Noxious Weeds

What Is a Noxious Weed? Noxious weeds are non-native invasive plants that, when introduced, quickly dominate the landscape. The legal definition is “any species of plant that is, or is likely to be, detrimental or destructive and difficult to control or eradicate.”

Why You Should Care About Noxious Weeds

Did you know that a single Tamarisk tree can use up to 200 gallons of water per day!?
Russian knapweed plants are poisonous to horses, and their leaves and roots are allelopathic, which means they can actually prevent other plants from germinating!
Leafy spurge plants can eject their seeds up to 30 feet and their sap causes blisters in the mouths of cattle and horses.
Cheatgrass (Bromus tectorum) is an example of a non-native noxious weed that is now beyond control. It has invaded up to 17 million acres in the United states and is the most common plant species in Nevada.
With the invasion of cheatgrass in the Great Basin, wildfire intensity and frequency has increased. The increase in wildfires destroys sagebrush plant communities, which many sensitive wildlife species, including sage grouse, Brewer’s sparrow, pygmy rabbit and the sagebrush lizard, need to survive.

These are just a few examples of why everyone who shares in the appreciation and stewardship of our beautiful public lands should care about noxious weeds!

Volunteer with our team out in the field and build your land stewardship knowledge »

What You Can Do About Noxious Weeds

The best way to help control the spread of noxious weeds is through prevention!

First, of course, you need to know what you’re looking for. The Nevada Noxious Weed Field Guide is a great resource for identifying noxious weeds in northern Nevada.

Many weeds are spread by animals and vehicles, particularly vehicles taken off roads. Be sure to clean your vehicle, OHV, boots, and camping equipment between adventures. If possible, clean the tires and undercarriage of your vehicle when you move from one area to another.

If you find a suspected noxious weed in Black Rock country, photograph the species, record the GPS coordinates or a detailed locality description and report it to our email: info@blackrockdesert.org.

If you really want to learn about noxious weeds and explore the High Rock Canyon area, join Friends’ for a weekend of noxious weed mapping.

Noxious Weeds That Could Show up in the Black Rock High Rock Region

Noxious weeds are classified as A,B or C (Nevada Revised Statutes 555.005).

Category A weeds are weeds that are generally not found or that are limited in distribution throughout the State. Such weeds are subject to:

Active exclusion from the State and active eradication wherever found.
Active eradication from the premises of a dealer of nursery stock.

Category B weeds are weeds that are generally established in scattered populations in some counties of the State. Such weeds are subject to:

Active exclusion where possible.
Active eradication from the premises of a dealer of nursery stock.

Category C weeds are weeds that are generally established and generally widespread in many counties of the State.

