Understand Russian Thistle to Manage Resistance

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Russian thistle is a bushy, noxious annual weed that is often called tumbleweed. It occurs throughout the western states, more often in drier areas. (photo courtesy of Andrey Zharkikh)

Russian thistle (Salsola tragus) is commonly called tumbleweed. It is primarily found in fields where the soil has been disturbed, as well as along fencelines, ditches, pastures and untended landscapes. It is particularly well-adapted to cultivated, dryland field crops such as wheat, other cereals, corn, soybeans and cotton. Russian thistle is common in the western United States, but may be found in many other states.


Identifying Russian Thistle

Russian thistle is a bushy summer annual weed with thin, upward-growing stems that become woody when mature. Seedlings have finely dissected leaves that are about 1 inch long, narrow and a dark green color. Russian thistle seedlings look similar to pine seedlings. As weeds mature, their stems can grow up to 3 feet tall and have red or purple stripes. The roots of a mature Russian thistle plant can grow up to 6 feet deep and 6 feet wide.

Flowers are subtle and develop in the axils of the upper leaves. A pair of spiny, floral bracts accompanies each flower. Each small, one-seeded fruit has winged tips. Russian thistle can emerge throughout the growing season. Typically, seeds germinate in late winter or early spring and usually emerge in early April through late June. Plants typically flower from July through October.


Favorable Conditions for Prolific Weed Seed Production

Russian thistle develops as a small plantlet inside the seed. Under conditions of ideal moisture and temperatures of 52 to 90 degrees, the plantlet begins to uncoil. A young taproot develops in the soil, allowing germination to occur in 12 hours or less, giving Russian thistle a significant advantage over many other plants competing for limited moisture.

One Russian thistle plant can produce approximately 250,000 seeds. After seed maturation, which generally occurs from August through October, the plant stem detaches from the root. The plant is then carried by wind, scattering seeds as it tumbles across fields and other landscapes, similar to kochia.

In spring, months after seeds are deposited into the soil, farmers may see green trails of germinating Russian thistle seedlings resulting from the paths taken by tumbleweeds blown across plowed fields. This requires additional control measures to protect yields.


Potential Damage and Economic Impact

Russian thistle competes with crops throughout the growing season, robbing them of water, sunlight, nutrients and yields. Yield loss increases with density of Russian thistle populations. The first Russian thistles to emerge will be the most competitive, so it’s important to control weeds early before they reach 3-inches-tall.

Another worry for farmers is that Russian thistle can delay grain harvest because of the weed’s high moisture content in the field. It can also increase grain moisture levels because of weed particles mixed with grain after harvest. In some cases, fields have become unharvestable because of moderate to high densities of Russian thistle.


Known Resistance in Russian Thistle

Russian thistle is resistant to ALS-inhibiting herbicides (Group 2). Resistance to triazines (Group 5) is also suspected. Another concern for farmers to consider is that Russian thistle is among a list of weeds posing the greatest concern for glyphosate (Group 9) resistance, according to Kansas State University.

It’s sometimes a challenge for farmers to keep track of the many factors that contribute to the management and proliferation of herbicide-resistant weeds; therefore, the best approach to manage resistance is to use best management practices (BMPs) to keep tough-to-control and resistant weeds from going to seed and entering the soil seedbank, where they can remain viable and cause problems in future crops.

For more information on Russian thistle and other confirmed resistant weeds by state, refer to the International Survey of Herbicide Resistant Weeds.


Russian Thistle Control

The most effective management strategies for Russian thistle in cereals, corn, soybeans and cotton should focus on preventing seed production throughout the year. Russian thistle is most susceptible to herbicide application prior to emergence and before weeds exceed 2 to 3 inches in height. The first weeds to emerge will be the most competitive and difficult to control.

