Producers that have ordered their NK corn will have noticed that they were required to sign a separate IRM (Insect Resistance Management) Stewardship Agreement when ordering Bt corn. This form is due diligence for NK in helping to ensure that everyone is playing by the rules with refuge management. Once you sign the IRM Agreement it will be on permanent file and you will not have to be bothered with the forms again.

I have found this past year that most producers do not have a problem with signing the form and these producers diligently follow the 20% refugia guidelines. However, there is always a small percentage that questions the need and argues that they do not want to have reduced yield on 20% of their acres because they see a yield advantage to their Bt corn. The purpose here is to help explain the due diligence of using refugia hybrids and why implementing an IRM on your farm is in your best interests.

First and foremost seed companies and affiliations do not want a development of resistance in corn borer to the Bt events that we have available to us now. The two most prevalent events are; 176, which you would find in Max 23, Max 357, Max 86 and Bt 11 commonly called Yield Guard that is in all of the newer NK hybrids. In a nutshell, if resistance develops to these two events than we will lose the corn borer protection provided by the Bt corn. The importance of this is that at the present time there are no other Bt events being created to replace what we have now.

Industry has recommended that if you are growing Bt corn a minimum of 20% of your corn acreage needs to be planted with a non-Bt hybrid within approximately 1000 feet or ¼ mile or 400 metres (whichever language you speak) of the Bt corn. The refuge can be planted in whole blocks or in strips that are a minimum of 6 rows. The important item is to have the non-Bt corn within the distance requirements of all of the Bt corn. It is simply not good enough to rely on your neighbour to grow the refuge for you even if you know for sure that they will grow non-Bt corn. If the furthest edge of your field containing the Bt corn is greater than 1000 feet that plan simply will not work within the guidelines.

Why these guidelines? European corn borer moths are not strong at flying and research shows that the majority of adult females will stay within 400 metres of where they emerge. In any population of corn borer there are a rare few that will have a natural resistance to the Bt protein. The key is to have a mix of these resistant borers reproducing with ones that have no-resistance to the Bt proteins. In essence the Bt proteins that they ingest from the plant can then control the offspring. If there is only Bt corn to feed on the fear is that we will create an environment in which the naturally resistant corn borers will reproduce only amongst themselves because the non-resistance borers will have died. This will then help to proliferate the population of resistant corn borers and making the Bt corn that we now have available utterly useless against corn borer infestation. Instead of having a yield lag on just 20% of corn acres in higher incidence corn borer areas we would have nothing to protect the other the entire crop. Although this is a compressed way of looking at the science behind insect resistance management I hope it helps to point out the importance of maintaining at least 20% of your corn acreage to refugia hybrids.

More detailed information can be found in “A Grower’s Handbook, Controlling European Corn Borer with Bt Corn Technology”.

Ryan Hurley