From: dr@ducvax.auburn.edu
Newsgroups: misc.rural
Subject: Re: Thistles
Date: 14 Oct 92 23:39:03 GMT
Distribution: usa
Organization: Auburn University, AL

In article <10320@tetons.idaho.amdahl.com>, gnd@idaho.amdahl.com (Greg Darnell) writes:
> 
>    <some deletions>           ...  In my experience with bull thistles
> and Canada thistles, mowing simply causes them to grow shorter and thicker,
> crowding out any grass near them.  In an area that is almost entirely 
> thistles, mowing turns it to solid thistle leaves, and residual seeds from
> earlier years will come up the next year.  I have seen other varieties die
> from mowing, so it depends on what type you have.  The above two types only
> die by spraying or digging.

Don't know which Bull Thistle you mean, but both of the thistles with
that common name (Carduus lanceolatus and C. pumilus) are listed in my 
favorite reference manual, R.A.B. [1] as biennials; if this is correct, 
mowing should work as an eradication method, altho not necessarily by
the first year.

Of the 15 thistles listed in R.A.B., 13 are biennials.  C. repandus
is listed as "Biennial or possibly perennial", while Canada Thistle 
(C. arvensis) is listed as a "Perennial from rhizomes, forming colonies...".

>                                                       ...  It's nice to
> avoid chemicals if you can, but it would be naive to believe that will
> eliminate your (or your horses) exposure to them.  The alfalfa and oats
> grown around me are often sprayed with herbicides or pesticides as well
> as the potatoes, so it seems to me that unless you control the production
> of everything you consume you'll end up with exposures anyway. 

Even if eliminating exposure is infeasible, surely we all agree that 
*reducing* exposure is generally beneficial, in multiple ways?

>  Personally I dig the few thistles that show up in our mature pasture.

I *have* to ask:  Do you mean you dig them up, or do you mean that 
you find them aesthetically interesting? ;-)

> In our new pasture, which came up heavily infested with some unknown
> broadleaf weed, I sprayed it after the grass was old enough to handle it
> and stopped the problem early.  
> -- 
>  Greg Darnell    Amdahl Corporation    143 N. 2 E., Rexburg, Idaho 83440
>   UUCP:{ames,decwrl,sun,uunet}!amdahl!tetons!gnd          (208) 356-8915
>   INTERNET: gnd@idaho.amdahl.com

The take-home lesson, I think, is that one should look at the the ecology
of the system one is working with.  Mowing after seed set is unlikely to
do much to eliminate the local population; indiscriminate and poorly timed
spraying can be even more deleterious.

	D.R.

[1] \Manual of the Vascular Flora of the Carolinas/ by Radford, Ahles, and Bell
   University of North Carolina Press,  ISBN 0-8078-1087-8

I highly recommend this book for anyone interested in identifying flora east 
of the Mississippi river (not too shabby for west of Mississippi either). 
Similar in usefulness, cost, weight, # pages to a good desktop dictionary.

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