Ag Instructor Vic Martin: Weed Control Wisdom?

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Great Bend Tribune
Part I

Published July 26, 2020

The six to ten day outlook (July 28 to August 1) indicates normal to below normal temperatures and above normal precipitation.  Good news for summer row crops.  Looking out eight to fourteen days (July 30 to August 5) indicates normal to above normal temperatures and below normal rainfall.  The drought monitor indicates receding dry and droughty soils conditions for our area. The overall outlook for August through October is for above normal temperatures and below normal rainfall for our area.  Drought is holding on in Southwest Kansas with severe and extreme drought along the border.  Much of Southeast Kansas is now in moderate drought.  Good news for our area as corn kernels are developing, milo is starting to head out, and soybeans are starting to fill pods and continuing to bloom.  Weed control is certainly a topic currently with controlling weeds in wheat and in summer row crops and the problems ahead.  Instead of specifics, let’s speak generally about how to attack weeds in crops.

First, we are having the problems we have as we overused the same modes of action, how the herbicide kills the plant.  So why do we have weeds in the first place?

  • Agricultural production isn’t a “natural” ecosystem.  The next time you are out in the country, try to find some native prairie to look at that hasn’t been overgrazed.  You will notice it’s a bit messy.  It’s not neat and orderly and all the niches available are filled; i.e. there isn’t a lot of bare ground.  Contrast that with row crop production where plants are in rows of varying widths where we keep plants from growing between the rows.  To sound a bit poetic, nature “fights” against that.  It seeks the lowest energy input state which is more like native prairie.  It tries to fill in that bare space.
  • It takes energy inputs - manual labor, machinery, fertilizers, and pesticides to maintain this “unnatural” system.  Add to that mix the fact we breed crop plants for optimum production under these conditions.  Plants that are introduced, not native to our soil and climate conditions.  We have little genetic diversity in our crop plants which is in many ways a good thing as we want a uniform product which moves through the growing season together.  Contrast this with weeds, non-crop plants, that have much more genetic diversity and aren’t nearly as synchronized.  There seeds many germinated over several years for example.  They are better adapted to the conditions and better competitors for resources.  Many can spread and reproduced in ways other than seed.
  • Finally, for today, add in the environment we create for our crop plants – optimum fertility, perhaps irrigation, etc.  These conditions are also optimal for weeds which tend to be more vigorous and can often outcompete crops and are better able to withstand stresses in our area.  And they are well-able to take advantage of all that open space between crop rows and produce seed under less than optimal conditions.
  • Perhaps one last item – nature is quite adaptable whether with weeds, insects, or diseases.  So as we find ways to control weeds, nature adapts and overcomes them if we aren’t very careful.

Next week – what to do about this problem.

Part II

Published Aug. 2, 2020

The six to ten day outlook (August 5 to 9) indicates below normal temperatures and normal to above normal precipitation.  Good news for summer row crops.  Looking out eight to fourteen days (August 7 to 13) indicates normal to below normal temperatures and above normal rainfall.  The drought monitor indicates receding dry and droughty soils conditions for most of Kansas and this doesn’t include any rains since last Tuesday.  Corn is in excellent shape with this moisture and more moderate temperatures to fill well.  Milo and soybeans ha7ve also benefitted greatly but only time will tell the whole story.  Last week, we discussed why we are dealing with the weed control issues we are.  Today, what can we do to overcome/manage this challenge?  We will focus on the best agronomic practices without other important concerns such as landlord-tenant arrangements, bankers and loans, etc.

First, there is no, one answer, but a variety of cultural practices.  The Term is IPM (Integrated Pest Management) and it considers and uses all possible tools available, including herbicides.  Second, there is no one answer since soils vary, the nature and extent of weed problems vary, and the climate across Kansas in terms of rainfall, growing season and other factors vary greatly.  Options increase from the Colorado border as you move east.  Finally, we aren’t considering economic variables and other items producers must take into account.

  • This may seem obvious, but it is key to understand the weed problems in each field, this includes the species, identifying the extent of weeds pressure, and where possible herbicide resistance.  Along with that, knowing what herbicides have been used over past years.
  • While not easy, with diligence and some luck it is possible to decrease weed pressure over time.  However, this requires very intensive management and isn’t cheap.
  • Since herbicides are a fact of life in crop production for almost all operations, rotating modes of action is critical.  Pre-emergence herbicides should be included in crops like corn, milo, and soybeans in particular.  GMO crops allowing for the use of glyphosate are fine as are others such as dicamba and 2,4-D tolerance but producers still must vary modes of action.  The answers aren’t cheap but necessary to get a handle on this.
  • Producers need to go back to the pre Roundup Ready days and work to control grasses in broadleaf crops and broadleaf weeds in grass crops.  Again not as cheap as what we are currently doing but necessary.
  • As much as is possible and practical – crop rotation will help.  This depends on soil type, climate, and markets.  It does help, especially since the next bullet point also helps.
  • Eliminate as much tillage as possible.  This is difficult as tillage is still a major weed control tool but disturbing the soil as little as possible and allowing a reasonable amount of residue on the soil surface helps decrease weed pressure over time.  Or if tilling, and depending on the situation, planting and then killing and leaving a cover crop in place to cover the soil can greatly help.  This isn’t for every situation.
  • The best weed control is an actively growing crop so doing everything possible to provide optimum crop growing conditions, i.e. all cultural practices from planting rate, row spacing, and fertility matter more now than ever.

There is much more but we are out of space.  This is a problem that must be addressed as we must continue to increase per acre production for a growing world population.






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