One of the key issues surrounding the use of Bt transgenic corn hybrids is resistance management. These corn hybrids have been engineered to produce a version of the insecticidal protein from the naturally occurring soil bacterium, Bacillus thuringiensis (Bt), that is toxic to European corn borers and a few other insects. This NebFact discusses the important principles of resistance management for European corn borer and Bt corn and refuge considerations

Echtenkamp, G.W.

Hunt, Thomas E.

English

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Historical Materials from University of 
Nebraska-Lincoln Extension Extension 
2000 
NF00-425 Resistance Management for European Corn Borer and 
Bt Transgenic Corn: Refuge Design and Placement (Revised 
October 2002) 
Thomas E. Hunt 
University of Nebraska - Lincoln, thunt2@unl.edu 
G.W. Echtenkamp 
University of Nebraska - Lincoln 
Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist 
 Part of the Agriculture Commons, and the Curriculum and Instruction Commons 
Hunt, Thomas E. and Echtenkamp, G.W., "NF00-425 Resistance Management for European Corn Borer and 
Bt Transgenic Corn: Refuge Design and Placement (Revised October 2002)" (2000). Historical Materials 
from University of Nebraska-Lincoln Extension. 1826. 
https://digitalcommons.unl.edu/extensionhist/1826 
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. 
NebFact
Published by Cooperative Extension, Institute of Agriculture and Natural Resources,
University of Nebraska-Lincoln
NF00-425
(Revised October 2002)
c-12
Resistance Management for European 
corn Borer and Bt transgenic corn:
Refuge Design and placement
By t. E. Hunt, Extension Entomologist, and
G. W. Echtenkamp, Extension technologist
One of the key issues surrounding the use of Bt transgenic 
corn hybrids is resistance management. These corn hybrids 
have been engineered to produce a version of the insecticidal 
protein from the naturally occurring soil bacterium, Bacillus 
thuringiensis (Bt), that is toxic to European corn borers and 
a few other insects. Corn borer larvae feeding on Bt corn are 
exposed to the Bt toxin at much higher levels than from use 
of foliar Bt insecticides, such as Dipel or M-Peril. Also, corn 
borer larvae are exposed to Bt toxin for much longer periods 
when feeding on Bt corn. Under this high level of selection 
pressure, the threat of resistance necessitates the implementa-
tion of resistance management strategies to prevent or at least 
delay the development of resistance.
An important principle of resistance management for 
European corn borer and Bt corn is the use of refuge plant-
ings. A refuge is any host plant (non-Bt corn, potatoes, oats, 
sorghum, and some weeds) not producing Bt proteins or 
not being treated with conventional Bt formulations. The 
purpose of the refuge is to supply a source of Bt-susceptible 
European corn borer that could mate with resistant European 
corn borer potentially emerging from nearby Bt corn. In 
current resistance management strategies the refuge must be 
non-Bt corn. As a condition of registration by the Environ-
mental Protection Agency (EPA), industry registrants have 
developed resistance management plans to be implemented 
by producers. Specifi c resistance management information 
is a part of each corn seed bag label. Be sure and discuss 
resistance management with your seed dealer.
The EPA has established the following resistance man-
agement requirements.
1. On each farm, growers may plant up to 80 percent 
of their corn acres with Bt corn. At least 20 percent 
of their corn acres must be planted with non-Bt 
corn and treated only as needed with insecticides. 
Decisions to treat the refuge must be based on 
economic thresholds. Conventional Bt products 
(liquids or granules) must not be used on the 
non-Bt refuge.
2. Plant non-Bt corn refuge within, adjacent to, or 
near the Bt cornfi elds. The refuge must be placed 
within 1/2 mile of the Bt fi eld, preferably within 
1/4 mile.
3. If refuge is established as strips within a fi eld 
