bt
toxin to add to corn.
A: When you bought the seed, you signed a
contract with the company agreeing to comply with
the IRM plan requirements. Failure to comply may
result in the company not selling these hybrids to you
in the future. Also, we don’t know the characteristics
of resistance that may develop in rootworms. It is
possible that rootworms will develop resistance to
more than one type of Bt toxin depending on the
mechanism of resistance that develops, making it
more difficult to find an effective replacement toxin.
This process, called cross resistance, has occurred
before in western corn rootworm with resistance to
synthetic organic insecticides.
Q: I want to plant my refuge across the road from
my YieldGard RootwormTM cornfield. Is this close
enough to be considered adjacent?
A: Yes, the refuge can be separated from the
YieldGard field by a road or ditch, but not another
field.


NF04-594 Resistanct Management for YieldGard Rootworm™ \u3cem\u3eBt\u3c/em\u3e Corn

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Historical Materials from University of Nebraska-Lincoln Extension Extension 2004 NF04-594 Resistanct Management for YieldGard Rootworm™ Bt Corn Robert J. Wright University of Nebraska - Lincoln, rwright2@unl.edu Thomas E. Hunt University of Nebraska - Lincoln, thunt2@unl.edu Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist  Part of the Agriculture Commons, and the Curriculum and Instruction Commons Wright, Robert J. and Hunt, Thomas E., "NF04-594 Resistanct Management for YieldGard Rootworm™ Bt Corn" (2004). Historical Materials from University of Nebraska-Lincoln Extension. 1824. https://digitalcommons.unl.edu/extensionhist/1824 This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. C-14NF594Resistance Management for YieldGardRootwormTM Bt CornBy Robert Wright, Extension Entomology SpecialistTom Hunt, Extension Entomology SpecialistAlthough the IRM program is similar to those for earlierBt corn that targeted European corn borer, there are somesignificant differences. This only makes sense, as the biol-ogy of the corn rootworm is very different than that of theEuropean corn borer. In particular, rootworm beetles matevery soon after their emergence and before they begin todisperse; to encourage mixing of susceptible and poten-tially resistant beetles, the refuge must be planted closer tothe YieldGard RootwormTM corn than has been requiredpreviously for the Bt corn hybrids used for corn borercontrol.The resistance management requirements for YieldGardRootwormTM corn are:•  Growers must plant a structured refuge of at least 20percent non-YieldGard RootwormTM corn that may betreated with insecticides (e.g., seed treatments, liq-uid or granular insecticides) as needed to controlcorn rootworm larvae.•  Growers will not be permitted to apply corn root-worm labeled insecticides to the refuge for control ofinsect pests (either rootworm beetles or other in-sects, e.g., western bean cutworms, grasshoppers,etc.) while adult corn rootworm are present unlessthe YieldGard Rootworm TM field is treated in a similarmanner.•  Refuge planting options include blocks in or adja-cent to YieldGard RootwormTM cornfields or as in-field strips.•  External refuges must be planted adjacent toYieldGard RootwormTM fields.• When planting the refuge in strips across a field,refuges must be at least 6 rows wide, preferably 12consecutive rows wide.In 2003 the U.S. Environmental Protection Agency andMonsanto announced the registration of YieldGardRootwormTM corn containing event MON863. These hy-brids express a protein in the roots from the soil bacteriumBacillus thuringiensis (Bt) that is toxic to larval cornrootworms. Do not confuse YieldGard Rootworm corn withYieldGard Corn BorerTM corn or any other Bt corn hybridsthat are resistant to European corn borer. The YieldGardRootwormTM corn hybrids contain a different Bt protein(Cry3Bb) that is toxic to corn rootworm, but has no effecton corn borers or any other caterpillars.As with past Bt corn hybrids, farmers who growYieldGard RootwormTM corn will be required to use insectresistance management (IRM) plans. Corn rootworms havegreat potential to develop resistance to management prac-tices. Nebraska corn growers should be well aware of thepotential for western corn rootworms to develop resis-tance to insecticides. It has happened twice in Nebraska;once in the 1950s to the cyclodiene insecticides (dieldrin,aldrin, and heptachlor), and in the 1990s to methyl par-athion. People in northeastern Nebraska should be awarethat the northern corn rootworm