Noxious weeds and how to kill them

Sean Gephart from the Nevada Department of Agriculture (DOA) recently updated the Humboldt County Commissioners about efforts to control or kill noxious weeds.

The DOA identifies weeds as noxious when they are hard to control or problematic, or when they impact wildlife habitat or agricultural yields. Noxious weeds can also become a significant fire hazard.

Gephart listed six noxious weeds found in the Paradise Valley Weed Control District. 

Medusahead looks like cheatgrass, with a long, slender stalk and bristly head, but with longer, needle-like segments. Animals can’t eat it, and when this annual grass dies, it creates a thick mat that is difficult to destroy and poses a significant fire hazard. The best method of control is burning it, removing the thatch material then applying herbicide to the soil. Reseed in the fall.

Russian knapweed has been found throughout the state. It has a purple flower similar to a thistle. It is toxic to horses and can cause a chewing disease that may lead to dehydration and starvation. Gephart warned that tilling Russian knapweed only spreads it because the plant can grow from the roots as well as seeds. Apply herbicide once the plant goes dormant in late summer.

Yellow starthistle has only been found in one place in Humboldt County, though it has become more of a significant problem along Interstate 80 near Reno and in Douglas County. It has become unmanageable in California. 

The yellow flower heads have long thorns, making the plant difficult to remove by hand. The root system also makes it difficult to remove. Gephart advised removing the plant and roots before it goes to seed, then treating area with herbicide. It has a staggered germination cycle, and might require more than one treatment over a few weeks to clear it out.

Perennial Pepperweed has become a significant issue in Paradise Valley. The “bulbous, succulent” roots cause soil erosion along waterways. When it dies, the stalks become woody, and impact water fowl habitat. Like Russian Knapweed, the plants can grow from root matter, so tilling only spreads it. Gephart said to use a herbicide approved for aquatic weeds if near water.

Leafy Spurge is a perennial and can grow from seeds or roots. It’s very adaptable, growing along waterways and wastes. After the first significant frost, look for white, milky sap in the weed material. That’s the best time to spray herbicide to kill it.

Scotch Thistle can grow to a “12 foot tall impenetrable mass,” according to Gephart. He suggested removing the whole plant before it goes to seed. Musk Thistle is the same.

Landowners are required to control noxious weeds on their property. The county should be notified if any landowner fails to do so. If the county needs to intervene in order to prevent the weeds from spreading, it may choose to put a lien on the property.