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.
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.
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.