mares tail

It's survived since prehistoric times ... 

The advice is to try to pull it up as often as you can.  Try to remove it before the spores are shed.  If you choose to apply weedkiller, bruise the leaves first otherwise it's pointless because the silicone coating prevents absorption.

Never let it see a Sunday, and you will eventually weaken it.

As well as pulling it up as often as possible, try to improve the soil condition, mares tail likes poor soil so good soil quality discourages it.

I have it on both my plots, worse on one. As others have said just keep hoeing it/digging it out whenever you see it.

From my research it seems to like low oxygen and acidic conditions. Hence it rather likes my acidic heavy clay soil. I think improving the conditions will help a lot. I've been adding calcified seaweed and green manures to my beds as well as digging/hoeing the roots whenever I'm at the plot and it does seem to have helped. This is my second year and it doesn't seem as bad as last year.

Also it doesn't seem to like competition. Where I grew potatoes the horsetail was much less prevalent which I assume is from the dense canopy of foliage that the potatoes produce.

Very interesting,thanks for posting.