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Horses in pasture

Listed are some frequently asked questions related to Prowl H2O for weed control in perennial warm-season grass pastures and hayfields.

I thought Prowl H2O was only labeled for use in bermudagrass. Has this changed?

Yes. A new supplemental label now includes additional perennial warm-season grasses such as bahiagrass, switchgrass and others.

What about cool season grasses like tall fescue?

No. Prowl H2O is NOT labeled for use on tall fescue or other cool season hay and pasture grasses.

What is the recommended timing?

For summer annual weed control, apply in late winter when perennial warm-season grasses are still dormant. Prowl H2O is not labeled for use after green up. It can also be applied earlier in the winter after the onset of perennial warm-season grass dormancy for winter annual weed control. However, it will not control weeds that have already germinated in the fall prior to perennial warm-season grass dormancy.

What is the recommended rate?

2-4 quarts per acre. Note: the label goes lower than 2 quarts/A, but producers will not be happy, as the length of weed control will be limited. Therefore, for summer annual weed control, it is not recommend using less than 2 qt/A. The annual grass weed control is good at 2 qt/A and is excellent at 3 qt/A.

Can I use Prowl H2O on newly planted warm-season forage grasses?

N0, it is only labeled for established warm-season forage grasses (grasses that have gone through at least one mowing or cutting).

Do I need to add a surfactant to make Prowl H2O work better?

No, this herbicide only has pre-emergent activity. Any weeds that have already emerged will not be controlled. If you are tank mixing Prowl H2O with a post-emergence herbicide, then a surfactant may be needed.

What makes this treatment stand out?

With a late winter application, residual control of many grass weeds can be achieved into August at the 3 quart or higher rate. Note: hurricane type rainfall events over the summer will likely result in weed control breaking sooner than expected.

What will frustrate producers with Prowl H2O treatment?

Two main things:

  1. If it is applied in late winter without a post emergent tank mix partner (like glyphosate), the winter annual weeds will keep growing and the weed control will not be observed until after first cutting (early apparent failure)
  2. It will not control established perennial weedy grasses such as dallisgrass, vaseygrass, rhizome Johnsongrass, or knotroot foxtail. They may even be released and get worse. This is where weed ID is critical.

Are there any other label restrictions I should know about?

Yes, there is a 45 day grazing/forage harvest and 60 day hay cutting restriction. This means producers need to time the dormant season application at least 60 days in advance of first cutting.

What weeds are controlled?

At 2 quarts/A, Prowl H2O will control:

  • barnyardgrass
  • crabgrass spp.
  • crowfootgrass
  • seedling Johnsongrass
  • annual foxtails
  • Texas and fall panicums
  • goosegrass
  • field sandbur

Above 2 qt/A, there are additional species on the main Prowl H2O label.


Reviewed by Dr. Leanne Dillard, May 2019.

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