Ability Of Insects, Disease And Weeds To Mutate, Change Fact of life

Following recommended practices important to limit or slow down outbreak of resistance.

Published on: Dec 12, 2011

Bt corn borer corn had only been on the market a couple of years when I sat in a presentation by an environmental left-winger who confidently predicted that the trait would be useless in two years. He was sure that farmers would not pay attention to how they planted the hybrids with the new traits, would ignore refuge requirements, and allow the insect to adapt.

Some 15 plus years later, that particular trait is still quite effective. Part of the reason why lies in better stewardship by farmers than the environmentalist expected. That's not to say that everyone complies, because it's common knowledge that some choose not to, although they do so at their own risk should they be spot-checked. Having that refuge out there is important so that if an insect would mutate and be able to live and feed on the corn that's now resistant to it, it would likely mate with a regular corn borer from the refuge rows, and not pass along the trait. At the very least, it would slow it down.

Seed companies have also begun introduction of more products with two modes of action against various pests. The odds of an insect mutating and gaining resistance against one trait become much lower if it has to overcome two very different modes of action that kill the insect in very different ways. SmartStax developed by Monsanto and Dow AgroSciences, with eight genes, has earned 5% refuge and refuge in a bag status from EPA because of multiple modes of action against major pests.

Dave Nanda, crops consultant and director of genetics and technology for Seed Consultants, Inc., will begin a series explaining how various pathogens mutate and develop resistance, citing classic cases in agriculture, in upcoming issue of many Farm Progress publications. If your magazine dos not carry the series any you would like a copy, email: tbechamn@farmporogress.com.

He believes it's important to understand why and how mutations occur, and what farmers can do to limit or slow down their occurrence, since there re recent examples of this activity. The western corn rootworm beetle laying eggs in soybeans in Midwestern states in an example of such a mutation. It originally only laid eggs in corn fields. More recently, resistant weeds to various herbicides, including resistance to glyphosate of several key weeds, has attracted attention. And just last summer, resistance of corn rootworms to one of the early corn rootworm traits was documented in both parts of Iowa and Illinois.

Nanda says such mutations and development of resistance are facts of nature. How long it takes for them to develop depends partly on how farmers follow the rules and guidelines with such practices as leaving enough refuge. These important traits can be maintained for a longer period of time and still be useful, because mutations and development of mutant strains that overcome the resistance, will happen slower if farmers and companies take the necessary precautions, Nanda notes.