Historical Perspective on the Importance of EDRR

Prevention, early detection and expedient control of new invasive plant populations are crucial components of a high-leverage strategy in a landscape-scale invasive weed management program. Such a strategy is largely dependent on thorough and current knowledge of invasive weed distribution in an area. Weed managers may be unable to prioritize search areas or adequately develop prevention plans because information on the spatial distribution of weeds in their management units or in adjacent areas is not broadly available. I sometimes tend to think of early detection-rapid response (EDRR) as a relatively new approach to managing weeds in natural areas: Rejmanek and coauthors discussed the strategy in the late 1990s, Westbrooks and others with FICMNEW emphasized the importance throughout the early 2000s, and the development and increased use of online reporting and verification programs such as EDDMaPS and IPANE have only served to increase our ability to share information on weed distributions. However, in the first significant publication on weed control in Wyoming (The Worst Weeds of Wyoming and Suggested Legislation, UW Ag Experiment Station Bulletin No. 31), Aven Nelson (THE Botanist) discusses the urgent need to control a newly found weed in the state (and it sounds like EDRR to me) –

on Canada thistle:

This is one of the true Thistles and not merely one in name. It has been talked of and written of for years throughout the United States, and as a result is has come to be so dreaded that wherever it appears relentless war has been waged upon it. This, however, has not exterminated it, but has kept it in check. That this commendable vigilance against this foe might not relax, many States have place this in the list of weeds proscribed by law; in fact, it was among the first, if not the first, against which laws were enacted.

This weed is now in Wyoming. The writer found a patch in a stock yard on a farm near Sheridan in July of this year. It was also reported from there, with specimens, in 1895. It is probably that some effort was made to exterminate it at that point, but it is very probable that it has entered the State at other places.

Every one should be on the lookout for this invader, as it is comparatively easy to dig out a few, but when a large area is infested it is a costly undertaking. I use the words dig out advisedly, for it cannot be destroyed by ordinary methods.

It is probably an unrealistic expectation that Dr. Nelson and his cohort of early invasive weed watchers could have eradicated Canada thistle given the technology available to them at that time (we can’t now, either), but what if…? By 1962, early weed mapping efforts had begun to take place in Wyoming and Canada thistle had become widespread throughout much of the state.

Canada thistle in 1962

Canada thistle documented distribution in 1962. From Mitich et al. 1962. Wyoming’s Primary Noxious Weeds, Ag Experiment Station Bulletin 394.

Currently, Canada thistle is estimated to infest more than 250,000 acres in Wyoming (Wyoming CAPS). Distribution, as seen in the map below, has primarily expanded from those locations denoted by Mitich et al. in 1962. Comparing these two estimated distribution maps highlights one of the difficulties in documenting distribution: absence of evidence is not evidence of absence. Some of the locations that appear to be free of Canada thistle in the map below appear as such because data are not available, not because it has been eradicated since 1962.

canada thistle 2011

Township-level distribution of Canada thistle in Wyoming and surrounding counties in 2011. Compiled and presented by Kim Johnson, Fremont County Weed and Pest.

One of the challenges we face in implementing EDRR is the perception, by some, that weeds should reach some minimum level of impact before it makes sense to implement control measures. Investing in finding new infestations before they become established and it becomes no longer feasible to ‘easily dig out a few’ certainly seems worth the effort to me.


  1. Brian,
    Very well said! Especially, the last paragraph- perception is the key word in the paragraph and definitely a challenge key word. Thanks for being so passion about EDRR. js

  2. Wyoming began to recognized weeds a long time ago. The Aven Nelson Quote does not have a date on it, but the Wyoming Legislature passed the Wyoming Canada and Russian Control Act in 1895 which mandated control of both species. Since that time I don’t think a ten year period went by without some significant weed control legislation. All of it was based on the concept that small populations might be eradicated before they could spread and thus there was a benefit to society that justified regulation and subsidy for control.

    Fremont County had one of the first Weed & Pest programs in the state beginning in 1936. There was a board appointed by the County Commissioners who also hired and paid a “weed inspector.” He was usually a full time employee of the county doing road work in the winter. Deputies were hired in the summer. They had a tractor and cultivation tools and went from farm to farm clean cultivating patches of Canada thistle. When World War Two broke out that effort fell by the way side. Weed programs were rejuvenated in 1948 when farmers were facing wide spread invasion of Canada thistle and many other species. Fremont County Weed and Pest has a record of the district purchasing freight car loads (150 Tons) of polyborchlorate, popular soil sterilant on the 1950’s. Crews went from farm to farm spreading upwards of 600# of the herbicide per acre. Both the clean cultivation approach and the polybor did a better job of killing the crop than the Canada thistle. You can believe that here was a lot of conflict between land owners and the county as they destroyed crops in the effort to control thistle. 2,4-D soon became the herbicide of choice but after a decade of use it became clear that there was a lot of selection for resistance in the thistle population. It is interesting to read the old minutes and the county weed reports.

    The greatest challenge of any weed control effort is keep up the pressure. No one has enough money to find and treat every weed. The Nature Conservancy in Montana (Nathan Korb and others)developed a computer model of a weed infestation and used several different approaches to control the weeds. When they started in the middle of the patch, where the weeds are the most dense and maybe easier to treat, even though the cost per acre was low, the weeds continued to spread. Unless they had enough money to treat it all in one year, they lost the battle. Starting on the outside and working in toward the easy acres was more fruitful. They stopped the spread and gradually achieved total control if they had the funds to treat just half of the weeds each year.

    The challenge of an EDRR program is to prioritize where we spend the money. In Fremont County a few years ago we had a pretty good map of Russian knapweed. It infested 450 sections of land. Hopeless? A closer look showed that 200 sections had less than 1 acre. If we focused on those sections we reasoned that we could protect the rest of the section from infestation. Yet that as too many places to go to. So we kept cutting it down. we tried to go to those section with less than 1 acre that were more than 5 miles from the nearest knapweed. It is easy to play these games with a GIS system and Kim Johnson is one of the best at making it work. But, in the end, when you find what you can reach within the limits of your budget and man power you have to stop. Next year you revisit all the treated sites to make sure you have control and then add some new territory. After a few years you decide that for a weed like Russian knapweed EDRR does not work all that well. There are so many weeds and so little time.

    It is interesting to me that Canada thistle is still the number one weed in North America in every poll taken. We have done a great job of selling that weed. However, it is completely naturalized across the continent and is the last weed we should consider in an EDRR effort. We need to leave Canada thistle, Russian knapweed, leafy spurge and field bind weed to biological control and in crop suppression and focus our EDRR resource on things like common crupina where we have just a few plants in the whole state. That will take a significant mapping effort that goes well beyond what most weed districts are doing that the present time. Our current weed programs are justified by the impact these weedy species have on current agricultural productivity and as a result our attention has been directed at reducing that immediate impact in cropping systems. EDRR to some degree will demand that we reduce that emphasis so that we can deal with the economic weeds that will plague us in two or three decades.

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