The weed referred to as ‘Marestail’ is actually the common horsetail plant (Equisetum arvense).

It is an invasive and deep rooted plant that grows via fast-growing rhizomes (underground stems). Horsetail is a very primitive plant that was around before the dinosaurs. It reproduces by producing spores that are airborne and travel on the wind. If the underground stems are chopped up the plant will also spread.

It has separate non-reproductive and fertile spore-bearing stems. The fertile stems are produced in early spring and are usually brown in colour. These initial stems die back and the non-reproductive green stems start to grow throughout spring, summer and until the first autumn frosts. On an allotment, this plant tends to appear where little competition exists. It can be especially annoying when you take the time to clear your plot of other perennial weeds for marestail to show up in abundance. Under Granville Park there is a water course and the weed follows this in a ‘band’ across the ground.

What can I do about it?
Control of horsetail is challenging! Repeated removal of the green sterile stems will deplete the plant’s energy reserves. Eventually this will exhaust the rhizome but this can take many years. Removing and disposal, for example by burning, of the reproductive stems in early spring will help stop the weed spreading. Also, under no circumstances, rotovate the ground where there is evidence of this plant. If you do this, every tiny bit created will produce a new plant and you will increase the infestation drastically.

Dig out the green stems throughout the growing season – repeatedly! It will take years and dedication. The positive side is that, although marestail is annoying, you can still grow crops. It doesn’t smother plants like vine-growing weeds like bindweed. Most plots have this weed – you just have to learn to live with it and try and keep it in check. Ensure you remove as much of the underground structure as you can. This can go very deep (like 7ft!) so it isn’t always possible to get it all out, but try and follow the black rhizomes and get them out as thoroughly as you can.
Covering to exclude light will control the top growth, but you will still need to deal with the rhizomes once the area is uncovered.

The weedkiller glyphosphate, the active ingredient in Roundup, will kill marestail if you can create the right conditions for the plant to absorb the chemical. Due to the small surface area of the stem and the waxy cuticle on the outside of its leaves, the plant is well adapted to prevent it’s uptake. If you bruise the leaf by rolling it before application this can help. Other ideas include using a weed burner to slightly damage the leaves before application or mixing the weedkiller with wallpaper paste and using this more viscous solution to help penetration.
The weedkiller Kurtail, which is based on the chemical glufosinate-ammonium, is claimed to be very effective against marestail. This chemical is licensed for professional use only, although it seems to be freely available on ebay!

In summary

  • Dig out the rhizosomes and try to keep these as intact as you can every bit you break off will grow a new plant.
  • Try chemical control if you are happy to do so.
  • Do not rotovate as this will make the problem far worse.
  • Keep digging the weed out around your crops throughout the growing season (repeatedly).
  • Learn to live with it, whilst in the knowledge that it will reduce overtime with continued cultivation.