For Release January 25, 2000

AGRI-VIEWS
by Chuck Otte, Geary County Extension Agent

Prior to the advent of Bt corn and Roundup Ready soybeans, the only time that we had heard about pesticide resistance was with fly tags on cattle and a few weeds in western Kansas. Now we not only need to be aware of pesticide resistance (meaning either insecticide, fungicide or herbicide) to keep these tools available, but to also stay in compliance with federal regulations. For the purpose of this discussion we will sidestep all the questions surrounding genetically modified organisms (GMOs) and simply accept that for the 2000 cropping year they will be planted on at least some of the local acres.

Pesticide resistance, in insects or plants, is not usually something that spontaneously evolves. There is a very small fraction of any population that has a gene that is resistant to a certain pesticide. If this gene is a paired with a susceptible gene then the organism is usually susceptible to the pesticide. But if the gene is paired with another resistant gene the individual will be resistant to that pesticide. But since, in a natural population, the presence of this resistant gene is so low it keeps getting diluted with all the susceptible genes in the population so it stays at a low level.

Now we come along with that pesticide that the gene is resistant to. This happens to be a very good pesticide and very quickly kills nearly all of the susceptible organisms. In a matter of a couple of years the resistant gene suddenly becomes the majority and the few organisms left all have resistance. As these few organisms mate, the majority of the offspring is also resistant to the pesticide. In just a few years we have developed a population that is resistant to the common control that was once used. This is a simplified version of how pesticide resistance develops. In some cases it has taken less than five years, in some cases it may take over ten years.

In the real world, cases of pesticide resistance have been surprisingly few. The choice of pesticides has been broad and the population of what we were trying to be controlled has been large enough that it has been difficult to create a resistant population. Insects, because they are more mobile than plants, have tended to be more likely to develop a resistance problem. But resistance has been documented in insects, diseases and weeds. Some of the resistance problems in infectious organisms affecting humans has been very well documented.

With the development of corn with built in corn borer killing ability, Bt corn, it does expose a high proportion of the corn borer population to a selection pressure. Therefore, the EPA has recently released it’s requirements for refuge areas and amount of non-Bt corn to be planted. In Kansas, at least 20% of a producers corn acreage must be in non-Bt corn hybrids. In the southern states it is 50% of a producers acreage. The actual details are much lengthier, see me for details.

There are no requirements for refuge areas, etc. with Roundup Ready crops. But to be right honest, I would tend to treat this is a similar fashion. Leave a couple of rows around the edges of fields unsprayed. Sure, it’ll be weedy where everyone can see. But it will make sure that there is a lot of pollen from susceptible weeds floating around.

This technology may very well not be for everyone. But if we don’t manage it right, it won’t be long before it isn’t available or isn’t working for anyone.

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