Battling Weed Resistance – Time For A Community Approach?

If you want to gain control of resistant weeds on your farm, don’t go it alone. Two recent computer simulation studies indicate that local farmers working together can more effectively deal with resistant weeds in the long term compared to taking an “every man for himself” approach.



The simulations were built around using high-efficacy herbicide strategies and the best non-herbicide practices. These simulations also were devised and run by researchers in two distinctly different states – Illinois and Arizona.

Simulation #1: Blocking The Evolution Of Resistance

The first simulation, conducted by a University of Illinois team, focused on control of herbicide-resistant waterhemp at various spatial scales from a 3-square-meter patch all the way up to the county level and beyond.

As farmers took action on weed resistance management across more and more acres, the simulation showed “reductions in the rate of resistance evolution,” says Adam Davis, weed scientist and head of UI’s Department of Crop Science.

“As growers in adjoining areas do the same practices, you begin to affect the long-distance flow of resistance genes,” Davis notes. “Basically, the farmers create a buffer area for each other.”

A key to success for farmers participating in landscape-scale cooperative management is that each operator uses effective and advised practices. Otherwise, resistance can worsen, Davis says.

Best Practices – The Fine Points

For individual farmers within these groups, best practices include “using multiple, effective modes of action applied simultaneously,” Davis stresses.

He adds: “An effective mode of action is one that weeds in your field are not already resistant to.”

Groups of farmers can also team up to push resistant weeds out of their comfort zones by blending more diverse cropping systems into their mix, according to Davis.

“If the market permits, one of the things we can do is to grow some winter annual crops and small grains and create a changing environment that doesn’t favor the growth of common waterhemp, as an example,” he explains. “Simple changes like this in cropping systems can have an enormous impact.

“If you start doing that at scale over more and more of the landscape, you don’t have a place for those resistant alleles (genes) to land.”

While enticing farmers to cooperate with each other could be tricky, Davis can point to an least one precedent.

“Agricultural drainage districts are one of our oldest forms of ‘municipal government’ in Illinois and other parts of the Midwest,” he says. “The early settlers to an area cooperated because it was a public good. Those districts still persist today because they performed really necessary tasks.”

For Davis, it’s not much of a stretch to see farmers organize wide-area weed management entities.

Simulation #2: Bringing In New Approaches

Other best non-herbicide practices for battling weeds include harvest weed seed control practices such as cover crops and narrow windrow burning. Narrow windrow burning has gained attention and acreage in Australia’s fight against resistance.



Out in the future, tools also might include the integrated Harrington Seed Destructor (iHSD) or a similar technology that harvests and/or destroys weed seeds before they reach the soil.

Simulations conducted at the University of Arizona included the iHSD among the tools, and that computer model showed an economic benefit to farmers using seed destruction on a landscape scale.

If farmers collectively purchased and deployed the Australian-developed iHSDs at a landscape-level scale, they could potentially recoup their costs in about seven years, according to the simulations.

“If you can operate it over a larger area, the cost per acre drops,” says George Frisvold, specialist in agricultural-resource economics at the University of Arizona. “So, it’s going to be more economical for bigger operations. Conversely, there is a minimum critical size where it doesn’t make sense.”

The iHSD, which is installed inside the rear of a combine, pulverizes a high percentage of weed seeds gathered at harvest, then it spreads the dusty debris behind the combine.

The iHSD concept continues to evolve and, in fact, a lower-cost model is about to go into commercial production in Australia. Compared to the earliest Harrington Seed Destructor designs, the new system could cost up to 40% less.

IHSDs are becoming more widespread in Australia, where the average farm size is 10,700 acres. That’s a big spread compared to the U.S. In this country, what would be considered a large family farm averages 1,421 acres and a very large family farm averages 2,086 acres.

Weed scientists and ag engineers in several U.S. states are evaluating some variant of the Harrington product line. For example, Arkansas researchers studied the iHSD across 12 common weeds and calculated that it destroyed 99% of the weed seed from 11 of the weed species. With the common cocklebur, the “kill” rate was a still-respectable 97%.

Comparing A Range Of Approaches

For their simulations, Arizona scientists compared the outcomes for two groups of farmers dealing with resistant weeds – those who had medium levels of yield loss and those with lower levels of yield loss.

In these scenarios, farmers with medium levels of yield loss would have the most to gain since they already were taking a bigger hit due to resistance.

The two farm operations were compared in two approaches:

Integrated Harrington Seed Destructor with premium and discount herbicide programs. Premium herbicide programs consisted of glyphosate plus four modes of action at early post, while discount programs consisted of glyphosate plus one mode of action at early post.

Premium and discount herbicide programs without the Harrington Seed Destructor.

Scientists ran the simulations under three operational scales:

  • A single farm – 1,000 acres.
  • Cooperative – 10,000 acres.
  • Cooperative Weed Management Areas (CWMA) – 100,000 acres.

At least 5 preliminary economic findings are worth noting:

#1. Scaling up to landscape level management (Cooperatives and CWMAs) has positive economic payoffs that start early, fluctuate some, but then steadily grow over the long term as farmers manage and prevent herbicide resistance on a wide scale.



#2. Where a farmer sustained medium levels of yield loss to resistant weeds, a cooperative-scale cumulative advantage over 30 years could run $175 per acre, while a CWMA cumulative advantage across 100,000 acres could be $225 per acre over the same time period.

Those dollar amounts are based on yield gains as farmers do a better and more consistent job of controlling resistant weeds. In the model, growers at no time reduce herbicide rates or the number of applications.

The effects on yield add up over the long haul.

Across a 30-year period under a medium-loss scenario, a 1,000-acre farm within a CWMA would accumulate $225,000 more than a 1,000-acre farm going it alone with an iHSD. That’s based on a advantage of $225 an acre times 1,000 acres.

#3. At the cooperative scale, the simulations suggest breakeven at year 8 for a $108,000 iHSD and at year 7 for an $85,000 iHSD. That’s for growers who are sustaining medium levels of yield loss due to resistant weeds. The return outlook is thinner for growers who are in the low range of resistance-related yield losses. As noted earlier, the farmers with the most yield loss also have the most to gain.

#4. More work is needed on farm-scale returns to iHSD adoption. “Returns are a bit iffy at this level,” Frisvold concedes.

#5. Premium herbicide approaches (four modes of action in the early post period) were superior to discount treatments (one mode of action early post) at all scales, with or without iHSD.

Scaling up offers two clear benefits when the iHSD figures into the simulation, according to Frisvold.

  • “One is the cost side – you’re spreading the fixed cost of the (iHSD) machine over more acres,” he says.
  • “Two, the simulations also suggest that you’re doing a better job of controlling the seedbank because you have a bigger block of farmers all doing the right thing.”

Conversely, going it alone has two distinct disadvantages, Frisvold says.

  • First, it’s going to cost more to add something like the iHSD and spread the cost across a minimum number of acres.
  • Also, if a farmer is controlling the seed bank but his neighbors aren’t, “it could all be for naught,” he points out.

While the iHSD is deadly efficient at destroying weed seeds, it’s not the end-all for weed control, Frisvold notes. “You have to look at the iHSD as part of an overall system and what combinations of things will work for you,” he says.

Alternatives might include lower-cost seed destruction methods like narrow windrow burning or narrow windrow composting. Both are approaches Australian farmers are working into their resistance management programs to varying degrees.