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Invasive Weeds of the Lake Tahoe Basin
Invasive weeds are aggressive plants that have been introduced into an environment outside of their native range. Sometimes referred to as alien species, these weeds have been separated from the natural enemies that help control them in their homeland. They grow rapidly, reproduce profusely, and compete with native plants for water, light, and nutrients. Some of these weeds have been designated as noxious by California and Nevada law, requiring control efforts by property owners.
Invasive weeds tend to outcompete native plants, especially where lands have been disturbed. When they displace native plants and animals, they lower diversity, reduce hunting and fishing potential, change the aesthetics of a habitat, inhibit recreational activities and tourism, crowd out endangered species, and reduce forage value. At Lake Tahoe, weeds that have coarse or shallow root systems, such as perennial pepperweed and dalmatian toadflax, increase soil erosion and threaten lake clarity.
This guidebook will help you identify the invasive weeds threatening the Lake Tahoe Basin. Common “look-alikes” are also included to help you differentiate between desirable native plants, noted J, and undesirable invasives, designated L. Plants that could potentially become invasive are marked as K. You may choose to avoid planting these species on your property. Information on management is also included for each invasive weed, as is the noxious weed status in Nevada and California. California’s noxious weed rating system designation, which is based on distribution of the weed, is also provided. “A” rated weeds are normally limited in distribution throughout the state; “B” rated weeds are more widespread; and “C” rated weeds are widespread throughout the state.
n Flowers: single flower heads grow at ends of branches; bracts are lined in black
Perennial June to August Pull or dig before seed production; herbicides are available
n Flower color: white with yellow center
Nevada-NO; California-NO 44
Leucanthemum X superbum LESU49
Plant, Brenneman; Flower, Donaldson
Upper leaves serrate and sessile; smaller toward top of stem Approximate disk flower to ray flower ratio
Rosette leaves oval; margins serrate
n Height: 1 - 3 ft, tends to be 6 - 12 in; taller than oxeye daisy Also Known As Origin Habitat Life Cycle Flowering Time Management Noxious Weed List
n Stems: stiff, more-or-less smooth
None Nonnative, naturalized
n Leaves: upper, serrate and sessile; lower, petiolate
Well-drained soil, full sun, ornamental gardens
n Flowers: single flower heads grow at ends of branches; heads larger than oxeye daisy
Perennial July to September None; recommended garden flower
n Flower color: white with yellow center
Nevada-NO; California-NO 46
KLAMATHWEED Hypericum perforatum HYPE
5 separate petals Occasional tiny black dots at edges of petals
Transparent dots on leaves
n Height: 1 - 3+ ft Also Known As Origin Habitat Life Cycle
Nonnative, invasive Pastures, meadows, roadsides, waste areas
n Branches: somewhat 2-ridged and woody at the base
June to late September
Pull or dig repeatedly; chemicals are available
Noxious Weed List
n Stems: erect with numerous rust-colored branches
St. John’s Wort
n Leaves: elliptic to oblong, entire, opposite, sessile; not over 1 in long n Flower color: yellow
Nevada-YES; California-YES, C-rated 48
SCOTCH BROOM Cytisus scoparius CYSC4
Numerous showy pea-like flowers Flattened, hairy, brown to black seed pods
Upper leaves simple and entire
Lower leaves 3 leaflets, hairy
Branches: many leafless or have few leaves Also Known As Origin Habitat Life Cycle
n Height: woody shrub up to 10 ft
n Stems: hairy when young, then generally smooth; most sharply 5-angled or ridged
Nonnative, invasive Pastures, forests, waste areas Perennial June to August
n Branches: dark green; more-or-less erect
Cut stems at ground level in late summer; pull seedlings; dig plants; use weed wrench to remove root; herbicides are available
n Leaves: upper, simple and entire; lower, 3 leaflets, hairy
Noxious Weed List
Nevada-NO; California-YES, C-rated
n Flower color: pale to deep yellow 51
Alternate: Borne singly at each node, such as leaves.
Ovate Leaf: Egg-shaped leaf that is attached at the broad end.
Axil: The point formed between the stem and any part, such as a leaf, attached to it. Bract: A modified leaf at the base of a flower.
Panicle: A branched inflorescence in which the flowers bloom from the bottom up.
Corymb: A flat-topped or round-topped arrangement of flowers where the lower flower stalks are longer than the upper stalks.
Petiole: The stalk of a leaf. Pinnate: A compound leaf with leaflets arranged on opposite sides of the axis.
Cyme: A flat-topped or round-topped arrangement of flowers in which the terminal flower blooms first.
Raceme: A simple, elongated arrangement of flowers.
Crenulate: Having very small, rounded teeth on the leaf margin. Disk flower: The tiny, tubular flower of the Asteraceae that forms the center disk of the flowerhead. Divided: Deeply lobed leaf in which lobes are indented to the base or the midrib. Elliptic: Shaped like an ellipse or a narrow oval, broadest in the middle. Entire: The margins are smooth, without teeth or lobes. Inflorescence: A flower cluster. Linear: Narrow and flat with sides or edges parallel, as in a leaf. Lobed: Bearing lobes cut less than halfway to base or midvein. Margin: The outer edge of the leaf, which may be smooth, serrated, lobed, etc.
Ray flower: The long, narrow flower that radiates outward from the disk flower in the Asteraceae family. Each ray flower resembles a single petal. Rhizomatous: Having rhizomes, or horizontal underground stems that produce shoots above and roots below. Rosette: A dense, basal cluster of leaves arranged in a circular fashion around one point, usually at ground level. Serrate: With sharp teeth directed forward; generally refers to leaf edges. Sessile: Without a stalk of any kind; for example, a leaf directly attached to a stem. Spatulate: Shaped like a spatula, with a rounded blade that tapers to the base. Spike: An unbranched, long flower stalk in which the flowers attach directly to the stem and mature from the bottom upwards.
Midrib: The middle vein of a leaf.
Toothed: Having sharp points or lobes along a margin, as on a leaf.
Oblong: Leaf shape in which the leaf is two to four times longer than it is wide, with nearly parallel sides.
Umbel: A flat-topped flower arrangement.
Opposite: Leaves or other structures borne across from each other at the same node. 52
Winged stem: A stem with one or more thin, flat margins protruding along the length of the stem. 53
The Lake Tahoe Basin Weed Coordinating Group has been mapping weeds in the basin since 2002. Regular mapping and inventory helps us determine which species are present in the basin, what management methods are appropriate, and whether management has been a success. We can also track patterns of spread and plan preventive practices. We welcome your mapping information. Please include:
Nevada Douglas County Weed District (775) 782-9835 Washoe County Weed Hotline (775) 325-6989 California Nevada County Agriculture Department (530) 273-2648
• the date surveyed
Placer County Agriculture Department (530) 889-7372
• the weed name and code (preferably the scientific name)
El Dorado County Agriculture Department (530) 621-5520
• the latitude and longitude of the observation if available. If using a global positioning system (GPS) unit, set your meter to datum NAD83 and decimal degrees. • a thorough description of the location • the size of the infestation in square feet or acres • the density of the infestation (number of plants or estimated percent cover)
Funded by: The Lake Tahoe License Plate Program, Nevada Division of State Lands Nevada Department of Agriculture
• any control methods you employed Please do not take any management actions or remove plants until they have been positively identified. Consult your county weed contact for assistance. Forward the data to the appropriate county. See listings on next page.