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Herb Robert

Botanical Name:

Geranium robertianum

Class B Noxious Weed

General

  • Herb Robert is both a winter and a spring annual or bienennial. It is a low growing plant that is hairy and shallowly rooted. Plants have a pungent odor when crushed.

Identification

  • Flowers have 5 pink petals.
  • The leaves are deeply dissected and light green. The foliage turns red in late fall.
  • The stems are upright to spreading, hairy and turn red in high light conditions.
  • The fruit is a capsule. Seeds are brown and about 2 mm in length.

Photos

Photos: WA State Noxious Weed Control Board

Habitat

  • Found in moist forests with canopy closure and on dry rocky outcrops.
  • It is also becoming a significant garden pest in some areas.
  • It is found from sea level to mid-mountainous areas in both the Cascades and Olympics.

Reproduction and Spread

  • Reproduces by seeds.
  • Seeds are ejected in response to drying of the capsule.
  • Reports indicate that they may be ejected as far as 15 to 20 feet from the mother plant.

Control

  • Easy to hand-pull.
  • Herb Robert has a very shallow, weak root system which makes hand pulling easy.
  • Aim to pull plants before they go to seed as seeds can survive in the soil for a number of years.
  • Frequently monitor sites and control as needed.
  • Plants can be mowed or cut back with a string trimmer or weed whacker early in the season before they flower.

Chemical Control

Glufosinate, glyphosate, imazapic, imazapyr, metsulfuron, sulfometuron, and triclopyr + 2,4-D gave promising results in initial trials.

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