Dwight Lingenfelter, Extension Associate, Weed Science and William S. Curran, Ph.D., Emeritus Professor of Weed Science, Pennsylvania State University

Continuously grazed pasture allows for selective grazing, reducing desirable forage competitiveness against weeds and leading to weed encroachment and spread.

Now is the time to scout grass pastures and hay in search of winter annual and biennial weeds. Both of these types of weeds are potentially susceptible to control right now and an effective herbicide application will prevent flowering and seed production.

Management of perennial weeds such as dandelion, Canada thistle and the woody perennials such as multiflora rose and autumn olive is best performed a bit later in early summer after plants reach the bud-to-bloom stage. Winter annuals including the mustard species, common chickweed, horseweed/marestail, deadnettle/henbit, fleabane, etc. are growing rapidly and have already or will begin to flower and set seed very soon. Biennials including musk and plumless thistle, burdock, wild carrot, etc. should be treated before they begin to bolt and the smaller the better. (Late fall or early spring is really the best time to treat them). The most common herbicides used for control of many broadleaf weeds in grass hay/pasture this time of year are the plant growth regulator herbicides such as 2,4-D, dicamba (Banvel, Clarity, etc.), triclopyr products (Crossbow, Garlon, etc.), and clopyralid (Stinger, PastureGard, etc.). In addition products containing metsulfuron (Cimarron, other generic formulations, etc.) can provide good control of many broadleaf weeds in the spring. (Be cautious, if forage grasses were recently seeded and are not yet established many of these herbicides can cause severe crop injury.)

Secondly, many of you know that Prowl H2O now has a supplemental label for use in cool and warm season forage grasses to control certain annual grasses and broadleaf weeds. This has been a much anticipated label since it allows for better control of weedy annual grasses such as crabgrass, foxtails, panicum, Japanese stiltgrass, etc. and others in grass forage settings.

Prowl H2O may be applied to established perennial forage grasses (including Kentucky bluegrass, bromegrass, tall fescue, orchardgrass, perennial ryegrass, timothy, switchgrass, and others) grown for forage, green chop, silage, hay production, and/or grown in pastures for livestock grazing.

  • Apply at a broadcast rate of 1.1 to 4.2 quarts of Prowl H2O per acre in a single application or sequential applications made 30 or more days apart. Herbicide must be applied before weed germination in spring, or in-season between cuttings, otherwise weeds will not be controlled. Prowl H2O maybe tank-mixed with other labeled herbicides, but keep in mind nothing is labeled for control of emerged grasses in grass forage.
  • Split applications of Prowl H2O are better than a single, high-rate early season application. Make the first application in early spring (mid-March to early April) but before weed germination (2-3 pt/A); and then the second application right after first (or second) cutting (3-4 pt/A)
  • Prowl H2O may be applied to mixed stands of established cool-season forage grasses and alfalfa (established alfalfa is defined as alfalfa planted in fall or spring which has gone through a first cutting/mowing). Do not apply Prowl H2O to mixed stands of cool-season forage grasses with other forage legumes besides alfalfa.
  • There is no preharvest or pre-grazing interval for Prowl H2O-treated grass forage, green chop, silage, hay, or pasture.
  • Mixed stand alfalfa/cool-season forage grasses may be grazed or harvested for forage or hay 14 or more days after applying Prowl H2O.