Ag Instructor Vic Martin: Was Resistance Inevitable?

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Great Bend Tribune

Part I
Published January 12, 2020

The Drought Monitor shows thing essentially unchanged from the previous week.  Barton and Pawnee Counties remain in good shape with most of Stafford County listed as abnormally dry.  Today’s topic may seem a bit early, or too late, and involves pesticide resistance developing in weeds and insects, especially weeds.  Even most people not involved in agriculture are aware of resistance issues that have developed over the last four or so decades with the advent and increased usage of pesticides.  Why be concerned now?  Several reasons including all the challenges with new chemistries and the restrictions being placed on them for one.  And a larger reason is how to we prevent this in the future?  First, let’s look at how it happened.

The best place to start is to define a pesticide, something that kills a pest whether a disease, insect, or weed.  For simplicity, let’s consider herbicides.  Modern herbicides came into their own after WWII.  All have one thing in common, they have a particular mode of action – how they kill the plant.  Some are quite selective and only kill specific species or types of plants while others are nonselective and simply kill plants.  There are many modes of action.  Some target photosynthesis, some cellular respiration, while others affect cell division.  And they target a particular aspect of a given biological process.  They are grouped into different classes based on how they act.

Now let’s look at a selective herbicide, one that only targets certain species or types of plants – say a broadleaf herbicide such as dicamba.  When sprayed on a field of corn it damages and hopefully kills broadleaf weeds like pigweed species.  It is also sprayed on the corn but doesn’t harm the corn even though the corn takes it in.  The corn is able to metabolize, or breakdown, the chemical so it doesn’t damage the crop. 

Roundup ® or glyphosate was originally a nonselective herbicide and was effective on most, not all, plants.  It didn’t matter if it was a broadleaf or grass.  Even before the problems of today, glyphosate wasn’t equally effective on all plants.  Some were harmed but not killed while others were resistant or able to metabolize the chemistry.  By the mid-1990s Monsanto had developed and released Roundup Ready soybean and then corn cultivars which now include crops like alfalfa and canola.  They were able to genetically engineer these crops to metabolize glyphosate. 

Now what does this have to do with weed resistance?  Say an average pigweed plant flowers.  It is possible to produce well over one hundred thousand seeds and these are produced sexually so all the seeds are not identical genetically.  So if you spray them with an herbicide they are susceptible to most will be affected and die.  But out of say 100,000 seeds some will be different enough genetically they will not be killed or only damaged and able to produce seed and pass on that trait.  A very few over time are going to be different enough that they are able to metabolize the chemistry and will essentially be resistant and they reproduce.  So if a producer uses the same chemistry all the time without variation, the result is a shift in the plant population form susceptible to non-susceptible plants.  The plants have evolved.  This is what has happened.  Next week – Part II

Part II
Published January 19, 2020

The Drought Monitor shows thing essentially unchanged from the previous week.  This doesn’t include any moisture received after last Tuesday.  This is good news for the immediate area although mush of Stafford County remains abnormally dry.  February is less than two weeks away so and as day length increases and temperatures start to warm, soil moisture is key for the start of spring growth.  Last week briefly discussed how pesticide resistance occurs when not used properly.  Today, how did we get into this situation and are there success stories is avoiding pesticide resistance.

  • First, we really didn’t know any better and well understand the mechanisms involved. Add in the fact we had very few options fifty years ago for pest management.  And finally, factor in the optimism that something like DDT was a miracle that would lead to a pest few society, eliminate diseases and save food/possessions. We thought we were in a Golden age where chemistry would create a utopia.  Plus the first pesticides seemed to work incredibly well.  It wasn’t until the 1960s and Rachel Carson’s book “Silent Spring” that we started to understand something was wrong.
  • Second, there weren’t many other options early on for insect and weed control.  We could cultivate and burn but genetic engineering wasn’t even on the map and conventional breeding for pest resistance was in its infancy.  Add in the pressure to increase food production for an ever expanding population. 
  • As we started to notice and understand the ecological ramifications of pesticide misuse and pest resistance, we did indeed start to focus on two things.  Integrated pest management and varying modes of action to prevent resistance.  By the mid-1980s we grasped how resistance occurred and what we needed to do.  Then genetic engineering came on the scene.
  • Roundup Ready crops were an example of a failure.  Science knew relying on a single chemistry could lead to resistance issue and many in extension and the USD cautioned about the dangers and the need for a more integrated herbicide approach.  But Roundup was the cheapest option and worked well initially.  It was only after problems started to appear that recommendations were heeded.
  • Bt for control of corn borer is an example of a success story.  It was required that a refuge of non-Bt corn be in every field to insure the genetics for susceptibility remained in the population and it was enforced.  They also worked diligently to insure new and improved Bt technology to further prevent resistance.  Over twenty years later, this is still working.
  • Another success is the adoption of a holistic approach stressing different modes of action, crop rotation, sanitation, and other cultural practices along with improved breeding.

Next week: where do we go from here?

Published January 26, 2020

The Drought Monitor shows things essentially unchanged from the previous week.  This doesn’t include any moisture received after last Tuesday.  The thirty-day forecast from the Climate Prediction Center, released January 16, calls for a fairly good chance of below normal temperatures for most of Kansas and equal chances of above or below normal precipitation.  The three-month outlook predicts a decent chance of above normal temperatures here and equal chances of above or below normal precipitation.  This is good news for getting summer crops planted.  Last week briefly discussed the history of the use and misuse of pesticides, our mistakes with technologies such as Roundup Ready ® crops, and successes such as Bt technology and corn borer control.  Today, where do we go from here?  Can we move forward in a manner that is effective and environmentally sound?

  • First, it would be arrogant to think we will ever win the “war” against pests whether weeds, diseases, or insects.  We learn, adapt, and change and so do they.  To be successful and minimize the damage, producers must change the way they think and approach.  This is why Integrated Pest Management is critical.  We must use a variety of techniques to minimize problems from cultural practices, sanitation, and biological control to pesticides.  We must quit fighting the environment and ecology and learn to work within it and use it to our advantage.
  • Second, at all levels of government there must be a commitment of resources and research invested to develop these holistic approaches.  Producers will need assistance both in terms of money and education to develop these integrated approaches that will allow them to be sustainable economically and ecologically.  This also means public-private partnerships to develop strategies, new genetic engineering products, and new chemistries.  
  • As new chemistries for pest control are developed, it will be vital that they be affordable and that producers are well-educated in their use to avoid the mistakes of the past.  We are getting better in terms of protecting the environment and developing protocols for producers to minimize the chances for resistance developing.
  • The public should be prepared to accept higher food prices as part of an economically and environmentally sound food, fiber, and fuel production system.  Producers currently only receive a small fraction  of the dollars consumers spend on food,
  • Finally, there will be setbacks but they can be minimized by a thoughtful approach that takes the time to fully evaluate new technologies, especially in the area of trying to determine the unexpected consequences of what we are developing.  And we must carefully examine our pest control strategies and plan with climate change in mind.  We are already seeing the effects of climate change on pest pressure and it is a challenge to try and determine the effects of a changing climate on pest pressure.


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