Invasive Species

Summer student Tess shows just how big puncturevine can get in one season.

While it may seem repetitive to my regular readers, I would be seriously remiss if I didn’t write an article on the spiny annuals we love to hate.

Unlike most of us humans, puncturevine and longspine sandbur are basking in the summer heat; although fortunately they are not flourishing as much as usual, undoubtedly due to the lack of rain.

Both of these species are summer annuals. This means they emerge in the spring or early summer, grow during the summer, produce seed in mid to late summer and are killed by frost in the fall.

Puncturevine is native to the southern Europe and Mediterranean region. Since its initial discovery in Washington State in 1924, human activity has introduced and spread the plant throughout the Pacific Northwest. In Canada, puncturevine is known to occur only in the Okanagan and lower Similkameen valleys. It is most prolific in the sandy soils around Oliver, Osoyoos and Keremeos, with a few dozen sites around Penticton, and isolated patches as far north as Vernon.

Longspine sandbur, also known as burgrass or field sandbur, is an invasive grass that is native to North America. It originated in the subtropical regions of the continent and is therefore not considered an indigenous species of our region.

It only occurs in the Okanagan Valley, with the most northern occurrence being at the southern end of Penticton. Small patches have recently been identified in the Boundary region near Christina Lake, which indicates that this invader is most certainly on the move.

Both species grow along road shoulders, gravel trails, vacant lots, beaches and unpaved parking sites. Puncturevine is mat forming, with stems reaching up to 3 metres in length. It readily makes its way into agricultural lands, where it grows between rows of ground crops such as strawberries, tomatoes and melons, tree fruits, and grape vines.

The stems are covered by hairy leaves that are divided into six to eight leaflets.

Longspine sandbur typically grows upright, reaching heights of 0.75 m, but can branch and spread flat along the ground. Leaf sheaths are flattened, very loose, and have a tuft of short hairs where they join the blade.

The fruits or seedpods are the most distinctive characteristic of both species. Puncturevine seedpods consist of five sections that, at maturity, break into tack-like structures with sharp spines for which this weed is aptly named.

These sharply pointed seedpods stick painfully in bare feet and flatten bicycle tires, reducing the recreational potential of many areas. Even light truck tires can be punctured by the seedpods.

Longspine sandbur is also spiny, but in this case the seed itself is round and spiky, and quite large, measuring up to 6 mm wide.

Dogs are not immune from the seeds of these spiny invaders which can lodge into your canine’s paws. The seeds of both species can also injure the feet, hides, mouths, eyes and digestive tracts of livestock.

Both species can be contaminants of fill, gravel, sand, crushed stone and other aggregates, so be wary if you are importing such materials to your property.

The best method of controlling these invaders is to prevent establishment by destroying the first plants found in an area before seeds begin to form. Because they germinate all summer long, monitoring and repeat treatments are continually required.

Young plants are easily controlled by hoeing, shallow tillage or by carefully hand-pulling plants. Daisy (dandelion) grubbers are a great tool for popping up puncturevine plants.

If seedpods have not yet developed, the plants can be composted. If plants have already matured and the seedpods have ripened (turned brown and easily fall off the plants), plants should be carefully pulled and bagged, then taken to the local landfill.

Like most other weeds, puncturevine and sandbur prefer areas of disturbed, bare ground. So remember to reduce areas of soil disturbance and re-seeded immediately with a suitable dryland seed mix.

A three-inch layer of mulch can also effectively reduce infestations of puncturevine.

For information on invasive species go to www.oasiss.ca or contact the Program Coordinator for the Okanagan-Similkameen, Lisa Scott, at 250-404-0115.

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