Like its cousin kochia, Russian thistle is an annual weed that is highly adaptable to hot, dry conditions. It grows rapidly with its red-striped stems growing over one metre high with its extensive root system reaching almost two metres down.
The leaves are alternate, long, 2-5 cm (about 1.97 in), narrow, dark green, and fleshy. The later leaves are shorter, broader, and are tipped with stiff spines.
The flowers are small, 2 mm (about 0.08 in) wide, green or pinkish, inconspicuous, and occur in the axils of upper leaves. Two spiny-tipped bracts, which is a small, modified leaf, accompany each flower. The seeds are a cone shaped coiled utricle, 2 mm (about 0.08 in) in diameter, dull brown to grey in colour. Just one mature plant can produce 200,000 seeds and when high winds break the brittle stems, it becomes a tumbleweed, scattering seeds far and wide.
Group 2 resistance
As with kochia, Russian thistle is also known be resistant to Group 2 (ALS inhibitor) herbicides in Alberta and Saskatchewan. A Manitoba survey of Russian thistle populations collected in 2018 found that the Russian thistle did not exhibit resistance to herbicide groups 2, 4 or 9 (glyphosate). However, according to the Canadian Journal of Plant Science, there have been recent confirmations of glyphosate-resistant populations found in Montana, Washington and Oregon.
Diverse cultural practices
Researchers recommend cultural practices that focus on achieving canopy closure so the crop can use the available space to intercept sunlight and other resources, so they are unavailable to weeds like Russian thistle and kochia. Other practices include increased seeding rates, narrow row spacing and crop rotations.
Multiple modes of action
Multiple, effective modes of action on Russian thistle should be incorporated into management strategies through layering, tank-mixing, sequential applications, and rotating between years. Using different modes of action will kill the weed in separate ways, making it more challenging to overcome any one herbicide.
A pre-seed burnoff using Intruvix™ II herbicide will help control the weed before it becomes competitive with the crop. Intruvix™ II herbicide delivers fast-acting, systemic action of over 50 emerging broadleaf weeds including Russian thistle. When tank-mixed with glyphosate, Intruvix™ II herbicide uses four modes of action to help prevent resistant weed escapes.
And spring wheat, durum, barley or oats can be seeded 24 hours after application. When you apply Intruvix™ II herbicide for spring burnoff or chemfallow, you have wide-open re-cropping flexibility next spring.
Suitable for all soil types from brown to black to grey, the all-in-one formulation of Intruvix™ II herbicide provides quick and lasting burnoff control of tough weeds like Russian thistle, kochia, narrow-leaved hawk’s-beard and volunteer canola in front of cereals.
Sources:
https://www.gov.mb.ca/agriculture/crops/weeds/russian-thistle.html
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