UNL CropWatch Dec. 9, 2010: What's New for Bt Corn in 2011

UNL CropWatch Dec. 9, 2010: What's New for Bt Corn in 2011

Dec. 9, 2010

This is one of several timely topics featured at the 2011 UNL Crop Production Meetings to be held at 9 sites this January. See story for details.

Advances in transgenic technology and insect resistance management are occurring at a rapid pace, and it can be hard to keep current. There are now 23 Bt transgenic corn products in five product lines that are resistant to certain insect pests. The mix of traits, target pests, and resistance management requirements vary from product to product and can be quite confusing. To help farmers keep track of the changes to make the best hybrid selections for their farm, Chris DiFonzo (Michigan State University) and Eileen Cullen (University of Wisconsin-Madison) developed a table (below) that presents a recent update of transgenic traits for corn. There are several items to take note of in the trait table.


Seed companies currently offer a total of 23 Bt transgenic corn products in five product lines.
 

Insect Resistance. Six species of caterpillar (European corn borer, western bean cutworm, black cutworm, corn earworm, stalk borer, and fall armyworm) are controlled or suppressed by Bt corn products. Suppressed means that while some of the pest population may be killed by the trait, a significant number will likely survive. If you are expecting a specific pest problem, choose a product that is labeled to control that specific pest, not suppress it.

These Bt products target caterpillars, although not all products control the same group of caterpillars. Beetle-specific transgenic products target corn rootworm larvae; some products target both caterpillars and corn rootworm larvae.

Herbicide Tolerance. Herbicide tolerance also varies among products. Some are only glyphosate or Roundup Ready tolerant, some are only Liberty Link/glufosinate tolerant, and some are tolerant to both Liberty Link/glufosinate tolerant and glyphosate or Roundup Ready. A few products only have some hybrids within the product line that are Roundup Ready/glyphosate tolerant, and one is not herbicide tolerant. Every year corn fields are mistakenly sprayed with a herbicide that they are thought to be tolerant of. Be careful with hybrid selection and remember exactly what traits your hybrid has and where you planted it.

Refuges for Resistance Management


Differences in refuge requirements are based on the biology, behavior, and genetics of the pest, the pest's relationship to the crop, and the relative toxicity of the toxin or toxins within the plant.

Insect resistance management requirements are continuing to evolve. Currently, two basic types of refuge are required — structured and non-structured. A structured refuge refers to the 5% or 20% non-Bt corn plantings farmers are required to plant within, adjacent to, or within ½ mile of the Bt corn field. Non-structured refuge refers to the inclusion of a certain percent of non-Bt corn seed in a bag of Bt corn seed (currently 10%). This is often called refuge-in-a-bag (RIB), and takes the responsibility of planting a separate refuge out of the hands of the farmer.

These differences in refuge size and location can be confusing and beg the question “Why”? Differences in refuge requirements are based on the biology, behavior, and genetics of the pest, the pest’s relationship to the crop, and the relative toxicity of the toxin or toxins within the plant.

Refuge Size

For example, refuge size depends largely on the probability of resistance developing. . The initial transgenic corn hybrids resistant to European corn borer contain one gene that code for the production of one toxin that targets corn borers (e.g. Cry1Ab). This toxin interacts with a specific receptor site in the insect gut. Some of the newer transgenic hybrids contain two genes that code for two different toxins (e.g. Cry1F, Cry1Ab) that interact with two different receptor sites in the insect gut. Either one of these toxins can kill the corn borer. If an insect develops resistance to one of the toxins, it would still likely be susceptible to the other. European corn borers are less likely to develop resistance in corn fields planted with Bt corn that produces two different toxins targeting corn borers than in corn that produces only one corn borer specific toxin. Therefore, the refuge can be smaller for fields planted to corn that produces two toxins targeting corn borers.

Refuge Location

Another example is the difference in refuge proximity to the Bt corn field. For lepidopteran resistant hybrids -- those resistant to corn borer larvae --  the refuge may be up to ½ mile away; however, for coleopteran resistant hybrids -- those resistant to corn rootworm larvae -- the refuge must be in or adjacent to the Bt corn field. In this case, the mobility of the adult insect is the primary reason for the difference. Before they mate, female corn borer moths fly around more than female corn rootworm beetles, so the refuge can be further away for the corn borer resistant hybrids than for the corn rootworm resistant hybrids.

Long-term Value

Many biological, behavioral, genetic, toxicological, and other factors are examined and weighed before specific insect resistance management requirements are established. As we learn more and as new products are developed, insect resistance management will continue to evolve.

Although it does make corn hybrid selection more complex, resistance management requirements will help reduce the chance of resistance developing and help maintain the efficacy of these products well into the future.

