Reduce your blackberry thicket to a few stragglers

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Last Updated: 
July 1, 2008

MCMINNVILLE - It could take years to eradicate a large patch of blackberries, because so many seeds remain in the soil. But with good timing and dedication property owners can reduce a sprawling blackberry thicket to a few manageable stragglers, according to Susan Aldrich-Markham, agronomist for the Yamhill County office of the Oregon State University Extension Service.

On her own creek-side property, Aldrich-Markham has been trying all kinds of methods for more than 10 years and advising rural landowners what they can do to control blackberry vines.

Contrary to the notion that the blackberry is as native to Oregon as rain, this hardy relative of the rose is an introduced plant by the famous Luther Burbank (1849-1926).

He is honored for developing more than 200 varieties of fruits and vegetables, including 166 varieties of plums and the russet Burbank potato. But the western European blackberry that Burbank introduced in 1885 as "Himalayan giant" has become a giant problem. A single blackberry cane can produce a thicket six yards square in less than two years.

In 119 years, the Himalayan blackberry's classification has changed from tasty berry to noxious weed as it has choked out native vegetation from northern California to British Columbia.

According to Aldrich-Markham, several control methods can work well, as long as those preparing to battle blackberry vines are armed with information about the benefits and drawbacks of the most common methods. Listed here, they range from organic to chemical:

  • Digging up, or plowing under can eliminate existing plants, but it also creates an ideal seedbed for the next generation. It brings blackberry seeds close to the surface, so hundreds of new seedlings can spring up. Digging is most effective on small, highly managed plots, where sprouts can be dug up before setting deep roots. Planting a perennial, such as grass, in the area will help because it provides competition with new weed seedlings and the soil surface is no longer disturbed to bring up new seeds. Aldrich-Markham says this is the best practice for long-term control.
  • Goats or mechanical mowing both work by removing the leaves so the plant can't turn sunlight into food. The root eventually starves. Both goats and mowers must be brought back often, and both have the same drawback: They also mow down everything else in their path.
  • Round-up, and other similar glyphosate herbicides, work effectively on blackberry plants only if applied in the fall. That is the only time the plant diverts its food reserves down to its roots rather than up to its leaves and shoots. The herbicide moves in the plant with the food.
  • Crossbow is an excellent herbicide for killing woody brush such as blackberry plants, Scotch broom and poison oak. It is a mixture of 2, 4-D and triclopyr. The triclopyr is the most effective ingredient.

    Crossbow will work on blackberry plants any time of the year, and it will not kill grass. Contrary to some popular misinformation, it is best NOT to cut down the blackberry plants first, unless the plants are too big to reach with spray equipment. Cutting down the plant reduces the leaf area, which can absorb the herbicide, so the plant may not take enough in to kill the large root. The best time to apply this chemical is in the late spring when the plant stems are fully extended.

    The downside is that Crossbow is oil-based, which means when the weather is warm, the herbicide can evaporate and drift onto adjacent vegetation or into creeks. Some volatilization (evaporation) can occur at temperatures as low as 60 degrees. Take care to apply on a cool, cloudy day. Grapes and maple are particularly sensitive to Crossbow drift. If sensitive plants are growing in the area, Crossbow should only be applied in the fall when these plants are less sensitive.

  • The herbicide Garlon 3A is triclopyr alone in a water-based formulation. Unfortunately, this is only sold in two-gallon containers, said Aldrich-Markham.

No matter if you've grubbed, chopped, or sprayed, after you've gotten rid your blackberry plants, don't forget to plant hardy alternative vegetation, so the new plants crowd or shade out any new blackberry seedlings.

"You can't treat a patch of blackberry and then walk away," Aldrich-Markham said. "All the control methods can take several years at least to eradicate a large patch. Don't take a break and let the blackberries regain their strength."

Author: Peg Herring
Source: Susan Aldrich-Markham