In the past, Prowl H₂O was only labeled on dormant bermudagrass. It now can be used on cool-season forage grasses with or without alfalfa (not clovers). It is labeled for grasses grown for forage, green chop, silage, hay production, and/or grown in pastures for livestock grazing. It is also labeled in warm-season grasses however, both warm and cool-season grasses must be established (6 or more tillers). The rate is 1.1 to 4.2 quarts per acre, however, a split application of 2.1 quarts has shown to be effective. It may be tank-mixed with other forage herbicides. Refer to the label for tank-mix partners. Prowl H₂O may be applied in the fall, spring, or in-season between cuttings.

Researchers at Penn State and the University of Delaware compared single (early spring) applications of Prowl H2O to a split application applied prior to crabgrass emergence. Graph and data used with permission by Mark VanGessel, University of Delaware.

Prowl H₂O is a herbicide that controls grasses and small-seeded broadleaf weeds. It will not control emerged weeds. It’s strengths at less than 4 pints include crabgrass, foxtail, panicum, pigweed, smartweed, henbit among others. At 4 pints or greater per acre, it will control annual bluegrass, ryegrass, brome, Japanese stiltgrass, chickweed, mustards, and knotweed. Prowl H₂O must be rainfall incorporated into the soil for herbicide activation. At least 0.25 inch of rainfall within 7 days following application is preferred for desirable activity.

There are no grazing restrictions with Prowl H₂O. Plant back restrictions to grasses are 10 months so, overseeding immediately is not an option.

Prowl H₂O may be applied by ground or chemigation, by air, or on dry fertilizer. The minimum application interval is 30 days. The maximum cumulative total allowed per year is 4.2 quarts per acre. Solid stand minimum pre-graze or pre-harvest interval is 0 days. In a mixed stand, a 14-day pre-graze or pre-harvest interval exists.

Shown in the graph, the length of residual crabgrass control increases with the Prowl H₂O rate. The 4.2 quart per A rate provided about 12 weeks control but not full-season. However, the split-application of 2.1 quart followed by 2.1 quart did provide season-long control and was the only treatment to do so.

In another study conducted at Virginia Polytechnic Institute, evaluating the same rates on giant foxtail, they concluded that Prowl H₂ O at 2.1 quart per acre maximized giant foxtail control.