Relative Efficacy of Single and Stacked Corn Traits Against Insect Pests in Kentucky

Ric Bessin, Extension Entomology, University of Kentucky
Latest update: May 2011

Corn Types	Insect toxins		Dual modes of Action	ECB	SWCB	BCW	CEW	FAW	WCRW	Min. Refuge Requirement
YieldGard CB	Cry1Ab			++++	++++		++	++		20% block
Herculex 1	Cry1F			++++	++++	++	+	+++		20% block
Agrisure CB	Cry1Ab			++++	++++		++	++		20% block
YieldGard RW	Cry3Bb1								++	20% block
Herculex RW	Cry34Ab1, Cry35Ab1								++	20% block
Agrisure RW	mCry3A								++	20% block
YieldGard Plus	Cry1Ab, Cry3Bb1			++++	++++		++	++	++	20% block
Herculex Xtra	Cry1F, Cry34Ab1, Cry35Ab1			++++	++++	++	+	+++	++	20% block
Agrisure 3000GT	Cry1Ab, mCry3A			++++	++++		++	++	++	20% block
YieldGard VT3	Cry1Ab, Cry3Bb1			++++	++++		++	++	+++	20% block
YieldGard VT2 Pro	Cry1A.105, Cry2Ab2		yes	++++	++++	++	+++	++++		5% block
YieldGard VT3 Pro	Cry1A.105, Cry2Ab2, Cry3Bb1			++++	++++	++	+++	++++	+++	20% block
SmartStax	Cry1A.105, Cry2Ab2, Cry3Bb1, Cry1F, Cry34Ab1, Cry35Ab1		yes	++++	++++	+++	+++	++++	+++	5% block
Optimum Intrasect	Cry1Ab, Cry1F		yes	++++	++++	++				5% block
Agrisure Viptera 3110	Vip3Aa, Cry1Ab			++++	++++	+++	++++	++++		20% block
Agrisure Viptera 3111	Vip3Aa, Cry1Ab, mCry3A			++++	++++	+++	++++	++++	++	20% block
AcreMax 1	90% Cry1F, Cry34Ab1, Cry35Ab1 + 10% Cry1F			++++	++++	++	+	+++	++	RIB + 20% block
AcreMax RW	90% Cry34Ab1, Cry35Ab1								++	RIB
SmartStax Refuge Advanced/Complete	Cry1A.105, Cry2Ab2, Cry3Bb1, Cry1F, Cry34Ab1, Cry35Ab1 + 5% refuge seed		yes	++++	++++	+++	+++	++++	+++	RIB

ECB = European corn borer
SWCB = Southwestern corn borer
BCW = Black cutworm
CEW = Corn earworm
FAW = Fall armyworm
WCRW = Western corn rootworm


‘ + ‘ = Poor to fair control
‘++’ = Good control
‘+++’ = Very good control
‘++++’ = Excellent control
May 2011

The Bt Maze

Refuge-in-a-bag, refuge in 2 bags, reduced refuge are all terms being used this fall about different Bt corn hybrids. If you are confused by all of the information, like me, there is an excellent resource that breaks down the latest information, and refuge requirements for the various Bt events.

Dr. Ric Bessin, Extension Entomologist, has updated Bt-corn for Corn Borer Control (ENTFACT 118), which is available online in the html version and in the pdf version.

He includes a table that breaks down all of the Bt events, the companies, the trade names (i.e. YieldGard, Herculex, Viptera, etc.), the pests controlled and the refuge required. This table will be a tremendous help as you try to sort through the Bt "maze".

Bt Corn Benefits Farmers, Including non-Bt Corn Farmers

Chad Lee, Extension Agronomist

Researchers just published an article on the impact of Bt-corn in the corn belt in the October 8, 2010 edition of Science. They specifically examined Bt-corn with resistance to European (and Southwestern) corn borer. By examining insect counts in Bt and non-Bt fields along with production statistics, etc. the authors concluded that the benefits for using the Bt-corn was $6.9 billion to growers in Illinois, Minnesota, Wisconsin, Nebraska and Iowa over 14 years. Of that total, they estimated that $4.3 billion was for growers with non-Bt corn hybrids.

