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Global Invasive Species Team listserve digest #047
Wed, 3 Nov 1999 14:14:58 -0800 (PST)
--CONTENTS--
1. Preventing resprouts
2. Japanese and Giant Knotweed Alert in Oregon
3. Hydrilla verticillata
4. Buckthorn control results
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1. Preventing resprouts
From: Mike Kelly (MKellySD(at)aol.com)
Girdling sometimes fails because the depth and breadth of the girdle are
inadequate and vascular tissue reconnects and continues transport of water
and nutrients above the girdle. In other cases, as with the buckthorn, it
resprouts from below the girdle. Try girdling and an herbicide such as
100% Roundup or 25% Garlon 4 sprayed into the exposed cambium of the
girdle. This is effective on many trees and shrubs, killing the roots.
Occasionally, some trees/shrubs such as Ailanthus resprout after a cut
stump/girdle plus herbicide treatment. This is apparently due to an auxin
response, where the chemical message to the roots, "don't sprout, don't
sprout" is interrupted with predictable results. If buckthorn responds to
girdle/cut stump plus herbicide this way, switch to the following method.
With plants such as this, don't completely girdle and spray the
circumference. Leave several 1 inch strips of bark/cambium intact. This
appears to prevent resprouting while the herbicide has time to reach the
roots. Generally timing is an issue and this is best done when perennials
have flowered and are beginning to transport resources down to the roots.
Do it before dormancy.
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2. Japanese and Giant Knotweed Alert in Oregon
From: Jonathan Soll (jsoll(at)tnc.org)
We are experiencing a growing and unwelcome presence of Japanese and Giant
knotweed along the Sandy River in Oregon (and I think in most of western
Washington and Oregon). Has anyone with experience with this plant
experimented with repeated mowing/cutting as a control method? Does it
eventually kill the plant if it is sustained over a period of time?
I understand the spray-on chemical options, but does anyone know if
treating the cut stems will
a) kill the plant or
b) at least prevent resprouting for the year?
If so, what is/are the necessary chemical(s), rate and timing?
During 1999 we started testing hand removal via cutting stems 2-5 times.
We also tried direct application of a 50% Glyphosate (Rodeo)solution on
cut stems late this year. Results are not in.
Local herbicide consultants suggest Arsenal or Garlon-3a, if it isn't
right along the water, may be more effective than RODEO.
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3. Hydrilla verticillata
From: Richard Martin (rmartin(at)tnc.org)
We have had some experience with this particularly troublesome aquatic,
which is a widespread pest in Louisiana. The only recourse one has in
infested bodies of water is quite drastic but warrants consideration. On
Lake Martin, a 800-acre lake partially included in our 2,700-acre Cypress
Island Preserve, we have been working with the aquatic weeds division of
Wildlife and Fisheries to combat Hydrilla for the past couple of years.
In a span of less than two years, Hydrilla went from undetected status to
completely covering the surface of over 200 acres. The effects of
Hydrilla infestation are mixed, heavy infestations can result in local
extirpation of native aquatics, but the increased surface area apparently
supports higher densities of invertebrates and provides excellent cover
for young fishes. For those of you that like American Coots, the density
of Coots increased by several orders of magnitude with the establishment
of Hydrilla.
The only control method that has limited long-term effects is to rapidly
increase water depth by approximately 4 feet after Hydrilla has "topped
out" at the lake surface. This was apparently the reason for the near
total removal of Hydrilla from Caney Lake in Northern Louisiana.
However, if you are unable to manage water depth, you must result to
chemical and biological control. Mechanical removal will have no effect.
At Lake Martin, Wildlife and Fisheries first treated the infested portion
of the lake with granular Sonar (Fluridone), which significantly knocked
back Hydrilla as well as any other aquatics it came in contact with. As
with any aquatic herbicide, this is best used in areas with minimal water
exchange so as to limit non-target mortality. Once the herbicide had
taken effect, LDWF introduced grass carp (Ctenopharyngodon idella) at the
rate of 4 per acre of lake surface (3,200 total). Grass carp are
herbivores that apparently prefer Hydrilla, but will consume any aquatic
if Hydrilla density is greatly reduced. The initial results are quite
positive from an invasive weeds perspective, the results to native aquatic
plant communities remains to be seen.
The grass carp released were triploid, and presumed sterile. However,
recent studies of "sterile" grass carp indicate that nearly 2% are in fact
fertile. Thus, if grass carp are not already established in your region,
you would not likely want to take this approach. Grass carp breed in
larger, flowing rivers and we had recent inventory data that recorded
grass carp larvae in the watershed.
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4. Buckthorn control results
From: Barry Rice (bamrice(at)ucdavis.edu)
Ana Ruesink's recent report on attacking buckthorn reminded me that the
best way to approach weed control is to integrate new management
approaches with "tried and true" methods developed by other managers.
Don't forget to contact people who have already been battling your foe
weed species. The weed reports have this contact information for this very
reason!