INVASIVE PLANTS - Technical Learning College

Russian thistle was introduced from Russia and is an annual which reproduces by seed. It is a
round, bushy, much-branched plant, growing 1 to 3-1/2 feet high. The branches are slender,
succulent when young, and woody when mature. Russian thistle grows on dry plains, in
cultivated fields, roadsides, and waste places, chiefly in grain-growing areas. At maturity, the
plant breaks off at the base and because of its round shape, becomes an excellent
tumbleweed. Russian thistle is an annual. A single plant may produce 20,000 to 50,000 seeds.
Seeds germinate quickly, even after brief or limited precipitation. The plants are well branched,
round bushy that grow 1/2 to 3 feet high. The stems have reddish or purple strips. The leaves are
alternate, long, and very thin or needle-like. Flowers are small and inconspicuous and develop in
the upper leaf axils. Each flower has a pair of spiny bracts. Mature plants break off at ground level
and tumble, spreading the seeds. This species is a host of sugar beet leafhopper, which transmits
curly top of sugar beets. This weed is common in drier areas and in dry land cultivation systems.
It is found in overgrazed rangeland, disturbed waste areas and in wheat, sugar beet, potato, and
mint crops east of the Cascade Mountains.
Control Control of Russian thistle is difficult. There have been numerous attempts through the years
to import biological control agents, but none have been successful.
Pre-emergent herbicides are applied to the soil before the weed seed germinates and are
usually incorporated into the soil with irrigation or rainfall. The most effective pre-emergent
herbicides are Aatrex (atrazine), Velpar (hexazinone), Devrinol (napropamide), Telar
(chlorsulfuron), Oust (sulfometuron), Princep (simazine) and Hyvar (bromacil). Other preemergent
herbicides that are registered but only moderately effective in controlling Russian thistle
are Surflan (oryzalin), Treflan (trifluralin), Prowl (pendimethalin), Endurance (prodiamine), Lasso
(alachlor), Predict (norflurazon), and Kerb (pronamide).
Herbicide-resistant biotypes of Russian thistle have evolved in only a couple of years following
treatment with Telar (chlorsulfuron) or Oust (sulfometuron). Avoid repeated use of a single
herbicide or of herbicides that have the same mode of action to prevent the evolution of
herbicide-resistant populations.
Post-emergent herbicides are applied to plants, but timing is critical. For best results, these
herbicides must be applied while the weed is in its early growth stages, preferably the early
seedling stage, before it becomes hardened and starts producing its spiney branches. Do not use
post-emergent herbicides to try to control the mature seed (either on the plant or on the ground)
as they are not effective for this purpose. Also, the later spiney stage of Russian thistle is not
readily controlled by any post-emergent herbicide. If rain or irrigation occurs after a postemergent
application, additional seedlings may emerge and require future treatments. Postemergent
herbicides that are effective when properly applied include Banvel or Vanquish
(dicamba), Roundup (glyphosate), 2,4-D and Gramoxone (paraquat).
Milkweed plants, members of the Asclepias family, are the only host plant for the monarch and
queen butterflies. The adult females seek out these plants on which they lay their eggs. The
caterpillars that hatch will remain on the plants and eat the leaves until they enter the pupal stage,
then emerge as adult butterflies. It is a perennial herb with long-spreading rhizomes. Stems are
stout, erect, to 2 m tall, with short downy hairs and milky juice; leaves opposite, oblong, rounded,
1–2.6 dm long, 0.4–1.8 dm broad, with prominent veins; upper surface smooth, lower covered
with short white hairs and strong transverse nerves. Flowers sweet-smelling, pink to white, in
large, many-flowered, axillary and apical bell-like clusters; corolla lobes 6–9 mm long, hoods 3–4
mm high; follicle grayish, hairy, with soft spiny projections, 1–3 mm high, slenderly ovoid, 2.5– 3.5
cm thick. Seed brown, flat, oval, 6 mm long, 5 mm wide, with a tuft of silky white hairs apically
(Reed, 1970)
Control Non-Cropland -- Established stands of common milkweed can be controlled with
herbicides. On non-cropland (i.e., roadsides, railroad rights-of-way, etc., but not idle land or
grazing land), Amitrol-T, Roundup or Tordon would provide control. Herbicide coverage of the
common milkweed is incomplete with this method, resulting in reduced effectiveness compared to
a sprayer. Used over several years, however, common milkweed populations can be reduced
with Roundup applied in a wiper applicator. Controls: Amino Trizole; Amitrol-T, Roundup, 2,4-
D+Banvel,and Tordon
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