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What Herbicides Work Best to Kill Monkey Grass?

Monkey grass belongs to the genus Equisetum and is also referred to as "horsetails" and "scouringrush." The various species of grasses in the group differ on account of stem thickness, height and vegetative growth. The grass does not produce flowers or seeds but spreads with spores that easily make their way where they are least desired, such as agricultural fields. Monkey grass is a common problem in ditches and around ponds. A number of herbicides work well to control the growth of monkey grass.
  1. Clopyralid

    • Clopyralid is cited by the Purdue University Extension website as being among the best herbicides for the control of monkey grass. Clopyralid is used for the effective control of a number of broadleaf weeds in lawns, including clover, dandelions and thistle. The herbicide is also commonly used in agricultural crops, including cereal grains and is sold under different tradenames. Clopyralid is a synthetic form of the naturally occurring plant hormones known as "auxins." The herbicide causes abnormal growth of targeted weeds, leading to stunted growth and eventual death.


    • MCPA is listed by Purdue University's Extension site as an effective herbicide for the control of monkey grass. The herbicide is a systemic, post-emergent herbicide that controls perennial and annual weeds, including thistle and docks. MCPA is commonly used for the control of weeds like monkey grass in a variety of crops, including potatoes, rice, peas and cereals. MCPA is often used in combination with other herbicides for improved performance. MCPA is combined with clopyralid for use on monkey grass. MCPA has a slightly higher level of toxicity and can potentially cause severe eye irritation.


    • Purdue University Extension cites the use of herbicides with the active ingredient glyphosate as good choices for curtailing the growth of monkey grass. Glyphosate is a general-use herbicide sold under different trade names and is effective for the control of grasses, herbaceous plants, deep-rooted weeds, and even some broadleaved trees, conifers and shrubs. The herbicide is not entirely effective on all woody plants and timing is a critical consideration for the herbicide to be effective on a number of plants. Glyphosate is applied directly to foliage, where it is absorbed and then dispersed throughout the plant. The chemical hinders the production of amino acids in the weeds, leading to the eventual death of the plants.