Puncturevine is nasty weed

KENNEWICK -- You don't have to be a gardener to utter nasty epithets about puncturevine, also known as tackweed or goathead in our region.

Puncturevine is a summer annual that grows prostrate along the ground with vines that can reach eight feet in length. It thrives in open ground on dry, loose sandy soils, but it's also found in compacted, heavier soils.

Many of us find it in gravel driveways and parking lots, along bike paths, on roadside shoulders, rights-of-way, playgrounds and more.

Puncturevine appears innocuous with its pretty little yellow flowers and delicately divided leaves, but anyone who has stepped on one of its burs or had a bike tire punctured by a bur knows the pure nastiness of this ground-hugging weed.

Once puncturevine starts blooming in spring, it will keep flowering and producing seeds through to October. Each flower produces a woody fruit containing five spiny burs or segments, each of which contains from 1 to 4 seeds. While not considered extremely prolific compared to other weeds, it's been estimated by weed scientists that one plant growing without competition can produce over a million seeds. (Imagine if it was considered prolific!)

While it takes over six months for the current season's seeds to mature, seeds already in the soil will continue to germinate all summer and into early fall. Mature seeds can persist in the soil and remain viable for three years or more. Where puncturevine is a persistent problem, monthly pulling or cultivation with a hoe is an effective non-chemical means of control... if kept up for four years or more.

Believe it or not, puncturevine plants are fairly easy to control. Shallow cultivation with a hoe will destroy them.

If burs have already formed, plants should be removed and thrown away. Puncturevine is also easily controlled with chemical herbicides, including 2,4-D in lawn situations, glyphosate and diquat on bare ground, and glyphosate, glufosinate and diquat in landscape beds.

Even though the chemicals provide good control of current puncturevine plants, they aren't effective on the new plants that will continue to germinate. Retreatment is necessary for each new "crop" of plants. Oryzalin (Surflan) is a pre-emergent herbicide that can be used effectively in landscape beds to prevent puncturevine germination for the entire season, but treating large areas of land would be costly.

As a gardener, the first line of defense in weed control should always be prevention. Puncture vine takes advantage of open ground areas, but it's not very competitive. It can be discouraged by planting grass or using a mulch, such as a three inch layer of bark or a synthetic fabric mulch.

Speaking of puncturevine or "tackweed," do you know about The Great American Tackweed Pull Day on June 25? Because of changing restriction regarding the use of herbicides close to the river, the city of Pasco and the Franklin County Noxious Weed Control Board have teamed up to sponsor the "Pull" event. Their goal is to get volunteers to pull all of the tackweed growing along the Sacagawea Heritage Trail.

Volunteer pullers will gather at 8 a.m. June 25 at the west end of Chiawana Park for instructions. After several hours of dedicated pulling, volunteers will be provided with lunch in the park. Cans for weed disposal will be provided along the trail, but you'll want to bring thick gloves to protect your hands.

To sign up, contact Dan Dotta with the city of Pasco at 509-543-5757. Sections of the pathway are also up for "adoption" to keep them clear of puncturevine through the season.

* Marianne Ophardt is a horticulturist for the Washington State University Benton County Extension.

This story was originally published May 28, 2011 at 3:00 AM with the headline "Puncturevine is nasty weed ."