Russian Thistle (Tumbleweed)
Russian thistle, commonly known as tumbleweed, is a member of the goosefoot family (Chenopodiaceae).
Russian thistle is categorized as a Summer Annual. It first came to the US as a weed seed transported to South Dakota in flax imported from Russia. From there, it spread via railroad cars, wind, and other transports. It’s now a common and invasive weed across the western United States, infesting over 100 million acres of land. The species thrives in regions with summer drought and winter rains. California is one of its favorite states, but it’s found at varying levels of regularity across the West.
Russian thistle can be found anywhere the soil has been disturbed--across vacant lots, along highways and fence lines, and in other non-crop areas. In turf crops where the soil is tilled or mowed often, it will rarely become significant.
Russian Thistle Identification
Russian thistle is a bushy weed, with a number of slender stems which gain turgor and develop into a woody type texture at maturity. They’ll vary in length from 6-36”. When vegetative, the stems will exhibit reddish or purple stripes.
The plant’s seedlings actually develop as plantlets inside the seed. Under optimum moisture and a wide temperature range between 50-90 degrees, the plantlet uncoils, and its taproot develops in the soil. This type of development lends itself to rapid germination, sometimes less than 12 hours. It will canopy over competing weeds and plants very effectively. One Russian Thistle can release more than 200,000 seed over several miles.
When germinating, the seedlings resemble pine needles they are so fine. When small and succulent, Russian thistle’s dark green, fleshy leaves could be grazed or foraged as their leaves are fleshy and short, only 1” in length typically. Similar to Kochia; Russian Thistle can be toxic to animals, particularly cattle and sheep. The vegetative stage can accumulate excessive nitrate levels in the leaves, and when ingested as too much of the diet, can cause respiratory problems, and even sudden death in these ruminants. The other way they can be poisonous is due to their higher than normal percentage of oxalates, which can shut down kidney function of ruminants.
Once they mature and become more coarse and woody, the older leaves develop a sharp-point to the tip; discouraging animals from eating them. They can grow to be more than 6’ wide under favorable conditions. Their flowers are inconspicuous and occur as bracts, without any distinguishable petal; also very pointed and undesirable to predators. The brittleness of the ‘bush’ once mature and seed has been set, will cause the above ground portion to break off in fall and early winter. As these round, spiny plants travel across the plains or flat lands, seed is dispersed as the weeds ‘tumble’ across vast open areas.
Come spring, many months after the seeds are deposited, it’s not uncommon to see trails of tiny Russian Thistle following a directional pattern similar to the tractor while plowing… this results from the seeds being trapped between the furrows as the tumbling weed was blown across the field. This should not be taken lightly as they will quickly establish in these ‘trails’.
Russian Thistle as an Economic Pest
Russian thistle is a very competitive weed when not kept in check. It will rob water, light, nutrients, yield, and quality. The first little seedlings will be the most competitive. Therefore, any escapes should be controlled before they are 3” tall. When severe, the weed can delay grain harvest because of their high moisture content, raising the average moisture content above threshold for the harvested crop. In severe cases, the crops can become unharvestable.
Russian Thistle Management and Control
In agronomic crops (small grains, corn, cotton, soybeans, etc), the overall objective for managing Russian Thistle is preventing seed production by the weed. Pre-emergent herbicides or other activities to prevent its germination are the most effective means of preventing economic populations.
Post emergent control should be done when the weeds are very small. If you have heavy populations visible in the field in the crop nearing harvest, pre-harvest applications may be advisable to speed dry down. Post harvest control should be done soon after harvest. In certain areas, fall tillage can reduce residues and dry out soils; so applying labelled herbicides may be advisable to retain residues into the winter in dry climates.
Of utmost importance is to not plant into a live stand of Russian Thistle, regardless of its height. Burn it down, till it up, tank mix burndown with pre-emergent materials; whatever it takes; but do not plant into a live stand.
Russian thistle is a known resistant biotype to ALS inhibiting herbicides. Suspected Triazine Resistant Russian Thistle is also under review. Kansas State University has identified Russian Thistle as being resistant to glyphosate, as well.
An integration of Best Management Practices (BMP’s) involving rotation, competition, scouting, and proactive management come together to provide you with the best approach to controlling Russian Thistle.
Consult with your local Certified Crop Advisor or Specialist in your region for labelled and recommended crop protection materials, timing of application, and cultural practices best implemented in your particular area.