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. If you find an invasive weed, please report the infestation to the appropriate county (see contact numbers on the inside back cover) or go online to www.tahoeinvasiveweeds.org and complete the reporting form.
How to Use the Guidebook 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 , and undesirable invasives, designated . Plants that could potentially become invasive are marked as . You may choose to avoid planting species that may become invasive on your property. Information on management is also included for each invasive weed, as is the noxious weed status in Nevada and California. “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. Relative abundance of each species is provided. Widespread: Found at numerous locations in the basin Moderate:
Found at several locations; large populations may occur at a few locations
Only at one or a few locations; no large populations
Funded by: Lake Tahoe License Plate Program & Nevada Division of State Lands
Nevada Department of Agriculture
US Forest Service, State and Private Forestry Program
Preventing the Spread of Weeds Prevention is the least expensive and most effective way to halt the spread of noxious and invasive weeds. This requires: • Educating workers and the public about the importance of managing weeds on an ongoing basis; • Properly identifying weed species; • Avoiding or treating existing weed populations; and • Preventing weed seeds or other plant parts from establishing new or bigger populations.
Steps you can take: 1. Use this book to identify invasive weeds in your area. 2. Inspect your work or play area. Identify any invasive weeds, map the location of the weeds and avoid these areas. 3. Clean vehicles, shovels and other soil-disturbing equipment prior to entering a site to avoid introducing weeds. 4. Don’t introduce weed-contaminated soil, fill, or other materials to new sites. Use certified weed-free products. 5. Check shoes, clothing, bicycles and vehicles regularly for weed seeds or other plant parts. Carefully remove and dispose of weedy materials. 6. Pressure-wash vehicles and equipment after driving in weedy areas. Periodically monitor and treat areas to prevent weedy plants from establishing. 7. Establish a decontamination area such as a tarp for cleaning clothing and equipment. 8. Don’t walk, ride or drive through infestations. When operating vehicles, stay on established roads or trails. 9. If dogs accompany you, check their paws and coats for weed seeds and other plant parts and remove them. 10. Don’t plant invasive weeds in your garden or landscape.
Leaves: ovate, alternate and entire; succulent and waxy
Life Cycle Perennial Flowering Time July to fall
Growth form: more scattered than yellow toadflax
Relative Abundance Moderate Management Pull or dig for several years, removing as much root as possible; do not mow; chemical control is available Noxious Weed List Nevada A-rated; California A-rated 40
Flower color: yellow, with orange, bearded throat 41
n Leaves: conspicuously veined; stem leaves lanceolate and up to 10 inches long
Life Cycle Tap-rooted biennial Flowering Time July to fall
Relative Abundance Infrequent
n Growth form: erect
Management Dig or hand-pull, removing as much root as possible; herbicides are available
n Flower color: lavender to purple, rarely white
Noxious Weed List Nevada-NO; California-NO 62
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.
Palmate: Having three or more veins or lobes radiating from a central point, similar to the fingers on a hand.
Corymb: A flat-topped or round-topped arrangement of flowers where the lower flower stalks are longer than the upper stalks.
Panicle: A branched inflorescence in which the flowers bloom from the bottom up. Petiole: The stalk of a leaf.
Cyme: A flat-topped or round-topped arrangement of flowers in which the terminal flower blooms first.
Pinnate: A compound leaf with leaflets arranged on opposite sides of the axis.
Crenulate: Having very small, rounded teeth on the leaf margin.
Raceme: A simple, elongated arrangement of flowers.
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. Midrib: The middle vein of a leaf. Oblong: Leaf shape in which the leaf is two to four times longer than it is wide, with nearly parallel sides. Opposite: Leaves or other structures borne across from each other at the same node.
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. Toothed: Having sharp points or lobes along a margin, as on a leaf. Umbel: A flat-topped flower arrangement. Winged stem: A stem with one or more thin, flat margins protruding along the length of the stem. 65
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.
To report a weed sighting online, or to contact the Lake Tahoe Basin Invasive Weed Coordinating Group, go to www.tahoeinvasiveweeds.org.
We welcome your mapping information. Go to www. tahoeinvasiveweeds.org and complete the reporting form. You’ll also find additional photos and information about invasive weeds, plus maps showing locations of known infestations in the Lake Tahoe area. When collecting data, please include: • the date surveyed • the weed name and code (preferably the scientific name) • 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) • 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. tahoeinvasiveweeds.org 66