Weed Resistance Management – 6 Ways Your 2017 Planning Starts Now

It’s not too early to start thinking about herbicide resistance management in 2017. Now is the time to:

  • Begin evaluating this year’s successes and failures in terms of weed control. Those results provide a starting point for planning next year’s strategies.
  • Pinpoint additional in-season steps that minimize resistance development next season. These are the “extra” steps that you can take after the last planned herbicide applications go out in the current crop.

Here are 6 steps worth considering:

#1. Take No Prisoners When It Comes To Resistant Weeds

No matter the geographic location, the first reaction to finding weed resistance is usually denial. And, of course, denial means a delayed reaction so a few escapes left unattended can grow into a complete infestation either by the next season, or if you’re lucky, two seasons later. 

Weed populations will evolve to fit the environment when the same herbicide has been used season after season with little or no backup from other chemistries and modes of action.

Pulling or hoeing those weeds won’t eliminate resistance in a given field. By the time you notice those first escapes, resistance is already lurking in the soil among seeds that will sprout later in the season or next year. But taking out escapes early on goes a long way toward easing problems later.

Weed scientists regularly cite the fact that a full-grown female Palmer pigweed can generate a million or more seeds in a given season. Waterhemp, likewise, propagates at nearly that same level.

So, every weed that doesn’t make it to maturity represents thousands of seeds that won’t germinate in the future.

Time spent pulling or hoeing weeds at the first sign of resistance also might reduce the risk of having to bring in chopping or roguing crews to clean up bigger messes in the future. Those salvage operations cost plenty. In parts of the country, it’s doubtful you can find that kind of labor at all.

If seeds already have formed on escaped plants, pull or chop the weeds and carry them to the side of the field, then pile the plants together and burn them. If weeds are mature enough that seeds could drop from the heads, place the plants in a large plastic bag before hustling it out of the field to avoid  spreading more seed in the process. Extreme problems call for extreme measures.

#2. Watch The Edges For Resistant Weeds

Control resistant species wherever you find them – on field edges, in ditches, in equipment yards. It doesn’t take much for an implement or combine to inadvertently pick up viable seeds on a turnrow and then carry them deep into a field.

One north Alabama crop consultant told us this year that marestail was so prolific this season that he actually found it emerging in gravel driveways. That seed got there somehow.

Consultants in the South also have said that glyphosate-resistant Italian ryegrass seemed to start along roadsides where highway crews made repeated cleanup sprays with glyphosate for several years. From there, the grass gained resistance and crept onto turnrows where it could be mechanically distributed into the rows during common field work.

Fence lines and waterways also can harbor resistant populations. Where herbicides are flown on, watch for escapes near or under utility lines. As the plane pulls up, that last few feet of spray might dissipate faster since it was released higher above the ground. Any weeds along those field edge might receive a sub-lethal dose and live to produce seed.

#3. Practice Good Weed Sanitation

Clean your equipment between fields or farms – especially combines – to ensure that resistant weed seeds won’t be carried to other fields. Admittedly, weed scientists have stressed that point since the dawn of glyphosate resistance, but it bears repeating.

Beyond that, be careful what you buy, equipment-wise. Even a seemingly new piece of machinery might have been sent out on a demonstration run a time or two. Did a combine pick up herbicide-resistant seeds while away from the dealership? Did the dealer make a real effort to clean up the machine, aside from a superficial wash job?

This is a bit like preaching the virtues of safe sex. Any piece of machinery that’s been in anyone else’s fields before you buy it could bring along problems associated with that acreage, known or unknown.

One Extension weed scientist in a Midwestern state said off the record that he quietly discourages his farmers from buying combines from certain Southern states because the machines might bring along resistant Palmer pigweed or marestail.

If you do buy used equipment – even from a guy down the road – thoroughly clean it, particularly any machinery related to harvest.

#4. Evaluate 2016 Herbicide Results

As the season progresses, determine how well herbicides held up and to what extent escapes appear.

Take notes, either on paper or electronically. Do not rely on your memory or what your employees or crop advisor might recall.

  • Keep precise records on treatments, application dates, materials used (including adjutants and surfactants) and rates. Also jot down nozzle sizes, weather conditions and anything else that relates to how well a given herbicide performs against targeted species.
  • Map out fields and highlight areas where escapes were apparent. List any follow-up work, too, things like chopping, pulling, spot spraying.

While all this may seem a bit like busy work, it gives you a clear chance to look for patterns and trends as you plan the next year’s crop mix, rotation and the seed technologies you might use.

#5. Look For Late Weed Escapes

Control late-season flushes that emerge following harvest, especially in corn. This might be done with tillage, herbicides or both. Again, map them out. Keep an eye out from the combine, as well.

If you’re mulling over whether to buy a drone, this is another potential use, especially to get above corn to detect escapes not easily seen from the turnrow.

#6. Learn More About Herbicide Resistance

After harvest, make it a point to absorb new information about herbicide resistance and management. Compared to the last decade when the first inklings of resistance were surfacing, far more is known now about minimizing the chance for resistance.

Look for meetings that include resistance management topics or sections. Also, check Land Grant university sites for on-line learning experiences, including webcasts and video presentations. This topic won’t go away and as the frequency of resistance expands northward, plenty of research and practical information will be available.

Unless resistant seeds were inadvertently deposited in your field, problems that develop are likely home grown. It took several years for resistance to develop and gain enough momentum to become obvious. By now, resistant weeds already have deposited their seeds in your soil where they can lie dormant for years.

Over the winter begin formulating a long-term plan that includes logical tankmix combinations, crop rotation and possible technology rotation.