I have a rather large perennial garden fairly close to a purple loosestrife
marsh, and constantly have to battle the loosestrife to keep it out of my
garden.  (I have almost totally given up on the marsh.)  When I first started
the garden, I threw out all the tall weeds I could easily uproot, then
rototilled the weedy ground well before planting.  I can attest that the
loosestrife grew back from every small piece of rootstock that was broken up
by the tiller.  It was a mess!  Also, seedlings keep coming up that have
blown in from the marsh.  These seeds are extremely tiny and easily blown by
the wind.

One good thing I have learned, however.  Loosestrife will not grow in dense
shade, and a barrier of dense shrubs and trees will slow its spread.  I am
contemplating planting various swamp trees in my marsh to hopefully kill it
there by shade.  Obviously this is a long term project, and the trees will
have to be well protected or they will be killed off before being large
enough to have any effect.  I have no confidence that the Galerucella beetles
will make much of a dent in the huge stands of purple loosestrife that we now
have.

Ted Fischer
Dexter, Michigan USA