About Common Fennel:

Closely related to domestic garden fennels, common fennel is a large, aromatic, perennial with upright, branched stems, growing up to 7 feet tall, with a very large taproot. The fern-like If you would like weed identification, foliage, as well as stems, roots, and seeds are site-specific control recommendations, Common Fennel hairless and all have a strong licorice scent. or additional noxious weed information, (Foeniculum vulgare var. vulgare) The finely divided leaves have a triangular contact the San Juan County Noxious Weed Control Program. arrangement and are dark green to bronze. Leaf stems are swollen, fleshy and have a wid- ened base. The small, yellow flowers form an Class B Noxious Weed umbrella-shaped cluster and bloom from May to

September. Plants reproduce from thousands of seeds and fragments of root crown. (Control required in San Juan County) Why control Common Fennel?

Common fennel rapidly spreads by seed, form- ing dense, monotypic stands that overtake native plants and habitats critical to wildlife and pollinators, as well as gardens and land- scaping. Plants can be difficult to control once San Juan County Noxious established. In San Juan County, mature plants Weed Control Program harbor great numbers of invasive snails that 2020 further threaten native plant populations.

Before you begin:

Create a plan for restoration before removing weeds or disturbing the soil. Common fennel seeds germinate easily on bare soil, but have a P.O. Box 1634 more difficult time in established vegetation. If or enough desirable vegetation is not present to 62 Henry Road #26 replace the fennel, newly exposed soil can be Eastsound, WA 98245 sown with native plants or non-invasive peren- (360) 376-3499 nial grasses to promote competition.

Common Fennel vs. Other Apiaceae: [email protected]

Common fennel displays traits similar to other [email protected] species in the carrot (Apiaceae) family, most notably domestic fennel and dill, but can be distinguished by its much greater size, woody (not https://extension.wsu.edu/sanjuan/noxious/ bulbing) stem bases and root crown, and perennial lifecycle. Photo credit: Rich Lee (SJC NWCP, retired) Persistent, woody, dead canes may be associated with older plants. Proper identification of Special thanks to the WA State & King County the species you wish to control Noxious Weed Control Boards and will help you choose the best The Nature Conservancy. management practices. Florence Fennel (Foeniculum vulgare v. azoricum) Photo credit: WA NWCB Burning: Although fire alone will not control Follow-up Common Fennel Control fennel, burning followed by herbicide treatments Monitor and eradicate new populations for at By law, herbicides must be used in strict has achieved eradication in some cases. least 7 years, while keeping established accordance with label instructions. Biological Control infestations from spreading into non-infested Research on effective and safe herbicide use is on-going and often Due to potential negative effects to cultivated or recently controlled areas. Always purchase contradictory. For more recent information contact the San Juan weed-free seed, mulch, soil, and hay for County Noxious Weed Control Program. fennels, there are no biocontrol agents available for use in the United States. restoration purposes and whenever else Timing possible.

Livestock grazing does not control fennel and Common fennel control is most effective when may spread or worsen infestations. Debris Removal: If cut before flowering, done in early summer, when plants are form- leave onsite or dry and then compost. Do not Chemical Control ing tight buds prior to blooming. compost roots. If flowering, first remove and Always follow label instructions to find the correct bag the flower heads and dispose of them in Tools for Common Fennel removal: herbicide concentration and timing for your site the trash. Burning is also an option if  Work gloves and the method you plan to use. permissible and material is dry.  Shovel, mattock Timing: Fall treatments are generally more Site Restoration: Establish dense,  Mower (brush), string trimmer, or scythe effective, since most herbicides move more competitive native or other non-invasive  Pruners & plastic bag or bucket (for seeds) efficiently into roots when the days are shorter, vegetation. Immediately re-seed bare ground Herbicide & proper protective equipment,  soil is moist, and temperatures are cooler. Avoid areas with native plants and/or non-invasive if appropriate treating old or drought-stressed leaves, or when perennial grasses after removing dense Repeatedly removing or treating all plants the soil is dry. Herbicide treatment may be fennel infestations to reduce erosion and within a site will help prevent continued seed enhanced when fennel is cut in late summer, and subsequent weed establishment. production and re-sprouting from the roots. then spot sprayed later in the fall when plants are Non-Invasive & Native Substitutes Apply a combination of methods (manual, again in the rosette stage. Low growth may be for Common Fennel cultural, and/or chemical) to increase the shielded from herbicide applications if debris is If you enjoy Common Fennel, please consider success of control. not removed prior to treatment.

instead growing one of many non-invasive Manual & Mechanical Control Spot Spray: Triclopyr, glyphosate, and 2,4-D relatives and cultivars. The biennial Florence Digging/Pulling: Due to the extensive tap- applications to fully developed leaves, but before fennel (Foeniculum vulgare v. azoricum) has root, manual removal is often labor intensive. flowering, are effective. Applications are less equal or superior flavor and also produces a Seedlings and very small plants can be dug effective after plants have bolted. Triclopyr vegetable leaf base. Annual dill (Anethum applications typically provide the best results. out, removing as much taproot as possible to graveolens) can also be substituted for its prevent re-sprouting. Mature root crowns can Unlike glyphosate, triclopyr and 2,4-D are broad- culinary value. Both will provide very similar be removed with a mattock. leaf selective herbicides that can be used in yellow flowers and lacy foliage in garden Cutting/Mowing: Cutting and mowing pasture and meadow settings without damaging settings, as well as forage for butterfly larvae. grasses. Adding a dye marker to the mixture can mature plants just prior to flowering can even- For substitution in open, natural settings, the tually deplete underground energy reserves, help reduce the amount of herbicide used. Always follow native Spring Gold (Lomatium utriculatum), a but may need to be repeated multiple times low-growing perennial, provides similar per year for several seasons. Mowing when all label instructions. Adding a non-ionic surfactant to the flowers, foliage, and high quality forage and plants are in flower or seed will further spread habitat for a variety of native pollinators. the infestation. mix may improve herbicide spread and penetration. Cultural Control Cut Stem: In either the Cultivation: On appropriate sites, deep tight bud stage or in early fall, cultivation will kill mature plants. Repeating apply triclopyr or glyphosate cultivation as necessary can deplete or greatly directly to the outer edge of reduce seed bank populations. freshly cut stems. Cut stem Mulching: Seedlings and small plants can be applications should be made controlled by sheet mulch in some cases. Common Fennel foliage immediately after cutting to Dill (Anethum graveolens) Spring Gold (Lomatium utriculatum) Rich Lee, SJC NWCP (retired) ensure effectiveness. Photo: Ansel Oommen, Bugwood.org Photo: University of California, Irvine