HOW SUCCESSFUL ARE BIOCONTROLS ON KNAPWEED?
When you want to put a spin on some facts, make sure you’ve got some facts to spin.
At the January 9, 2007 meeting of the Boulder County Commissioners, several scientists and County staff
suggested that the diffuse knapweed biocontrols have either not been successful based upon some unspecified criteria, or
that control
has been limited to "relatively small areas".
Commissioner Will Toor asked for a comparison of biological effects versus the other management
actions staff believed were justified. These
need to be summarized in terms of cost-benefit analyses.
Here, I attempt to summarize the data for the ability of biological control insects to contribute
to diffuse knapweed control. Also, I attempt to estimate economic and ecological costs of this activity as well.
This page provides hypotheses and links to studies that provide test of these hypotheses.
If readers find additional information to support or refute anything stated here, please send me an email to that effect.
Hypothesis 1.
Weevils of the genus Larinus, in combination with one or more additional species of insects,
have reduced knapweed to levels where the weed is absolutely of no economic or ecological concern.
While it will remain a roadside weed, it no longer poses a concern to natural or seminatural areas
The Boulder County data are summarized here.
I. Densities of knapweed on the Lastoka property.
Here are the results from 1997 to 2006. There were no plants found on 60 sq,meter, random samples
or on any of the ESCO transects in 2006. (no knapweed plants were found in our samples in 2007, either).
Here are the details from the publications that have appeared based upon Lastoka studies.(for a quick summary, see the
Seastedt et al. 2007 paper)
The 2003 and 2005 publications provide important details.
The soil studies explain why the biocontrol effects can work,and all contain data obtained during the 10 year study.
(additional papers on invasive plant species management, influenced by the Lastoka studies, are available.
The most relevant of these is likely:
Conclusion: In contrast to what is stated in the 2006 Boulder County
Weed report, biocontrols can "eradicate" diffuse knapweed, at least at the scale studied
here.(No, I do not state that the biocontrols can eradicate diffuse knapweed...just
as herbicides cannot eradicate diffuse knapweed. It's a spatial scale issue.)
So, to paraphrase a watergate investigator, "what did he know and when did he know it?"
...when was the County made aware of these data?
Well, in addition to numerous stories in the local press, field trips with managers in 2001
as well as the 2003 publication in Weed Science, there was the direct letter approach
Example of letter submitted to weed manager and commissioners in fall, 2003.
And, to provide evidence that weed kill, without proactive reseeding, results in more weeds,
even when the agent of that kill is biocontrols can be found by reading:
Bush et al., 2007, Ecological Restoration
The only summarized Boulder data also refute BCOS staff's contention that broadcast herbicide spraying in the
absence of reseeding, can produce positive results for native plants. (here's a chance to work up ESCO's Superior and
Associates data that was collected for the city, I believe. Go for it! I admit to already taking a look, and it's very, very
insightful!)
II. Hypothesis 2. These results only occur on "small areas"? The Lastoka site was about 160 acres,
so it would cost perhaps $3200-$6000 to spray once and achieve short-term reductions in knapweed densities? Can this result
be seen elsewhere? The answer is that we've repeated these efforts elsewhere, but why take my word on it?
Let's see what some real weed managers have discovered.
Here's some results from Russ Johnson, Arapahoe County weed specialist. I did a follow-up email with Russ, and he says
that as of 2006 the knapweed has not returned to the grassland, but can be found along the roadside, similar to what we
saw at the Lastoka in 2006.
Results from Arapahoe County, reported in 2004
Here's a well illustrated presentation from Mark Giebel, a weed manager
associated with Highlands Ranch. He got his results in 2006 after releasing insects in 2002 (four years)!
Results obtained in Highlands Ranch by Mark Giebel
And, another 2007 report in from Douglas County:
Is seeing believing? Well, probably not for some. However, I conclude that results obtained at
Lastoka can be obtained (if one tries...) anywhere in the Colorado Front Range. I also point out that the key insect,
Larinus, will likely spread to all sites in the Front Range without further assistance.
We need to get Jody Nelson's DOE-funded results on herbicide effects (no effect after 4 years on the weed, but a
reduction in native cacti), and his insect results, which were looking pretty interesting after 2005!
Here's the 2006 Rocky Flats Report
III. Hypothesis 3. These findings have applications across millions of acres. To test this hypothesis,
let's go to what scientists and weed managers have discovered in California, Oregon, Idaho, Montana, and British Columbia.
George Wooten's epic struggles in Washington make for a great read! George Wooten's work on Diffuse Knapweed
Classic science in Montana Lincoln's Smith's sites in Montana
The longest ongoing study of diffuse knapweed on earth:
Judith Myer's work in British Columbia
and The paper that explains the above abstract,( 30 years of data!!!)
More from British Columbia (see article in newsletter)
Eric Coombs provides a very nice photo of Oregon impacts of Larinus. His
book goes on to say about Larinus, "The weevil has caused dramatic reductions of diffuse knapweed
at sites in Montana, Oregon and Washington." in: Eric Coombs et al.
Biological Control of invasive plants
in the United States. Oregon State University Press.
(note: the fact that this was published in 2004 means that the Larinus impacts were noted some time prior
to the publication date. Books take awhile getting into print.)
A yet-to be published study at military forts in Colorado and Washington
And an anonymous report from Idaho:
"A recent effort at biocontrol of diffuse knapweed in Idaho’s Camas County effectively reduced 8,000 ha (20,000 acres)
of knapweed to minimal levels through the release of the lesser knapweed flower weevil and the knapweed root weevil."
(extracted from: http://en.wikipedia.org/wiki/Diffuse_knapweed#Biological_control on 1/12/07.
I've looked for the original source, but not found it. Is this a 'rural myth'?)
Here's the suspected source, but this report is dated (2002).
Is this, as one scientist suggested "weak science"? I dare anyone to say that to Judith Myers!
Even if the individual studies were flawed for lack of adequate controls (always a problem when the insects eat the reference plots...),
the preponderance of evidence clearly is overwhelming!
Conclusion. Biological control for diffuse knapweed has reduced weeds below economic or
ecological thresholds that would trigger other, more proactive (and costly) management actions throughout
the West. While initial costs for testing, rearing, and distributing the insects were large, Boulder County paid around $0 for this
effort. Now...let's add up the herbicide costs and compare results!
Will these insects pose a threat for native species? After 10 years of observations,
and after extensive literature searches, no effects are known. Since diffuse knapweed declines,
the insects also decline and do not contribute to alterations of the native food webs.
Can we rely on biocontrols for all conditions we will encounter with diffuse knapweed?
NO...There are times when we should probably pull new infestations, and severely disturbed
sites may not clean up with just the insects. Enhanced plant competition via reseeding
is likely necessary to facilitate the insect effect.
Why pay any attention to my 'opinions'?
There is absolutely NO SCIENCE to be found on the following links. DO NOT click on these if science is your life!
Letters rumored to have been sent in response to the hearing
