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Understanding “Stacked” Corn

March 22, 2010

This post is all about simplifying the complicated world of corn genetics. There are three levels of stacked corn: single, double, and triple.  Each stack is either: corn borer resistances, corn rootworm resistances, or herbicide resistances.

Single Stacked . . . In the beginning there was Bt corn. This corn has corn borer resistance, specifically the Bacillus thuringiensis protein was introduced into the plant. When a corn borer eats a part of the Bt corn plant, the Bt protein binds to the gut wall. This stops gut function, within hours the gut wall breaks down and gut bacteria invade the body cavity. This ends the corn borer’s life. Bt corn would be considered a single stack variety. Another type of single stacked corn would be Round Up Ready corn without Bt.

Double Stacked . . . This type of corn would include two of the following: corn borer resistance, corn root worm resistance, or herbicide resistance. I find double stacked varieties not as popular anymore.

Triple Stacked . . . These varieties of corn include all of the following: corn borer resistance, corn root worm resistance, and herbicide resistance. Here are the three most popular triple stacked corn varieties.

  1. Yieldgard – Created by Monsanto and introduced into the market in 1997. Yieldgard has changed over the years since its introduction. Currently it provides resistance or tolerance to the following insect pests: Corn Rootworms, Corn Borers, Black Cutworms, Sugarcane and Stalk Borers, Wireworms, White Grubs, Seed Corn Maggots, Early Flea Beetle, and Corn Earworm. In addition Yieldgard is also RoundUp Ready. When a farmer plants corn with the Yieldgard genetics, they must also plant “Refuge” corn. Refuge corn is corn without the insect resistance genetics. The refuge requirement for Yieldgard is 20%. You can calculate refuge by taking the total amount of acres you plan to plant as Yieldgard and multiply by 20%. This number is the amount of refuge corn acres that must be planted in addition to the Yieldgard corn acres.
  2. Herculex – This product was developed by Dow AgroScience and placed on the market in 2006. It was marketed as “entire plant insect protection”. Herculex includes resistances or tolerances to the following insects: Corn Borer, Cutworm, Fall Armyworm, Stalk Borers, Sugarcane Borer, and suppresses Corn Earworm. This variety also includes the Liberty Link genetics, which is a herbicide resistances. Liberty Link protects a crop against Ignite which was formerly known as Liberty. Herculex also features the option to be RoundUp Ready. The refuge required for Herculex is the same as Yieldgard – 20%.
  3. SmartStax – 2010 is the first year this product will be available to the public. It was developed by Dow AgroScience and Monsanto. This variety has both Herculex and Yieldgard genetics, which provide the following insect tolerances and resistances: Wireworm, Seed Corn Maggot, Black Cutworm, Corn Rootworm, European Corn Borer, Western Bean Cutworm, Corn Earworm, and Fall Armyworm. SmartStax also includes RoundUp Ready and Liberty Link genetics. The one huge difference with this variety is the refuge requirement has been reduced to 5%.

This is just a brief over view of these products, if you have any questions post a comment or email me at

5 Comments leave one →
  1. March 23, 2010 9:48 am

    Thanks for the info! I work in the corn industry and didn’t even know all these details!

  2. Chris Schifferns permalink
    October 28, 2011 4:47 pm

    You should update.VT3 pro and rib.soon to be approved for vt2pro. I feel rib corn is important to ensure farmers have non bt corn in the area and enough of it.If pest are present they actually need something to eat besides the bt corn which just kills it.Monsanto and dow are trying to protect there years of work and billions of research on theses traits.the bugs will adapt if we continue to farm as we are.

  3. April 18, 2012 12:00 pm

    Awesome blog 🙂 Very helpful!

  4. April 18, 2012 12:01 pm

    Awesome info. Very helpful because it’s cut and dry 🙂 Thanks!

  5. April 22, 2013 9:39 pm

    Hi there, You’ve done an incredible job. I’ll definitely digg it and personally suggest to my friends.
    I’m confident they’ll be benefited from this

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