(Figure 1E), the strips should not be narrower than 
four rows.
Figure 1 presents some general within-fi eld refuge 
confi gurations . Figure 2 presents two examples of how 
you might establish a refuge for a Bt cornfi eld.
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 cornfi elds.
• Strips (Figure 1E) have the advantage of providing 
susceptible European corn borer to all parts of the 
Bt fi eld, but they also have several drawbacks. Strips 
cannot be treated separately from the Bt corn. Harvest 
may be diffi cult if non-Bt strips dry down differently 
than the Bt corn. Also, it is diffi cult to keep track of 
where the strip rows begin or end, so monitoring is 
more diffi cult.
• Do not plant strips narrower than four rows or mix 
seed. This increases the risk of resistance occurring 
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 (30-inch row spacing, 16-row planter).
 A. 80-acre field. In this 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 attain a 20 percent refuge. This border type of refuge has the added advantage of providing 
a buffer around the entire field, which reduces problems associated with pollen drift.
 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. If the pivot corners are planted to corn (approxi-
mately 160 acre total), increase the number to 208 rows. Although this design does not border the field, it does have 
the advantage of intersecting the pivot head in the center of the field. This area often is wet and weedy, providing an 
attractive area for European corn borer moths to aggregate and mate.
Bt corn
Refuge, non-Bt corn
A. 80-acre field B. Pivot irrigated field
NF00-425 — Page 2
N
because European corn borer larvae often move from 
plant to plant. Corn borer larvae that can survive eating 
small amounts of Bt (low level resistance or tolerance) 
can end up on 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 with a 6-row strip size. If you have a 
6-row planter you can achieve a 25 percent, 
6-row refuge by splitting the planter into three units 
of Bt and three units of non-Bt and only strip one- 
half of the cornfield.
• The Bt-susceptible European corn borer from the 
refuge must be present at the same time as possible 
Bt-resistant European corn borer from the Bt corn- 
field. To achieve this the corn hybrid in the refuge 
should be agronomically 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 European corn borer 
moths will be equally attracted to the refuge and Bt 
cornfield. Larvae also 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 attractive to 
European corn borer moths than the corn under irriga-
tion. Remember, the idea is to produce Bt-susceptible 
European corn borer moths.
• The closer the refuge is to the Bt field the better. This 
brings Bt-susceptible European corn borer in close 
proximity to any Bt-resistant European corn borer that 
may survive in the Bt cornfield. Female European corn 
borer generally mate close to where they emerge as 
adults, so having nearby refuge increases the chances 
that a susceptible European corn borer will mate with 
a resistant one.
• You can combine refuge configurations to meet the 
required 20 percent refuge.
A web-based, interactive refuge builder tool is avail-
able at http://agbiosafety.unl.edu/education/refugebuilder/
refugebuilder.htm. Additional information on European 
corn borer management, resistance management, and Bt 
corn hybrids is available through your local County Exten- 
sion Office. This information also is available through the 
UNL Entomology Department Web site located at http://www.
ianr.unl.edu/ianr/entomol/entdept.htm
File under: iNsEcts & pEsts
c-12, Field crops
Revised October 2002
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture
 Elbert C. Dickey, Interim Director of Cooperative Extension, University of Nebraska, Institute of Agriculture and Natural Resources.
University of Nebraska Cooperative Extension educational programs abide with the non-discrimination policies of the University of Nebraska-Lincoln
and the United States Department of Agriculture.


