Canada goldenrod (Solidago canadensis) is a perennial plant that thrives mostly in moist conditions and is fairly intolerant of shade. This species reproduces from seed and its flowers are self-incompatible, which means it favors outcrossing for reproduction. Canada goldenrod is considered an important source of nectar for honeybees.
Canada goldenrod infestation
Photo by Bonsak Hammeraas of The Norwegian Institute of Bioeconomy Research via Bugwood.org
Identification
Seedlings: Cotyledons of canada goldenrod are approximately 5 mm (0.2’’) and elliptic. Young leaves form a basal rosette and are long, with bases which narrow into a short stalk and toothed margins.
Canada goldenrod seedling
Photo by Ohio State Weed Lab of The Ohio State University via Bugwood.org
Canada goldenrod seedling
Photo by Ohio State Weed Lab of The Ohio State University via Bugwood.org
Leaves: Leaves of the mature plant are alternate, sessile, and lanceolate. They taper at the base, have mostly-toothed margins, and become gradually smaller up the stem. Leaf blades are smooth on the upper surface and hairy on the bottom. They also grow crowded along the stem.
Canada goldenrod mature leaves
Photo by Bruce Ackley of The Ohio State University via Bugwood.org
Canada goldenrod mature stem and leaves
Photo by Robert Videki of Doronicum Kft. via Bugwood.org
Mature plants: The stems are erect, slender, and mostly unbranched with soft, short hairs (at least in the upper-half portion). They grow up to 2.1 m (7 ft) tall.
Canada Goldenrod stem
Photo by Rob Routledge of Sault College via Bugwood.org
Mature canada goldenrod plant with flowers
Photo by Charles T. Bryson of USDA Agricultural Research Service via Bugwood.org
Flowers/Fruit: Flowers emerge from August through October. Flower are yellow and grow in a pyramid-like formation with composite heads. Each flower is made up of 10-17 yellow ray petals surrounding 2-8 yellow disk flowers. Tiny leaf-like structures that tuck under the flowers (bracts) are yellow with a green pointed tip and 2-4 mm (0.08-0.2”) long. A pappus of white hair-like structures is attached to the achenes (fruits) which are 1 mm long (0.04”).
Canada goldenrod flowers
Photo by Mary Ellen Harte via Bugwood.org
Canada goldenrod flowers
Photo by Mary Ellen Harte via Bugwood.org
Management
Chemical control
More information to come on chemical management of Canada goldenrod.
Non-chemical control
Due to its ability to reproduce from its root systems, canada goldenrods are among the more difficult weeds to manage. Effective management has mainly been shown in consistent and timely application of herbicides. Mechanical management is not commonly used, although mowing in intervals will eventually eradicate the weeds. If using this method, allow plants to regrow 0.2-0.3 m (8-12”) between mowing sessions. In addition, to mitigate seed dispersal, remove flower heads before the seed(s) ripen.
References
Uva R H, Neal J C, DiTomaso J M. 1997. Weeds of the Northeast. Book published by Cornell University, Ithaca NY. The go-to for weed ID in the Northeast; look for a new edition sometime in 2019.
Cornell University’s Turfgrass and Landscape Weed ID app. Identification and control options for weeds common to turf, agriculture, and gardens in New York; uses a very simple decision tree to identify your weed.
The Fire Effects Information System’s webpage of Index of Species Information for canada goldenrod. Provides a wide range of information regarding canada goldenrod including Botanical and Ecological Characteristics and Management Considerations.
Province of Manitoba’s official webpage on guidance to Weed Control in Pastures. Includes instructional descriptions of weed control for different stages of life and locations.
The USDA and NRCS (Natural Resources Conservation Service) Plant Guide for canada goldenrod. This web guide offers extensive information on canada goldenrod, including its distribution, ecological uses, and adaptation.