extended diapause traitevolved in response to past rotational practices in theMidwest where corn-soybean rotations were used rou-tinely for long periods. Northern corn rootworms alsodeveloped resistance to the cyclodiene insecticides in the1950s.Similar to past Bt corn resistance management plans,YieldGard RootwormTM corn requires the use of a refugearea of non-YieldGard RootwormTM Bt corn. The purposeof this planting is to provide a local source of rootwormbeetles that have not been exposed to the Cry3Bb Btprotein. The rationale for this strategy is that beetlesemerging from the refuge area would be able to cross-breedwith any potentially resistant rootworms emerging fromthe YieldGard RootwormTM corn field, reducing the likeli-hood of resistance building.A. Linear Block B. Bracket C. Border (Perimeter)D. Block E. Strips (Split Planter)Figure 1. General types of within-field refuge configurations.Bt cornRefuge, non-Bt cornFigure 2. Examples of refuge design using a 30-inch row spacing, 16-row planter.A. In this 80-acre field, planting non-Bt corn in 32 row end rows, 32 rows on one side (north-south), and 48 rowson the other side can provide a 20 percent refuge.B. 120-130 acre field under pivot irrigation. If only the pivot circle is planted to corn, then a linear block composedof 160 rows of non-Bt corn meets the 20 percent refuge requirement.Bt cornRefuge, non-Bt cornA. 80-acre field B. Pivot irrigated fieldN•  In addition, the refuge must have a similar croppinghistory as the YieldGard RootwormTM corn, that is, ifthe YieldGard RootwormTM is planted in ground thatwas corn the previous year, so must the refuge.General management of the YieldGard RootwormTMcorn and the refuge should be similar, e.g., plantingdates, irrigation, fertility programs, etc.Figure 1 presents some general within-field refugeconfigurations. Figure 2 presents two examples of how youmight establish a refuge for a Bt cornfield.Refuge Considerations• Linear blocks, brackets, or border refuge plantings(Figure 1A, B, and C) are relatively easy to plant,treat, monitor, and harvest. They have the addedadvantage of acting as buffer areas between the Btcorn and non-target habitat or non-GMO cornfields.• Strips (Figure 1E) have the advantage of providingsusceptible corn rootworms to all parts of the Btfield, but they also have several drawbacks. Stripscannot be treated separately from the Bt corn. Har-vest may be difficult if non-Bt strips dry downdifferently than the Bt corn. Also, it may be difficultto keep track of where the strip rows begin or end, somonitoring may be more difficult.• Do not plant strips narrower than six rows or mixseed. This practice would increase the risk of resis-tance occurring because corn rootworm larvae maymove from plant to plant. Corn rootworm larvae thatcan survive eating small amounts of the Bt toxin(selecting for resistance) could move to a non-Btplant and survive.• The design for planting strips will depend on yourplanter. For example, dedicating three end row unitsof a 12-row planter will effectively give you a 25percent refuge and maintain the 6-row strip size. Ifyou have a 6-row planter you can achieve the 25percent, 6-row minimum refuge by splitting the planterinto three units of Bt corn and three units of non-Btcorn and only strip one-half of the cornfield.• The Bt-susceptible corn rootworm beetles from therefuge must be present at the same time as possibleBt-resistant corn rootworm beetles from the Bt corn-field to accomplish the desired mixing. To achievethis, the corn hybrid in the refuge should be agro-nomically similar (e.g. similar days to maturity) to theBt hybrid, planted at the same time as the Bt field, andmanaged in the same manner as the Bt field. In thisway the corn rootworm larvae will develop at thesame rates and emerge as adults at the same time.• Using a neighbor’s cornfield as a refuge is notallowed because the hybrid selection, planting time,pest control, and other production activities are notunder the control of the grower planting the Bt corn.• Planting only non-irrigated pivot corners as refugeis not recommended because the corn plants in theseareas are significantly different and less suitable forcorn rootworm survival than the corn under irriga-tion. Remember, the goal of the refuge is to produceenough Bt-susceptible corn rootworm beetles tocross breed with those emerging from the Bt corn.