Hoary alyssum (Barter incana) is spreading aggressively in Ferry County, says Dan Fagerlie, Washington State University Extension agent for Ferry County.
     The new invader, which was put on the 2004 state noxious weed list, can be found just starting along driveways and rangeland roads, according to an extension announcement.
     "It blooms all through the summer with its white flowers, but the time to control it is now in the seedling stage using a selective spray or hand digging," according to the announcement. "Having a healthy grass stand slows the spread."
     Hoary alyssum is in the mustard family and grows aggressively along roadways, pastures and on rangelands. It prefers dry, sandy or gravely soils but can spread very rapidly in most soils, according to the announcement.
     In Ferry County control is mandatory in the southern weed district No. 5 and along vehicle corridors elsewhere because it spreads so fast. It can be toxic to horses if they consume a substantial amount as a portion of their diet, according to the announcement.
     It usually grows one to three feet tall with erect stems branching near the top. The stem leaves and seed pods are covered with whitish-gray short hairs, which give the plant a pale light green color, according to the extension office. It is an annual to short-lived perennial with alternate leaves that are simple, smooth-edged and narrowly oblong.
     Clusters of flowers at the tip are white, conspicuous in a raceme, which produces seed and keeps blooming at the tip as it grows out continually producing more seeds. It has four deeply divided small, white petals.
     Hoary alyssum flowers from June to fall and mature seeds form from July to October. It has a non-rhizomanous root system and reproduces by seeds.
     "You can vigilantly hand-pull small infestations, especially if near flowering," according to the announcement. "Selective herbicide treatments may be used. It is completely resistant to piclorum (Tordan) but susceptible to many selective herbicides."
     The extension office advises pulling or digging plants before seeds drop to control spread by seed. Herbicide treatments should be done in the spring before the plant begins to bolt up and flower, according to the announcement.
     A summer or fall herbicide treatment also may be applied to stop seed production. Repeated treatment through the year may be needed in most sites, say extension officials.
     Plants can be found in any part of the county but the largest infestations are in the Curlew and Malo areas.
     People who suspect they have hoary alyssum or other noxious weeds can bring them to the extension office in Republic for identification, according to the announcement.
     Control assistance information is available from the Ferry County Noxious Weed Control Board office, 775-5210. Control assistance is available this year while funds last, according to the announcement.