Bear Lodge Project – Bull Hill Mine
January 2013
Weed Management Plan
8
Scotch thistle is a biennial, or sometimes annual, that grows erect up to 8 feet tall, reproducing only
by seed. Rosette forms the first year with a flowering stem forming the second year. Leaves are
large and coarsely lobed with hair on both sides giving them a velvety-grey appearance. Basal
leaves can be 2 feet in length and 1 foot wide. Leaf margins are lined with sharp spines. Flowers
are solitary, 1 to 2 inches in diameter, and violet to reddish in color. Bracts on the flower are spine-
tipped. The root is a large fleshy taproot. Seeds are dark brown to black in color, distinctly
wrinkled, and 3/16 of an inch long.
Management Objective
: Containment
Integrated Management
Chemical: Clopyralid, dicamba + difluferzopyr, clopyralid + 2,4-D, aminopyralid,
metsulfuron, picloram, and chlorsulfuron are all effective control agents on rosette
stage.
Biological: There are no known biocontrol agents approved for use.
Cultural: Increased competition from desirable plants and proper management of perennial
grasses is effective.
Manual/Mechanical: Digging and pulling is effective when most of the tap root is removed.
Mowing can be successful once stems are elongated and bloom has started.
Russian knapweed
Spotted knapweed is a biennial or short-lived perennial that grows up to 3 feet tall and spreads by
seed. Rosette formed the first year with a flowering stalk elongating the second year. Stems are
erect with slender wiry bracts and are covered with fine hair. Flowering heads are mostly on branch
tips, solitary, up to one inch in diameter, and pink to purple in color, rarely white, with black tipped
seed head bracts. Leaves are long and divided below the branches and short and narrow above;
covered with fine hairs. Seeds are brownish, 1/8 inch long, notched on one side of the base, and
have short tufts of bristles at the tip.
Management Objective
: Containment
Integrated Management
Chemical: Imazapic, aminopyralid, glyphosate, picloram, clopyralid, clopyralid + 2,4-D,
clopyralid + triclopyr, and chlorsulfuron are all effective control agents.
Biological: Banded knapweed gall fly (
Urphaora affinis
), UV knapweed seedhead fly
(
Urophora quadrifasciata
), green knapweed clearwing fly (
Terellia virens
),
knapweed peacock fly (
Chaetoreellia acrolophi
), knapweed seedhead moth
(
Metzneria paucipunctella
), lesser knapweed flower weevil (
Larinus minutes
),
blunt knapweed flower weevil (
Larinus obtusus
), broad-nosed knapweed
seedhead weevil (
Bangasternus fausti
), sulphur knapweed root moth (
Agapeta
zoegana
), brown-winged knapweed root moth (
Pterolonche inspersa
), gray-
winged knapweed root moth (
Pelochrista medullana
), knapweed root weevil
(
Cyphocleonus achates
), and bronze knapweed root borer (
Sphenoptera
