Black locust (Robinia pseudoacacia)

Description:

Appearance: Fast growing tree up to 75' in height with deeply furrowed with flat-topped ridges. Seedlings and root sprouts have long thorns and grow rapidly.

Leaves: Alternate, pinnately compound (leaflets on both sides of a common stalk) with 7- 21 elliptic, untoothed leaflets, with one leaflet at the tip. A pair of short, sharp thorns sit at the base of each leaf where it is attached to the twig.

Flowers: Fragrant, drooping white flowers arranged in elongated clusters appear in late May and June.

Seeds: Seed pods are smooth, 2 - 4" long; they mature in September and persist through winter.

Roots: Extensive fibrous root system. Spreads vegetatively through root suckering and runners.

Ecological Threat:

  • Invades primarily disturbed habitats, degraded wood, thickets and old fields crowding out native vegetation of prairies, oak savannas and upland forests, forming single species stands.
  • It reproduces vigorously by root suckering and stump sprouting forming a common connecting root system.
  • It is native to the U.S. and occurs naturally on the lower Appalachian mountain slopes. It has been extensively planted for its nitrogen-fixing qualities and its hard wood.
  • Black locust is a MDA Restricted noxious weed in Minnesota.

 

Control Methods:

Mechanical

  • Mowing and burning is only temporarily effective because of the tree's ability to resprout and spread vegetatively

Chemical

  • Cut-stump treatment with glyphosate; cut-stump or basal bark spray treatment around the stem with triclopyr
  • Foliar spray in single species stands with glyphosate or clopyralid

 

Native Substitutes:

Additional Resources