Pennsylvania Corn: Which Bt Traits Are Right for Your Operation?

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Now that we have entered autumn, many farmers are starting to think about buying corn seed for 2020. This is the perfect time to reflect upon the value of the transgenic, insect-resistant traits common in so many corn varieties.

These transgenic traits, or Bt traits (Bt is short for Bacillus thuringiensis, the scientific name for the soil bacterium species from which the insect-killing genes were isolated), render corn hybrids toxic to a narrow suite of insect pest species that feed on corn plants.

There are about five transgenic traits currently on the market that target caterpillars feeding on the aboveground portion of plants, while there are four targeting rootworms feeding on roots. The names of these traits and the insects they target can be very confusing, so colleagues at Michigan State and Texas A&M developed a helpful summary document.

These traits (in addition to herbicide-tolerance traits) are partially responsible for the large increase in corn seed costs over the past 30 years. Not surprisingly, some farmers have grown weary of paying so much money for their corn seed and are looking for alternatives. One alternative is growing non-Bt, often called conventional, corn; that is, corn varieties that do not contain Bt traits.

This option is viable because the value of the trait for controlling pests directly relates to the abundance of the pests. If the pest species are not abundant, then the traits have limited value.

For example, corn rootworms are easily controlled in Pennsylvania by rotating corn with soybeans or other crops; therefore, traits targeting rootworms have no value if you rotate your crops annually. The traits targeting caterpillars are similar; if European corn borer is rare in your part of Pennsylvania, then you are getting limited value from the trait that you are buying.

Bt traits targeting caterpillars can also provide some control of fall armyworm and black cutworm, among others, but, again, if these pest species are infrequent visitors to your farm, then the trait is not providing much benefit.

Research that we conducted five or so years ago showed that European corn borer is rare in some parts of Pennsylvania, and in those parts of the state it can be more profitable to grow non-Bt hybrids because of the lower seed costs.

Key to this approach to growing corn is understanding your local pest populations. If you have any non-Bt corn in your area (on your farm or a neighboring farm), walk those fields this fall to see if they have many broken stalks, which can be indicative of corn borer feeding.

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If these fields have little damage, you could plant a small field of a non-Bt hybrid in a rotated field to see how it performs and whether insect pests arrive. If they do arrive in great abundance, you can control those pests with insecticides; if they do not, your corn should grow trouble free and you might realize a greater profit from not spending as much on your seed.

A resource that can help farmers find conventional corn varieties that should work well in your part of Pennsylvania is Penn State Corn Variety testing program, which plants grain and silage varieties around the state to see how they perform.

Each year these trials tend to include some conventional varieties. The results from this annual effort are posted online in December of each year, but you can access results from the previous year on the website of Penn State Extension.

As you well know, farming is a dynamic process with conditions changing annually. If you continually plant Bt seed, but are uncertain of the value, a little experimentation with a non-Bt seed can provide some insight. Chart your path based on your local insect populations. Good luck!




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