Suppressing Tall Whitetop: It’s Hard Work, But Possible

Rangeland overtaken by the weed known as tall whitetop, or perennial pepperweed, can be restored to grassland, as Agricultural Research Service scientists in Reno, Nev., have shown for the first time.

The weed has become a nemesis of ranchers and land managers across the West and in New England. The plant can grow eight feet tall in wet areas along streams, rivers, ditches, irrigation canals and salty marshes.

Researchers in the ARS Exotic and Invasive Weeds Research Unit have explored a variety of pesticides--as well as grazing and seeding strategies--to subdue the weed and have found an approach that works.

First, spray the area with 2,4-D. Unlike many other pesticides the scientists tested, 2,4-D doesn’t leave a residue in the soil that would prohibit using the land for growing crops like alfalfa.

Second, plant either tall wheatgrass or robust needlegrass, a competitive species under evaluation by ARS researchers in Logan, Utah. Both of these perennial grasses can outcompete tall whitetop if managed properly. The needlegrass may be desirable because it is also a native plant. And unlike a related plant known as “sleepygrass,” robust needlegrass does not contain toxins harmful to animals.

A second year of limited 2,4-D application is necessary to help get grasses established. Land managers may have to graze the area to minimize stubble accumulation during the winter. That’s because large amounts of stubble give voles and rabbits lots of places to hide from the hawks that normally prey on them. Large rodent populations will eat the grass seed, allowing tall whitetop to reinfest.

More: Goats chew tall whitetop down to size (1998)

The key, according to scientists, is management. Spraying pesticides alone won’t stop tall whitetop, even if it’s done annually. Goat grazing also won’t work by itself, nor will planting grass seed without following up.

ARS is the chief research agency of the U.S. Department of Agriculture.

Scientific contact: James A. Young, ARS Exotic and Invasive Weeds Research Unit, Reno, Nev., phone (775) 784-6057, fax (775) 784-1712, [email protected]; or Tom Jones, ARS Forage and Range Research Unit, Logan, Utah, phone (435) 797-3082, fax (435) 797-3075, [email protected].