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Horsetail (Equisetum) Control (06/09/16)

Two Questions on Horsetail are discussed.

Horsetail (Equisetum) Control

Question #1: I have a customer who has been seeing more and more horsetail in both corn and dry beans. I know horsetail can be mis-named as marestail but horsetail is the weed that is similar to smooth scouring rush. Is there anything we can do for control of this weed species?

Question #2: My home garden and property has been taken over by horsetail. I achieved top kill with a spray of 20% acetic acid (vinegar) plus a small amount of dishwashing liquid. I then added glyphosate in hopes of root kill, not just top kill. I've seen inconsistent statements online about whether glyphosate alone works on horsetail but thought this mix might work, although a search for horsetail remedies in general, and agricultural vinegar specifically, did not turn up anyone else trying this combination.

It is too early to know the results in my own garden. Before I put in more time, money and effort I wanted to ask: Do you think it likely this might have the desired effect? Is there a different strategy, mix or product(s) you'd recommend?

Another strategy I've read about, reapplying the acetic acid/dish detergent mix repeatedly without glyphosate, to try to weaken the roots eventually, is not tenable during the growing season so only achieving top kill won't solve the problem. And the horsetail may be too widespread throughout the property for repeated applications to be reasonable.

Answer: First some background: Horsetail is a perennial, is prehistoric as it reproduces by spores and expansion of underground roots, has no leaves to intercept spray droplets which is the primary plant organ for herbicide absorption, and has a thick waxy cuticle that repulses spray droplets making droplet retention difficult.

Acetic acid is similar to any other acid like sulfuric, citric and others. Acids burn – that is their mode of action. Acid burn just desiccates top growth which is quickly replaced by new top growth of perennial plants. The acid does not translocate down to roots and does not kill underground roots. Theoretically, one can continue to burn off top growth and starve the roots, but that would take years and require fastidious attention to timely and repeated applications.

Glyphosate is one of the most water soluble herbicides used. In other words, absorption of a hydrophilic (water soluble) soluble herbicide across a lipophilic (oil soluble) barrier (waxy cuticle) is difficult. Average absorption of glyphosate in most weed species is 3 to 49% with an average of 33%. Your dishwashing liquid replaced surfactants that growers normally use to help stick droplets to plant foliage and increase absorption. The dishwashing liquid only enhanced acid burn and did nothing to increase translocation to kill underground roots.

Adding glyphosate with an acid to increase horsetail control is futile and counterproductive as the quick burn from the acid prevents translocation of the highly phloem mobile glyphosate herbicide down to perennial roots. The above information in not encouraging for your success in killing this weed. To be successful you must not only prevent the underground roots from spreading but kill roots even if over an extended period of time.

                Options:

  • Option 1: Use a long spade (>12 inches) and dig deep to expose underground roots. Remove roots after turning soil. Even if you have to do it section by section, this may be the most efficient control practice.
  • Option 2: Below is the section in our ND Weed Control Guide (page 69) showing chemical control of horsetail.

zollinger.2.table

The table shows other herbicides that are much more effective than glyphosate to control horsetail but they will require multiple application to reduce the root mass. Most herbicides will leave a residue in the soil and will prevent planting garden and flower species. Do not use Glean as it will persist for several years. Permit/Sedgehammer and Python are corn herbicides and will not allow planting garden/flower species for 2 to 4 years after application. Remedy and MCPA will leave a residue for I month and will be more effective than glyphosate. It may require repeated applications of Remedy (triclopyr) and MCPA which may take that portion of your garden out of production until the roots are killed.

  • Option 3. This option has NO scientific foundation and is just speculation from me. Mix a 50:50 solution of glyphosate + water. Using a hypodermic needle inject the solution into the hollow stems of the horsetail. This should really not take that long of time. This bypasses limited herbicide entry into horsetail from normal absorption processes. Glyphosate symptoms and phytotoxicity usually takes 7 to 10 days to be expressed and full control will not be realized until 14 to 21 days. Try this on many stems and see what happens. Glyphosate leaves no residue in the soil but leaves one important point to consider……researchers have seen a phenomenon called root exudation from some plants after receiving an application of glyphosate – some plants exude the glyphosate through the roots and other plant roots in close proximity can absorb the exuded glyphosate and those nearby plants will die. In other words, if horsetail exudes glyphosate through underground roots the garden/flower plants in close proximity to the horsetail stems may also be killed.

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Rich Zollinger

Extension Weed Specialist

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