Category A Noxious Weeds
	*Black henbane (Hyoscyamus niger)* Annual or biennial. Grows up to 3 feet tall in disturbed areas including roadsides and pastures. The greenish-yellow flowers have a purple center with 5 fused petals. This species is toxic to livestock. Flowering occurs from May to August. It reproduces by seed.
	*Dyer’s woad (Isatis tinctoria)* Biennial, occasionally an annual or short-lived perennial. Grows up to 3 feet tall. It may form dense colonies in disturbed roadsides, pastures and rangeland. The bright yellow flowers occur in corymb like racemes. Flowering occurs from April to June. It reproduces by seed.
	*Houndstongue (Cynoglossum officinale)* Biennial, rarely an annual or perennial. It grows from 1 to 3 feet tall in disturbed areas including roadsides, pastures and fence lines. The purple to pink flowers have five petals. This species is toxic to livestock. Flowering occurs from May to September. It reproduces by seed.
	*Mayweed (Anthemis cotula)* Annual. Grows 1 to 2 feet tall. Invades disturbed areas. The disc flowers are yellow and the ray flowers surrounding the disc are white. The plant has a very strong odor and is referred to as “stinking chamomile”. Flowering occurs in spring and summer. Reproduction occurs by seed only.
	*Mediterranean sage (Salvia aethiopis)* Biennial. Grows up to 3 feet tall and is commonly found in degraded sagebrush habitat. The white to yellow labiate flowers are arranged in clusters along the stem. Flowering occurs from June to August. This plant reproduces by seed.
	*Purple loosestrife (Lythrum salicaria)* Perennial. Grows between 3 and 6 feet tall and forms dense colonies in riparian and wetland habitats. Once established it is difficult to control. The bright purple flowers occur in long spikes or racemes at the end of a stem. Each plant can produce up to 3 million seeds. Flowering occurs from July to September. It reproduces by seed and rhizomes.
	*Spotted knapweed (Centaurea biebersteinii)* Biennial. Grows up to 4 feet tall by the second year. It may form dense colonies, commonly in rangelands. The flowers range from white to purple and occur at the end of long branches. In its first year this species only grows a rosette of pinnately divided leaves. This species is allelopathic, suppressing the growth of other plants. Flowering occurs from June to October. It reproduces by seed and lateral roots.
	*Yellow starthistle (Centuarea solistitialis)* Annual, rarely a short-lived perennial. Grows from ½ to 6 feet tall. It forms dense colonies and is extremely competitive. The flowers are yellow and subtended by long very sharp spines. This species is toxic to horses and can cause chewing disease. Flowering occurs from July to August. It reproduces primarily by seed. Seed can remain dormant in the soil for up to 10 years.
Category B Noxious Weeds
	Leafy spurge (Euphorbia esula) Perennial. Grows up to 3 feet tall. The root system is very deep, up to 14 feet, making it difficult to control once established. It may form dense colonies. The flowers are yellow-green clusters at the end of branches. Beneath the flower is a pair of heart shaped yellow-green bracts. The entire plant contains a milky juice. Flowering occurs late spring to fall. Reproduction occurs by rootstock and by exploding seed capsules, capable of throwing the seed up to 30 feet.
	*Medusahead (Taeniatherum caput-medusae)* Annual grass. Grows from ½ to 2 feet tall in rangelands across the western United States. Medusahead contains large amounts of silica and the florets have long awns which make it unpalatable to livestock and othe r herbivores. This plant reproduces by seed.
	*Musk thistle (Carduus nutans)* Biennial thistle. Grows from 2 to 6 feet tall in disturbed roadsides, pastures and riparian areas. Flower heads can be up to 3 inches across and contain bright pink to purple flowers. Leaves have a light green midrib. Flowering occurs from July through September. This species reproduces by seed.
	*Russian Knapweed (Acroptilon repens)* Perennial. Grows from 1.5 to 3 feet tall. Forms dense colonies. Black roots penetrate to over 8 feet deep. The flower is usually pink in lavender in color and forms on the end of a cone shaped head. The bracts on the flower are papery which differentiates it from the other knapweeds. Flowering occurs between June and September. Reproduction occurs from seed and rhizomatous root system.
	*Scotch thistle (Onopordum acanthium)* Biennial. Forms a rosette the first year and flowering stems elongate the second year. The plant grows up to 12 feet tall. The stems have broad, spiny wings. Basal leaves may be 2 feet long and 1 foot wide. Solitary purple flowers are at the end of the branches. Reproduction is by seed only.
Category C Noxious Weeds
	*Canada thistle (Cirsium arvense)* Perennial. Grows from 1 to 4 feet tall. Forms dense colonies with deep extensive rhizomatous root systems. Flowers are light lavender to deep rose purple in color and are either male or female, which differentiates it from true thistles. Flowering occurs during July and August. Reproduction is by seed or rootstock.
	*Hoary cress (Cardaria draba)* Perennial. Grows 1 to 2 feet tall. It may form dense colonies and often invades disturbed areas. The flowers are white with four petals and occur in a dense cluster at the end of stems. The leaves clasp around the upper stem and are blue-green. Seed pods contain two seeds and are heart-shaped. Flowering occurs from May to June. Reproduction occurs by seed and creeping rhizomes.
	*Perennial pepperweed (Lepidium latifolium)* Perennial. Grows from 1 to 3 feet tall. Forms dense colonies. It has a dense, deep root system which make it difficult to control. White flowers form dense clusters near branch ends. Flowering occurs between June and September. Reproduction occurs by seed and rootstocks.
	*Poison hemlock (Conium maculatum)* Biennial. Grows up to 8 feet tall. It forms dense colonies, commonly near streams. The white flowers occur in large umbels that are 4 to 6 inches across. This species contains eight different alkaloids some are very toxic to humans and livestock. Flowering occurs from June to August. It reproduces primarily by seed.
	*Puncturevine (Tribulus terrestris)* Annual. Prostrate branches grow up to 3 feet long in disturbed roadsides. Yellow flowers with 5 petals bloom from June to September. The leaves can be toxic to livestock and seeds can cause damage to tires. This plant reproduces by seed. Fruits have 5 nutlets, each with 2 thick spines.
	*Salt cedar/tamarisk (Tamarix ramosissima)* Deciduous shrub or small tree growing 5 to 20 feet tall. Few plants grow under its canopy because high concentrations of salt from the leaves accumulate on the ground beneath the plant. Pink to white flowers bloom from spring through summer. Leaves are scale-like, on highly branched slender stems. The bark is reddish brown and fissures with age. This plant has an aggressive root system and monopolizes water sources. Reproduction is by seed. A single tamarisk tree can use up to 200 gallons of water per day and can drastically alter riparian areas.