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Purity of Liberty Link seed
by Bob Hartzler
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June 6, 1997 -- As we enter the era of herbicide resistant crops, one of the issues that may come up is whether all the seed in a bag contain the trait that provides resistance. In the case of Liberty Link corn, AgrEvo will only certify seed lots as Liberty-Link if 97% of the population carries the trait providing resistance to glufosinate. This means that up to 3% of the corn crop might not be resistant, and therefore would be killed by Liberty if it was applied to the field. The question may arise whether losing 3% of your stand is a significant issue?

Mike White, extension field specialist in southwest Iowa, recently reported a situation where this issue has caused a problem. A farmer planted Liberty-Link seed at approximately 27,000 seeds per acre, and ended up with 20,000 plants emerged. The Liberty treatment killed some corn plants, as it is likely to do, and knocked the population down to a little over 19,000. The grower was unhappy with this stand loss and is questioning whether to use Liberty on the remainder of his fields planted to Liberty-Link hybrids. Would switching herbicides be an appropriate management decision?

The accompanying graph is a summary of ISU research investigating the relationship between corn population and yield. Between 22,000 and 18,000 plants per acre, there is approximately a 1.25% yield loss for every 1000 plants lost. In the situation described above, the application of Liberty would have killed a maximum of 600 plants (3% of 20,000). According to the data presented in the graph, this stand loss would result in a yield loss of 0.75%. Obviously, any stand loss is undesirable, but in most situations, a 3% loss will not result in a significant reduction in yield potential. Also, it is likely that most seed lots have less than 3% non-transformed seed, so the 3% loss represents a worse case scenario.

Although the potential loss of stand probably should be considered when deciding whether to use Liberty, the effectiveness of Liberty on the weeds present in the field and the cost of Liberty in comparison to other options should be more important in the decision process.

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
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Common chemical and trade names are used in this publication. The use of trade names is for clarity by the reader. Inclusion of a trade name does not imply endorsement of that particular brand of herbicide and exclusion does not imply nonapproval.