Tom Hunt
Extension Entomologist
. Haskell Agricultural Laboratory, Concord
Robert Wright
Extension Entomologist, Lincoln

 


Table 1. Transgenic traits for corn with target pests controlled (bold) or suppressed (italicized), and refuge requirements for the Midwest. Updated November 2010. By Chris DiFonzo (Michigan State University) and Eileen Cullen (University of Wisconsin-Madison)

Trait Group/ Name

Type of Bt

 

Insect(s) 1
Controlled or
Suppressed

Herbicide
Tolerant 2

Refuge % and Location

Agrisure Products (Syngenta; Syngenta + Mycogen/Dow)

Agrisure CB/LL

Cry1Ab

ECB
CEW, FAW, SB

LL

20% – ½ mile

Agrisure GT/CB/LL

Cry1Ab

ECB
CEW, FAW, SB

GT
LL

20% – ½ mile

Agrisure RW

mCry3A

CRW

--

20% adjacent

Agrisure GT/RW

mCry3A

CRW

GT

20% adjacent

Agrisure CB/LL/RW

Cry1Ab
mCry3A

CRW   ECB
CEW, FAW, SB

LL

20% adjacent

Agrisure 3000GT

Cry1Ab
mCry3A

CRW   ECB
CEW, FAW, SB

GT
LL

20% adjacent

Agrisure Viptera 3110

 

Vip3A
Cry1Ab

BCW  CEW
ECB   FAW
WBC
SB

GT
LL

20% ½ mile

Agrisure Viptera 3111

Vip3A
Cry1Ab
mCry3A

 

BCW   CEW CRW   ECB
FAW   WBC
SB

GT
LL

20% adjacent

Herculex Products (Mycogen/Dow and DuPont/Pioneer)

Herculex 1

Cry1F

BCW  ECB
FAW  WBC
CEW

LL
RR23

20% ½ mile

Herculex RW

Cry34/35Ab1

CRW

LL

20% adjacent

Herculex XTRA

Cry 1F
Cry34/35Ab1

BCW   CRW
ECB   FAW
WBC  CEW

LL
RR23

20% adjacent

Optimum AcreMax Products (DuPont/Pioneer)

Optimum AcreMax RW

Cry34/35Ab1

CRW

RR2

10% in the bag

Optimum AcreMax 1

Cry 1F
Cry34/35Ab1

BCW  CRW
ECB   FAW
WBC  CEW

LL
RR2

10% in the bag for CRW and
20% ½ mile
for ECB

Optimum Intrasect Insect Protection

Cry1F
Cry1Ab

ECB  WBC  BCW  FAW  CEW  SB

LL
RR2

5% ½ mile

YieldGard/ Genuity Products (Monsanto)

YieldGard CB  (YGCB)


Cry1Ab

ECB
CEW  FAW  SB

--

20% ½ mile

YieldGard RW (YGRW)

Cry3Bb1

CRW

--

20% adjacent

YieldGard Plus

Cry1Ab
Cry3Bb1

CRW   ECB
CEW  FAW  SB

--

20% adjacent

YieldGard Plus w/ RR2

Cry1Ab
Cry3Bb1

CRW   ECB
CEW  FAW  SB

RR2

20% adjacent

YieldGard VT Rootworm

Cry3Bb1

CRW

 

RR2

20% adjacent

YieldGard VT Triple (VT3)

Cry1Ab
Cry3Bb1

CRW   ECB
CEW  FAW   SB

RR2

20% adjacent

Genuity Products (Monsanto; Monsanto + Mycogen/DowAgro)

Genuity VT Double Pro (VT2P)

Cry1A.105
Cry2Ab2

CEW
ECB   FAW

RR2

5% - ½ mile

Genuity VT Triple Pro (VT3P)

Cry1A.105
Cry2Ab2
Cry3Bb1

CEW   CRW  ECB   FAW

 

RR2

20% - adjacent

Genuity SmartStax (GENSS)(Monsanto)
or

SmartStax (Mycogen)

Cry1A.105
Cry2Ab2
Cry1F
Cry3Bb1
Cry34/
35Ab1

BCW   CEW
CRW   ECB  FAW  WBC

 

RR2
LL

5% - adjacent

 

1 Insect targets: BCW – black cutworm; CEW – corn earworm; CRW - corn rootworm; ECB - European corn borer; FAW – fall armyworm; SB – stalk borer; WBC – western bean cutworm

2 Herbicide traits: GT-glyphosate tolerant; LL-Liberty Link /glufosinate tolerant; RR2-Roundup Ready/ glyphosate tolerant

3 Some hybrids are also RR2 tolerant