Written by: Alyson Buchanan, Colorado Master Gardener Apprentice

Kochia (Kochia scoparia) and Russian thistle (Salsola trigus) are two non-native species of weeds that become tumbleweeds.  Both are summer annual broadleaf weeds that thrive in areas where the soil has been disturbed, such as along ditches and roadsides, in construction areas, cultivated fields, or yards with little vegetation. These plants reproduce from seed, which germinate from spring through summer.  Each plant can produce hundreds of thousands of seeds that will be spread far and wide across our southern Colorado landscape as the plants dry out and become tumbleweeds, tumbling along with the fall and winter winds.  Tumbleweed management can be achieved through preventing seed germination, preventing seed production, and depleting the seed bank.

Kochia form pyramidal or conical shaped bushes 6 feet tall or more.  Seeds germinate in early spring, sending down a shallow taproot.  Seedlings have alternate gray-green leaves with hairy undersides and margins with lower leaves often wider than upper leaves.   Stems grow 1 to 6 feet tall, are highly branched, green or red tinged with inconspicuous yellow flowers.  Seed production occurs from July through October.  In fall, the entire plant becomes reddish-brown, then brown, at which time the stems break off at the base with the plant becoming a tumbleweed.

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Russian thistle form large oval to round shaped prickly bushes with numerous slender ascending stems that become woody and grow to 6 feet or more in diameter. Seeds germinate in loose soil during late winter or early spring, taking advantage of winter moisture to send down a deep taproot.  Seedlings are dark green, fleshy and look like pine needles or grass seedlings. Later, leaves become short and spiny, growing on brittle stems that have red or purple striations with alternate branches.  Flowers are green and very inconspicuous, accompanied by a pair of spiny, floral bracts.  Seed production occurs from July through October.  In fall, the entire plant becomes brown, at which time the base of the stem becomes brittle and breaks off at the base with the plant becoming a tumbleweed.

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Tumbleweed Management requires a multi-pronged approach that includes cultural, mechanical, and chemical control methods.  Kochia and Russian thistle seeds have a short viability of 2-3 years, so when tumbleweeds are consistently managed for 2-3 years using these methods, where no seed production occurs, local eradication can result.

Cultural Methods include:

• Mulching at appropriate levels of 3-4 inches to prevent seeds from germinating in the sunlight.
• Limiting soil disturbances from equipment, animal, and human foot traffic to prevent loosening soil and spreading seeds.
• Planting competitive, more desirable species such as grasses. Manage the more desirable species until it has fully established a competitive advantage. Grasses are very competitive and allow for selective weed management methods like mowing or specific herbicides, e.g., 2,4-D, that do not harm grasses.
• Removing tumbleweeds from fence lines and around other plants and trees to keep seeds from continuing to spread and adding to the seed bank.

Mechanical Methods include:

• Mowing young plants when they are beginning to bloom to prevent seed production can be a limited option, as seeds can still be produced on branches below mowing levels.
• Hand pulling, hoeing or any method that disrupts contact between the plant roots and soil are effective at controlling both seedlings and larger plants. If plants have begun producing seed, they should be collected and disposed of to keep seeds from contributing to the seed bank.

Chemical Methods include:

• Utilizing a combination of pre-emergent and post-emergent herbicides for the best results. Note: Be sure to read the label, follow all instructions, wear personal protective equipment such as shoes, long pants, etc., it is the law.
  • Pre-emergent herbicides should be applied to the soil beginning in late winter through summer before the weed seed germinate (pre-emergent herbicides will not kill growing weeds) and should usually be incorporated into the soil with snowfall, rainfall or irrigation, where the herbicide will remain active in the soil for weeks to months. Examples of effective pre-emergent herbicides include trifluralin (Preen, Treflan), pendimethalin (Prowl, Pendulum), oryzalin (Surflan).
  • Post-emergent herbicides should be applied to growing plants, but timing is critical. For best results, these herbicides should be applied when the weed is in its early growth stages, before it becomes hardened and starts producing its spiny branches. Post-emergent herbicides will remain active for days, but if rain or irrigation occur after application, additional seedlings may emerge and require future applications.  Examples of effective post-emergent herbicides include fluroxypyr (Vista, Starane), 2,4-D (many brand names) is effective for Russian thistle, but not Kochia, dicamba (Roundup, Banvil, Clarity), glyphosate (many brand names). 2,4-D and dicamba are selective herbicides that will control many broadleaf weeds but usually do not injure grasses.

In summary, consistent tumbleweed management that includes a combination of cultural, mechanical and chemical control methods over a 2-3 year period will enable you to make a significant impact in preventing seed production, preventing germination, and depleting the seed bank of Kochia and Russian thistle.  Local tumbleweed eradication is possible!

References

Colorado State University Extension, Fact Sheet No. 6.314, Identification and Management of Kochia and Russian Thistle, https://extension.colostate.edu/topic-areas/natural-resources/identification-and-management-of-kochia-and-russian-thistle-6-314/

Colorado State University Extension, Plant Talk 2124 – Kochia and Russian thistle, https://planttalk.colostate.edu/topics/weeds-cultural-problems/2124-kochia-russian-thistle/

Colorado State University Extension, Colorado Master Gardener Notes #351, Weed Management, https://cmg.extension.colostate.edu/Gardennotes/351.pdf

University of California Cooperative Extension, Publication 7486, Russian Thistle, https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnrussianthistle.pdf

New Mexico State University, Management and restoration of areas infested with Russian thistle and Kochia in southern New Mexico, https://weeds.nmsu.edu/pdfs/Russian_thistle_and_kochia_homeowner.pdf