Cooperative Extension educator JoAnne Skelly knows her enemy.
Growing in abandoned fields and along ditches in Carson City, the invaders push out native species, promote erosion and generally take over the place.
They are not unattractive, but allowed to spread, they could alter the Western Nevada landscape significantly.
Skelly is a scout in the battle against noxious weeds, spotting them, identifying them and then calling in the artillery.
"We're seeing so many weeds," she said during a short tour of Carson City's empty spots.
"One of the things we tell people is not to drive through contaminated areas," she said as she brushed seeds from her shoes after tromping through a patch of Russian knapweed.
The perennial is spreading across the field north of Glen Eagles. Its purple flowers can produce lots of seeds.
It is listed as a noxious weed by the Nevada Division of Agriculture.
She found a small stand of spotted knapweed along the Andersen Field across from Carson-Tahoe Hospital.
The weed was in Mountain Street's right-of-way. Unlike its cousin, spotted knapweed is a biennial and is one of the leading problem weeds in the United States.
Skelly says knowing the weeds' life cycle is critical to fighting them.
Russian knapweed can be eradicated using chemicals, but that wouldn't do any good against the spotted knapweed in its second year.
"You can spray Russian knapweed but if you don't get the spotted knapweed before it goes to seed, your not stopping it," she said.
Mowing the biennial in the second year and then spraying those plants in their first could do the trick.
Not all weeds are classified as noxious. Many a Nevadan has struggled with Russian thistle, otherwise known as tumbleweed, but it is not considered a noxious weed.
"Noxious weeds can really over take the native plants and destroy habitat," Skelly said.
One famous noxious weed, tall whitetop, does not provide erosion control and replaces those native plants that do.
If unchecked, noxious weeds can get into hay fields and reduce or destroy the value of the hay.
Worse, eating yellow star thistle,can cause a neurological affliction among livestock called chewing disease.
According to a Cooperative Extension fact sheet, large infestations of yellow star thistle have been found in Carson City, Douglas and Washoe counties.
In Nevada it is the responsibility of the landowner to deal with noxious weeds.
Skelly's job is educating people to the dangers and identifying the weeds. She turns over what she finds to the agriculture division, which notifies property owners.
Carson City does not have a weed control district.
She says noxious weed seeds can come in from many sources including fill dirt and straw bales.
For the uneducated gardener noxious weeds are sometimes hard to spot, Skelly says.
"If people are confused, bring a sample by the office and I'll identify it," she said.
Russian knapweed -- Up to 3 feet tall with semi-erect stems and blue-green leaves. Showy cone-shaped flowers can be white to purple in color.
Spotted knapweed -- Up to 4 feet tall in second year. Starts as a rosette of small leaves close to the ground in the first year. Flowers are pink to purple, solitary and up to one inch in diameter.
For information: Call Cooperative Extension at 887-2252. You can e-mail JoAnne Skelly at Skellyj@unce.unr.edu. The extension's Web site is www.nce.unr.edu