Re: CULT: toxic Canada thistles?

I searched the web for Cirsium arvense (Canada thistle) and found nearly
8,000 references.  I then searched within those for allelopathy (production
of substances by one plant that limit the growth of another).  All the
results were about the effect of allelopathy of OTHER plants on Canada
thistle.  There was no mention of allelopathy  by this plant toward others.

Which does not mean that it does not occur.  However, CT has an enormous
root system.  A single plant may send roots more than ten feet in all
directions, and as much as 15 feet deep in suitable soils, and consist of
hundreds of aboveground shoots.

So it seems to me possible that even though the thistle shoots in the iris
clumps were small, the iris roots may have been unable to compete with the
thistle root system, hence the stunting of the iris.  The iris might also
have been hurt by the herbicide, or a combination of both might happen.

By the way, many of the sites I found were about using other highly
competetive plants to suppress CT.  Alfalfa was especially effective, it
seemed.  Many of the sites expressed concern about CT rapidly developing
resistance to most of the common weedkillers.  Evidently 2, 4D is already
ineffective against many populations.  Biological control measures include
at least one insect and a fungus disease.  CT weakened by the insect and the
fungus becomes more susceptable to herbicides.

Also recommended was strict removal of any and all shoots as soon as they
appear, and the avoidance of cultivation.  Cultivation cuts up the roots and
each tiny piece produces a new plant.  However, if all shoots are removed as
soon as they appear, control can be achieved in two years.

Then new seedlings come in.

Luckily CT does not thrive where summer temperatures regularly go above 90F.
We do not have it here in Piedmont VA, so far as I know, though there are
other thistles both alien and native.  In the west it is a range pest in
cooler, moister regions.

Bill S.


------------------------ Yahoo! Groups Sponsor ---------------------~-->
FREE COLLEGE MONEY
CLICK HERE to search
600,000 scholarships!
http://us.click.yahoo.com/Pv4pGD/4m7CAA/ySSFAA/2gGylB/TM
---------------------------------------------------------------------~->

 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index