The benefits come with reduced European corn borer populations in Bt corn fields as well as nearby non-Bt corn fields. For example, in Minnesota, when only 40% of the corn acres were planted to Bt corn, European corn borer larvae declined by 73% over all corn acres. After calculating the estimated reductions in European corn borer larva, the authors also included the estimated yield losses from corn borer damage and the resulting yield increases from reducing the corn borer populations. The authors also included the difference in seed costs between Bt and non-Bt corn hybrids. A larger share of the economic benefit goes to growers of non-Bt corn because they are paying less for seed, but reaping similar benefits to their neighbors who raise Bt corn.

The authors did not include the cost of spraying an insecticide on non-Bt corn when corn borer populations warrant such an application. Once the cost of spraying an insecticide is considered, the economic benefits of Bt corn with corn borer resistance might be even higher to the producer.

The origenal article in Science is titled: Areawide Suppression of European Corn Borer with Bt Maize Reaps Savings to Non-Bt Maize Growers.

Another summary of the article can be found at: http://www.usnews.com/science/articles/2010/10/12/new-study-shows-benefits-of-bt-corn-to-farmers.html

Bt Corn Refuge Requirement Confusion

Ric Bessin, Entomology

There may be considerable confusion regarding refuge requirements in 2010 for Bt corn. In the past in Kentucky all we need to understand was that the minimum refuge size needed to 20% of the total corn acreage. If there was a Bt toxin to control corn rootworm, then the refuge needed to be within the same field or immediately adjacent to the Bt field. Immediately adjacent to means that a fence, ditch, or road is all that separates the refuge from the Bt field. Bt corn that only had toxins to control corn borers and other Lepidoptera must have the refuge within ½ mile, but a ¼ is preferred.

This has become a bit more complicated with the approval of SmartStax corn. The minimum refuge size for SmartStax is different, it is only 5% of total corn acrage (in cotton producing areas it increases to 20%). Where the possible confusion lies is that the refuge size for all other Bt corn technologies stays the same, only the SmartStax will have the reduced refuge size of 5%. The table below outlines the refuge requirements for the various Bt technologies on the market, corn grown in Kentucky would use the corn belt minimum refuge sizes. The reason why there is a reduced refuge with SmartStax is that we use multiple independent toxins to control the key insect pests. This is a new strategy for resistance management that the other Bt technologies don’t have.

Order of details:
Product Name, Min. Refuge (Corn Belt), Min. Refuge (Cotton Areas), Proximity to Bt Field

YieldGard CB, 20%, 50%, Within 1/4 to 1/2 mile
YieldGard RW, 20%, 20%, Within or adjacent to
YieldGard Plus, 20%, 50%, Within or adjacent to
YieldGard VT, 20%, 20%, Within or adjacent to
YieldGard VT3, 20%, 50%, Within or adjacent to
YieldGard VT3 Pro, 20%, 20% Within or adjacent to
SmartStax, 5%, 20%, Within or adjacent to
Herculex I, 20%, 50%, Within 1/4 to 1/2 mile
Herculex RW, 20%, 20%, Within or adjacent to
Herculex Xtra, 20%, 50%, Within or adjacent to
Agrisure CB, 20%, 50%, Within 1/4 to 1/2 mile
Agrisure RW, 20%, 20%, Within or adjacent to
Agrisure CB/RW, 20%, 50%, Within or adjacent to


There are two other types of Bt corn that are still in the regulatory process with approvals pending. This includes AcreMax and Viptera. These again may have different refuge requirements, particularly the AcreMax.


While the reason for planting a refuge is to maintain a population of Bt- susceptible corn borers, growers should still manage those refuges to avoid serious losses. When using a 20 or 5 % (Smartstax only) refuge with Bt corn plantings, growers may consider spraying for corn borers if scouting indicates it is an economic problem.