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 – 4.2 quarts per acre however, a split application of 2.1 quarts and 2.1 quarts later how 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.
Prowl H2O is a dinitroaniline 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 (mycrostegium), chickweed, mustards, and knotweed.
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.
In a study conducted at Penn State University and the University of Delaware comparing Prowl H2O applied at 1, 2.1, or 4.2 qt/A PRE to weeds and 2.1 qt/A PRE to weeds and after first cutting (May 31).
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 but in controlling giant foxtail, they concluded that Prowl H2 O at 2.1 quart per acre maximized PRE giant foxtail control. Giant foxtail is an annual foxtail similar to yellow and green foxtail which are prevalent in Alabama. We have a perennial foxtail called knotroot foxtail that we are looking at Prowl H2O and other herbicides to determine the best option for control.
Reviewed by Dr. Leanne Dillard, May 2019.
Graph and data used with permission from Mark VanGessel, University of Delaware