I knew herbicides could damage grass if they were applied in the wrong place. What I hadn’t thought much about was what could happen after the application—when rain or irrigation carries them downhill toward grass that wasn’t supposed to be treated.
That caught my attention while reading a study published in Weed Technology. When different grasses are growing close together on a golf course, something that works well in one area could cause trouble just a few feet away.
Researchers looked at two herbicides, tetflupyrolimet and pronamide, to see how far their effects could reach downhill. Tetflupyrolimet is being studied as a possible future option for turfgrass weed control. Pronamide was included because researchers already knew it could move downhill.
The trials took place at NC State University in 2023 and 2024. Researchers used a sloped area with sandy loam soil and tested the herbicides under two different soil-moisture conditions.
They planted perennial ryegrass to help track the effects. If the ryegrass died below the treated area, that gave them evidence that enough herbicide had reached it to cause damage. They checked the grass over eight weeks following treatment.
| Herbicide | Farthest observed injury downhill |
|---|---|
| Tetflupyrolimet | About 3.6 feet |
| Pronamide | About 5–6 feet |
Researchers measured perennial ryegrass injury downhill from treated areas. These distances reflect the study’s conditions and are not recommended buffer distances.
Source: Pritchard and colleagues, Weed Technology, 2025. Read the study.
Here’s the part that stood out to me: damage associated with tetflupyrolimet reached about 3.6 feet downhill. With pronamide, the farthest damage was roughly five to six feet, depending on the conditions.
That may not sound like much until you picture two types of grass growing right next to each other. There doesn’t have to be much distance between the area being treated and something you want to protect.
The researchers suggested that leaving about 3.6 feet between a tetflupyrolimet application and sensitive grass might provide protection under conditions like those in the study. But that number comes with some limits.
This was one location, with one soil type and one slope. The researchers also removed the aboveground bermudagrass canopy and planted ryegrass specifically for the experiment. A golf course with different soil, ground cover or water flow could respond differently.
They were measuring dead ryegrass, too. That tells us where damage showed up. It doesn’t prove that no herbicide traveled farther.
For me, this was a reminder of how much goes into taking care of a golf course that golfers may never see. Choosing a treatment is one decision. Thinking about the next rain, where the water will go and what’s growing downhill adds another layer.
The paper discusses tetflupyrolimet’s possible future use in turfgrass. Any application would need to follow the current approved product label. The distances in this experiment shouldn’t be treated as directions for using a product.
FMC funded the study, and one of the authors worked for the company, as disclosed in the paper.
I came away with a better appreciation for why superintendents have to look beyond the patch of weeds they’re trying to control. What’s growing a few feet away matters, too.
Source: “Downslope lateral movement of tetflupyrolimet and pronamide in turfgrass,” Pritchard and colleagues, Weed Technology, 2025. Read the study.
