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Buckthorn keeps coming back

Fri, Nov 5th, 2010
Posted in Agriculture

Buckthorn is not the only invasive species we have in southeast Minnesota, but having seen and heard Angela Gupta, University of Minnesota Regional Extension Educator for Forestry, at both the Woodland Advisor-Tree ID class near Caledonia and the Small Farm U in Winona, it is the most talked about.

Most of the native trees and shrubs found in woodlots, fencerows, windbreaks and forest edges have lost their leaves. There is one exception; the leaves of common buckthorn are still green and clinging to the branches and twigs of the plants. The green leaves on large masses of buckthorn make it easy to see just how invasive this woody plant is.

Adding to its invasive qualities is the fact that it serves as an alternate host to crown rust of oats and as an overwintering site for the soybean aphid. Soybean aphids lay their last eggs of the season on buckthorn plants, leaving them to overwinter and hatch in the spring.

Common buckthorn has dark green leaves with curved main veins that remain green in the fall after other species have lost their foliage. The twigs are tipped with a short, sharp thorn and the female plants produce blue-black berries that have numerous seeds. The berries are toxic to humans but are readily eaten by birds and, having a laxative effect, the seeds are readily spread from place to place.

Late autumn and winter is an excellent time to control common buckthorn. It is easy to identify because of its green leaves and chemical treatments are more effective when the buckthorn plants are storing energy.

If there are only a few buckthorn plants and they are small enough, hand pulling is the best way to remove them. A tool such as a "Weed Wrench" can be used to remove buckthorn stems up to 2 ½ inches in diameter. If they are too numerous to pull or dig, the foliage can be sprayed with a product like Garlon 3A which is a Triclopyr amine formulation that is mixed with water or any of the Triclopyr products that are available from local sources (Bush-B-Gone, Brush and Stump Killer and others). Glyphosate (Roundup and similar products) can also be used for foliar applications on seedlings, but is non-selective and will kill all vegetation.

If the plants are too large for foliar application, cut them off at a height of six inches or less from the ground and treat the stumps with Triclopyr or Glyphosate to prevent resprouting. When using Triclopyr, treat only the cut surface using a wick applicator, sprayer or paintbrush. When using Glyphosate, treat the cut surface and the stump back to the soil line.

Yet another method is to use an ester formulation of Triclopyr that has been mixed with a diluent and apply it directly to the bark at the base of the tree. This can be effective on trees up to six inches in diameter if the chemical is applied to the lowest 1 ½ feet of the bark around the entire circumference of the tree. If the tree is less than two inches in diameter, the amount of the base of the tree for application can be cut in half. Larger trees can also be wounded near the base with an ax to create a frill and then treated with the chemical. Garlon 4, Crossbow or Pathfiner II are effective chemicals containing the ester form of Triclopyr for basal bark treatment.

The commercial products listed in this article are for your information. No endorsement by University of Minnesota Extension is intended.

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