Prowl Registration for Cool-Season Grasses

Mark VanGessel, Extension Weed Specialist; and Quintin Johnson, Research Associate, Weed Science;

Prowl H2O received a supplemental label for use in cool and warm season forage grasses. Prowl H2O can provide residual control of a number of annual grass and small-seeded broadleaf weeds. Prowl H2O will not control weeds that have emerged.

A number of comments from the supplement label for cool-season grasses include:

  • May be applied to solid stands of perennial forage grasses (including bentgrass, 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 only to established (grass with 6 or more tillers per plant) perennial cool-season grasses.
  • 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 fall after the last cutting/mowing/grazing, in winter, in spring, or in-season between cuttings, otherwise weeds will not be controlled. Prowl H2O maybe tank-mixed with other labeled herbicides.
  • Do not apply more than a total of 4.2 qts of Prowl H2O per acre per year.
  • 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.

The pre-harvest interval (PHI) for warm season grasses has been reduced from 60 days to no pre-harvest interval.

Be aware that the replant interval for alfalfa is 6 months and at least 10 months to replant annual or perennial grass crops. So be aware how long you intend to keep your stand and/or if you intend to over-seed your stand.

Prowl H2O is the only formulation of pendimethalin labeled for these uses.