• You can combine different refuge configurations tomeet the required 20 percent refuge.YieldGard PlusTMStarting in 2004 a Bt corn which possesses two differ-ent Bt proteins (YieldGard PlusTM) will be commerciallyavailable. This hybrid has activity against both Europeancorn borer and corn rootworm larvae. The resistance man-agement plan can be met in two ways:1) Plant a minimum of 20 percent of each farm’sacreage to a non-Bt corn hybrid, within or adjacentto the YieldGard PlusTM field. In this case the samenon-Bt corn hybrid can serve as a refuge for bothEuropean corn borer and corn rootworm. If refugesare planted in strips, they should be no less thansix rows wide. All other comments above apply.2) Alternately, two separate refuges may be planted,one meeting the European corn borer guidelines(minimum of 20 percent acres planted to a hybridwithout Bt proteins active against European cornborer, and refuge within 0.5 mile of YieldGardPlusTM field), and a second refuge meeting therequirements for the corn rootworm refuge (mini-mum of 20 percent of acres planted to a non-YieldGard RootwormTM hybrid and planted withinor immediately adjacent to the YieldGard PlusTMfield). The possible advantage to this approach isthat a Bt corn active against European corn borercan serve as the refuge acres for corn rootworms(since this protein is not active against rootworms),and a YieldGard RootwormTM hybrid could serveas a refuge for European corn borer (since thisprotein is not active against European corn borer).In this way, the refuge acres could be protectedfrom one or the other of the two most importantcorn insects in Nebraska, without having to useplanting time or post-emergence insecticides.File under: INSECTS & PESTSC-14, Field CropsIssued March 2004Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln cooperating with the Countiesand the United States Department of Agriculture.University of Nebraska–Lincoln Extension educational programs abide with the nondiscrimination policies of the University of Nebraska–Lincolnand the United States Department of Agriculture.© 2005, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension.  All rights reserved.Producer Questions on Resistance ManagementQ: I want to plant my refuge acres in the pivotcorners, so I can plant the YieldGard RootwormTMhybrid where there is the greatest yield potential. Isthis OK?A: No. The refuge acres must be treated simi-larly to those planted with the YieldGard RootwormTMhybrid with respect to agronomic practices, plantingdate, fertility, irrigation and previous crop. All thesefactors may influence survival of rootworm larvaeand the success of the IRM plan in delaying resis-tance development.Q: My neighbor isn’t going to plant YieldGardTMcorn on his farm. Why can’t I use his neighboringcorn fields as my refuge?A: Each grower is responsible to follow the IRMrequirements for his or her farm. Your neighbor maychange plans and plant soybeans where you thoughtcorn was going to be planted. Also, the planting datesmay vary greatly between your field and yourneighbor’s, thus decreasing its value as a refuge foryour field.Q: I buy my hybrids from more than one company.Who’s going to know if I follow the IRM require-ments or not?A: EPA has required the registrant to hireinspectors who will be visiting grower fields to seethat IRM requirements are being met. EPA alsorequires companies to report their sales data. Thisinformation can be combined for all fields in a localityto check if more than 80 percent of the corn acres wereplanted to YieldGard RootwormTM corn.Q: Why should I follow the IRM plan? If resistancedoes occur, the companies can just find another Bttoxin to add to corn.A: When you bought the seed, you signed acontract with the company agreeing to comply withthe IRM plan requirements. Failure to comply mayresult in the company not selling these hybrids to youin the future. Also, we don’t know the characteristicsof resistance that may develop in rootworms. It ispossible that rootworms will develop resistance tomore than one type of Bt toxin depending on themechanism of resistance that develops, making itmore difficult to find an effective replacement toxin.This process, called cross resistance, has occurredbefore in western corn rootworm with resistance tosynthetic organic insecticides.Q: I want to plant my refuge across the road frommy YieldGard RootwormTM cornfield. Is this closeenough to be considered adjacent?A: Yes, the refuge can be separated from theYieldGard field by a road or ditch, but not anotherfield.

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NF04-594 Resistanct Management for YieldGard Rootworm™ \u3cem\u3eBt\u3c/em\u3e Corn

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