On Wed, 14 Aug 2013 21:41:37 +0100, Rick Hughes wrote:

Been trying to kill off Mares Tail with Glyphosphate ........ almost
zero impact

Mares Tail is one of the tough buggers, mainly beacuse the outer skin
of the plant pretty water proof so the glyphosate has trouble getting
into the plant in suffcient quantity. Give the plants a gentle
bruising (walk on them) before spraying.

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Cheers
Dave.