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Perennial Weed Control in Grass Hay and Pasture

At the recent Ag Progress Days in Pennsylvania one of the most common questions asked involved perennial weed control in grass hay and pasture. While we still have nice warm days, it is good time to scout pasture and hay fields for the presence of perennial weeds. As you hopefully have heard before, late summer and fall is the best time to control most perennials with a systemic herbicide because herbicides are moved into the root systems allowing more permanent control. With the autumn weather, these plants more actively transport carbohydrates and sugars to underground storage structures such as rhizomes, tubers, and roots to enable them to survive the winter and to provide the necessary energy to begin the next cycle of growth in the spring. Mowing the pasture and hay fields in mid-summer or several weeks before the herbicide application to prevent seed production and to promote healthy new leaf tissue that can intercept the herbicide is also important. In general, the application window runs from early September through October depending on where you are in the state and what weeds you are targeting. For the warmer season perennials like johnsongrass, horsenettle, groundcherry, wirestem muhly, Japanese knotweed and poison ivy, herbicide application between September 1 and 15 is generally ideal. For weeds like hemp dogbane and bindweed, make applications before October 1, and for quackgrass, other cool season grasses, and Canada thistle, try to make applications by October 15. These suggested dates target central PA, so adjust by a week or so forward or backward if you are south or north. Here is a list of the most common herbicides labeled for grass pasture and hay and some of their strengths/precautions.

  • 2,4-D is marketed by various companies with various trade names. Rates generally range from 1 to 2 quarts per acre. Refer to the label provided with the product for specific recommendations and restrictions as formulations vary. 2,4-D provides postemergence control several annual, biennial, and perennial broadleaf weeds. Ester formulations are slightly more effective (more leaf-absorbed) than amine formulations, but also slightly more volatile so greater care must be taken when making applications next to sensitive species such as grapes. Interval between application and grazing is 0 to 7 days depending on type of animal and is 30 days for haying. 2,4-D is often tank-mixed with dicamba as a general broadspectrum broadleaf herbicide.
  • Dicamba – Banvel (DMA), Clarity (DGA), Engenia (BAPMA), Fexapan (DGA + VG Tech), and Xtendimax (DGA+VG Tech) provide postemergence control and less than 1 month of soil residual control of a relatively broad spectrum of annual, biennial, and perennial broadleaf weeds. Rates vary by formulation but generally can be applied at up to 1 lb ae per acre to established grasses. Interval between application and grazing ranges from 0 to 40 days and 0 to 70 days for haying depending on rate of application and type of animal. Dicamba is often tank-mixed with 2,4-D as a general broadspectrum broadleaf herbicide.
  • Crossbow – contains a mixture of 2,4-D ester and triclopyr ester. Generally applied at 1 to 3 quarts per acre. Commonly used for brush control and effective for control of a number of problem weeds including smooth bedstraw. Grazing restrictions range from 0 days up to the next season (for lactating dairy) depending on animal type and 14 days for haying.
  • GrazonNext HL – contains aminopyralid + 2,4-D amine. This product was formerly marketed as ForeFront HL in our region and Milestone herbicide contains the single active ingredient aminopyralid. GrazonNext provides postemergence control and 2 to 3 months of soil residual control of many annual, biennial, and perennial weed species in permanent grass pasture. GrazonNext is particularly effective on thistles, horsenettle, and smooth bedstraw. The GrazonNext label has restrictions concerning the use and management of plant residues (hay, straw, mulch, compost) and manure that may contain aminopyralid residues. These include important restrictions concerning the movement and sale of hay products treated with aminopyralid. Be certain you understand and are able to follow these label restrictions before using this product. Interval for application and grazing is 0 days and 7 days for haying.
  • Metsulfuron 60DF – Metsulfuron provides both postemergence control and 2 to 3 months of soil residual control of many annual, biennial, and perennial weed species, and suppression of blackberry and multiflora rose in permanent grass pasture. Metsulfuron is also effective on seedling spiny amaranth. Special precautions are provided on the label for applications to fescue or timothy. Do not use metsulfuron on Italian (annual) or perennial ryegrass, or severe injury will occur. Cimarron Max is a co-pack that contains the active ingredients of metsulfuron and 2,4-D plus dicamba. Cimarron Plus is a premix with the active ingredients metsulfuron and chlorsulfuron (Glean or Telar). Interval for application and grazing and haying is 0 days, however allow time for the herbicide to work before harvesting for hay.
  • Overdrive 70WDG – contains dicamba (Na-Salt) + diflufenzopyr. Overdrive is applied at up to 8oz per acre and provides postemergence control and less than 1 month of soil residual control of several annual, biennial, and perennial broadleaf weeds. Interval for application and grazing and haying is 0 days, however allow time for the herbicide to work before harvesting for hay.
  • PastureGard contains triclopyr ester + fluroxypyr and provides postemergence control and 1 to 2 months of soil residual control of many annual, biennial, and perennial weeds as well as many woody plants. Interval for application and grazing and haying is 0 days, however allow time for the herbicide to work before harvesting for hay.
  • Remedy Ultra 4L contains triclopyr ester and provides postemergence control and 1 to 2 months of soil residual control of many annual, biennial, and perennial weeds as well as many woody plants. Interval for application and grazing and haying is 0 days, however allow time for the herbicide to work before harvesting for hay.
  • Stinger 3S contains clopyralid and provides postemergence control and 1 to 3 months of soil residual control of some annual, biennial, and perennial broadleaf weeds, but it is primarily used for Canada thistle control. Interval for application and grazing and haying is 0 days, however allow time for the herbicide to work before harvesting for hay.
  • Weedmaster 3.87L contains dicamba DMA + 2,4-D amine and provides postemergence control and less than 1 month of soil residual control of many annual, biennial, and perennial broadleaf weeds. Interval between application and grazing ranges from 0 to 7 days depending on type of animal and 37 days for haying.
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