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Common Fennel

Botanical Name:

Foeniculum vulgare

Class B Noxious Weed

General

  • Escapes cultivation and quickly establishes dense infestations that crowd out native plants that are critical to wildlife habitats.
  • May pose a threat to native grasslands.

Identification

  • A large, aromatic, perennial herb.
  • Can grow up to 6.7 feet tall (2 meters) and has a very large taproot.
  • Foliage, stems, roots and seeds are hairless and all have a very strong licorice scent.
  • Flowers are small and yellow and form an umbrella shaped cluster.
  • Plants bloom from May to September.
  • Leaves have an overall triangular shape and are many times divided into thin, featherlike leaflets and are dark green or bronze.
  • Leaf stems (petioles) are swollen and fleshy and have a widened base.
  • Stems are upright and branched.
  • Seeds are about 0.15 inches (3.5 to 4 mm) long and have small ridges.

Photos

Habitat

  • Found along roadsides, in pastures, prairies, streamsides, coastal bluffs as well as wetland areas..

Reproduction and Spread

  • Reproduces from seed.
  • Can also reproduce from pieces of the root crown.

Control

  • Can be controlled using mechanical techniques as well as herbicides.
  • Small infestations can be hand pulled but mature plants are difficult to remove because of the taproot.
  • Above ground growth can be repeatedly cut prior to flowering to deplete below ground energy reserves. This technique may need to be down for several years to be successful.
  • Cutting above ground growth when flowers are present may promote seed dispersal.

Chemical Control

2, 4-D amine

  • Spot treatment: 0.25 to 0.5% solution
  • Apply in spring to fully-grown leaves but prior to flowering.
  • 2, 4-D is usually not able to fully control common fennel, so combining with other products is generally recommended. Retreatment will likely be necessary.
  • Avoid drift to sensitive crops.

Glyphosate

  • Rate: 2.8 lb ae/a
  • Apply in spring to fully-grown leaves but prior to flowering.
  • Adequate foliar coverage of fennel foliage is necessary. Add nonionic surfactant if not included in the formulation.
  • Glyphosate is nonselective and injures or kills other vegetation in the treated area.

Triclopyr

  • Broadcast treatment: 1 to 2 lb ae/a; spot treatment: 0.5 to 1% solution.
  • Apply in spring to fully-grown leaves but prior to flowering.
  • Do not drift onto sensitive crops.
  • Do not contaminate water.
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