NF00-425 Resistance Management for European Corn Borer and Bt Transgenic Corn: Refuge Design and Placement (Revised October 2002)

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Historical Materials from University of Nebraska-Lincoln Extension Extension 2000 NF00-425 Resistance Management for European Corn Borer and Bt Transgenic Corn: Refuge Design and Placement (Revised October 2002) Thomas E. Hunt University of Nebraska - Lincoln, thunt2@unl.edu G.W. Echtenkamp University of Nebraska - Lincoln Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist  Part of the Agriculture Commons, and the Curriculum and Instruction Commons Hunt, Thomas E. and Echtenkamp, G.W., "NF00-425 Resistance Management for European Corn Borer and Bt Transgenic Corn: Refuge Design and Placement (Revised October 2002)" (2000). Historical Materials from University of Nebraska-Lincoln Extension. 1826. https://digitalcommons.unl.edu/extensionhist/1826 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. NebFactPublished by Cooperative Extension, Institute of Agriculture and Natural Resources,University of Nebraska-LincolnNF00-425(Revised October 2002)c-12Resistance Management for European corn Borer and Bt transgenic corn:Refuge Design and placementBy t. E. Hunt, Extension Entomologist, andG. W. Echtenkamp, Extension technologistOne of the key issues surrounding the use of Bt transgenic corn hybrids is resistance management. These corn hybrids have been engineered to produce a version of the insecticidal protein from the naturally occurring soil bacterium, Bacillus thuringiensis (Bt), that is toxic to European corn borers and a few other insects. Corn borer larvae feeding on Bt corn are exposed to the Bt toxin at much higher levels than from use of foliar Bt insecticides, such as Dipel or M-Peril. Also, corn borer larvae are exposed to Bt toxin for much longer periods when feeding on Bt corn. Under this high level of selection pressure, the threat of resistance necessitates the implementa-tion of resistance management strategies to prevent or at least delay the development of resistance.An important principle of resistance management for European corn borer and Bt corn is the use of refuge plant-ings. A refuge is any host plant (non-Bt corn, potatoes, oats, sorghum, and some weeds) not producing Bt proteins or not being treated with conventional Bt formulations. The purpose of the refuge is to supply a source of Bt-susceptible European corn borer that could mate with resistant European corn borer potentially emerging from nearby Bt corn. In current resistance management strategies the refuge must be non-Bt corn. As a condition of registration by the Environ-mental Protection Agency (EPA), industry registrants have developed resistance management plans to be implemented by producers. Specifi c resistance management information is a part of each corn seed bag label. Be sure and discuss resistance management with your seed dealer.The EPA has established the following resistance man-agement requirements.1. On each farm, growers may plant up to 80 percent of their corn acres with Bt corn. At least 20 percent of their corn acres must be planted with non-Bt corn and treated only as needed with insecticides. Decisions to treat the refuge must be based on economic thresholds. Conventional Bt products (liquids or granules) must not be used on the non-Bt refuge.2. Plant non-Bt corn refuge within, adjacent to, or near the Bt cornfi elds. The refuge must be placed within 1/2 mile of the Bt fi eld, preferably within 1/4 mile.3. If refuge is established as strips within a fi eld (Figure 1E), the strips should not be narrower than four rows.Figure 1 presents some general within-fi eld refuge confi gurations . Figure 2 presents two examples of how you might establish a refuge for a Bt cornfi eld.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 cornfi elds.• Strips (Figure 1E) have the advantage of providing susceptible European corn borer to all parts of the Bt fi eld, but they also have several drawbacks. Strips cannot be treated separately from the Bt corn. Harvest may be diffi cult if non-Bt strips dry down differently than the Bt corn. Also, it is diffi cult to keep track of where the strip rows begin or end, so monitoring is more diffi cult.• Do not plant strips narrower than four rows or mix seed. This increases the risk of resistance occurring 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 (30-inch row spacing, 16-row planter). A. 80-acre field. In this 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 attain a 20 percent refuge. This border type of refuge has the added advantage of providing a buffer around the entire field, which reduces problems associated with pollen drift. 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. If the pivot corners are planted to corn (approxi-mately 160 acre total), increase the number to 208 rows. Although this design does not border the field, it does have the advantage of intersecting the pivot head in the center of the field. This area often is wet and weedy, providing an attractive area for European corn borer moths to aggregate and mate.Bt cornRefuge, non-Bt cornA. 80-acre field B. Pivot irrigated fieldNF00-425 — Page 2Nbecause European corn borer larvae often move from plant to plant. Corn borer larvae that can survive eating small amounts of Bt (low level resistance or tolerance) can end up on 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 with a 6-row strip size. If you have a 6-row planter you can achieve a 25 percent, 6-row refuge by splitting the planter into three units of Bt and three units of non-Bt and only strip one- half of the cornfield.• The Bt-susceptible European corn borer from the refuge must be present at the same time as possible Bt-resistant European corn borer from the Bt corn- field. To achieve this the corn hybrid in the refuge should be agronomically 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 European corn borer moths will be equally attracted to the refuge and Bt cornfield. Larvae also 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 attractive to European corn borer moths than the corn under irriga-tion. Remember, the idea is to produce Bt-susceptible European corn borer moths.• The closer the refuge is to the Bt field the better. This brings Bt-susceptible European corn borer in close proximity to any Bt-resistant European corn borer that may survive in the Bt cornfield. Female European corn borer generally mate close to where they emerge as adults, so having nearby refuge increases the chances that a susceptible European corn borer will mate with a resistant one.• You can combine refuge configurations to meet the required 20 percent refuge.A web-based, interactive refuge builder tool is avail-able at http://agbiosafety.unl.edu/education/refugebuilder/refugebuilder.htm. Additional information on European corn borer management, resistance management, and Bt corn hybrids is available through your local County Exten- sion Office. This information also is available through the UNL Entomology Department Web site located at http://www.ianr.unl.edu/ianr/entomol/entdept.htmFile under: iNsEcts & pEstsc-12, Field cropsRevised October 2002Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture Elbert C. Dickey, Interim Director of Cooperative Extension, University of Nebraska, Institute of Agriculture and Natural Resources.University of Nebraska Cooperative Extension educational programs abide with the non-discrimination policies of the University of Nebraska-Lincolnand the United States Department of Agriculture.

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2822&amp;context=extensionhist

NF00-425 Resistance Management for European Corn Borer and Bt Transgenic Corn: Refuge Design and Placement (Revised October 2002)

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