On Sun, 12 Aug 2012 14:06:54 +0100, Janet Tweedy
wrote:

Which weedkiller would be your choice on a cracked driveway (concrete0
next to a house? Have been asked to recommend on to kill off elder and
dandelions that are growing up through the cracks in the concrete. It's
a rented property for 6 months.
Should they go for the slow acting but possibly more effective
gylsophate or the path clearing stuff which acts quickly but may not
control the roots.

Glyphosate will only kill existing weeds. It will not prevent growth
of new weeds. Something like Pathclear will kill the existing stuff
(also slowly) but also has a residual action that will help to prevent
new weeds for about 3 months.

The slow-acting weedkillers are slow because they work down and kill
the roots. If top growth is killed too quickly, the roots won't be
killed properly and will regrow.

What a lot of people forget, though, is if using anything residual
like Pathclear you need to wet the ground as well as the plants! If
the cracks are very narrow, it may not be possible to get anything
into the cracks effectively.

With either type of herbicide, they will probably need a repeat
treatment to successfully kill off elder and dandelions.

Cheers, Jake
=======================================
Urgling from the East End of Swansea Bay where sometimes
it's raining and sometimes it's not.