  • Consider pre- and postharvest spraying where dense populations of Russian thistle exist in your field. Farmers benefit from a preharvest application because it helps speed dry-down of Russian thistle, improves harvest efficiency and lessens residue difficulties during fall cultivation. At postharvest, control Russian thistle with appropriate herbicides or with tillage two weeks after harvest. Tillage eliminates most Russian thistle but will result in less residue and less water/soil moisture retained in the soil through winter than the use of postharvest herbicide control.
  • Do not plant into existing stands of Russian thistle. Start weed-free at planting using a burndown tankmixed with a pre-emergence residual herbicide just prior to or at planting.
  • Russian thistle-infested fields not treated with a fall herbicide application or not cultivated in the fall can result in early-emerging weeds in the spring. In these situations, Russian thistle should be controlled early to ensure effective burndown. Farmers may want to apply burndown herbicides with some of the residual herbicide in early spring and then apply the remainder of the residual herbicide at planting. Remember to manage resistance by choosing products with different modes of actions from different classes of chemistry.
  • Crop competitiveness and crop rotation are two important cultural practices in cereal, corn and soybean crops. Managing crop residue, controlling weeds and planting high-quality, uninfested seed helps establish a vigorous crop to compete more effectively with emerging weeds for water, light, space and nutrients. Depending upon geography, farmers may consider rotating grain crops such as corn, grain sorghum, wheat, soybeans and sunflower.

Bayer Solutions

Crop Science has a broad portfolio to combat tough-to-control and resistant weeds. A well-thought-out herbicide program, using multiple modes of action, should be implemented to sustainably manage weeds. Before applying any herbicide, please read the entire label for the best possible results and to confirm that the product is effective on the weeds you wish to control. Not every product is suitable for every situation, and use of the correct application technique will ensure the best results.

The following Bayer solutions are valuable tools to consider for your program.

Corn Solutions for Russian Thistle Management

When managing corn crops for high yields, remember it’s always best to start with a clean field. Start with an Autumn™ Super (2) application in the fall, and the following spring use Corvus® (2, 27), as a pre-emergence residual herbicide which has overlapping modes of action to control early season problem weeds. Corvus pre-emergence herbicide from Bayer is the only corn herbicide to offer burndown, residual and reactivation. Residual activity prevents new weeds, while reactivation controls late weeds.

The multiple modes of action in Corvus deliver consistent, broad-spectrum control of grasses and broadleaf weeds, including weeds resistant to glyphosate-, ALS-, PPO- and triazine-based herbicides.

A wide application window allows for application from pre-plant to early postemergence at V2, making it an effective, long-lasting first pass herbicide in a two-pass system. Depending on the weed spectrum in your field, such as fields without heavy Palmer amaranth and waterhemp pressure, Corvus may still be a great one-pass option.

A recommended two-pass program starts with a pre-emergence application of Corvus herbicide. The second pass should include a postemergence product such as Laudis® herbicide (27). If using Laudis following an application of Corvus, add another effective herbicide with a different mode of action, such as DiFlexx®(4) herbicide or atrazine, to ensure you are using multiple modes of action in your weed control.

Another pre-emergent herbicide Bayer offers corn growers is Balance® Flexx (27). Follow a pre-emergent application of Balance Flexx with a postemergence herbicide to control multiple weed flushes. Balance Flexx has the unique power to reactivate with as little as a half-inch of rain to control late-emerging weeds. It controls glyphosate-, triazine-, PPO- and ALS-resistant weeds, including resistant marestail, common ragweed, waterhemp and Palmer amaranth. Balance Flexx even controls tough grasses, such as woolly cupgrass.
Balance Flexx fits into many cropping systems. Its superb weed control power combined with state-of-the-art crop safety innovation enables growers to readily rotate from corn to other key crops with little or no delay. 

Capreno® herbicide (2, 27) is a post-emergence herbicide option for corn from Bayer. It has the longest-lasting residual of any post product on the market. With multiple modes of action, Capreno controls more than 65 grasses and broadleaves, including those resistant to glyphosate, PPO, ALS, dicamba and triazines.

Wheat Solutions for Russian Thistle Management

Huskie® herbicide (6, 27) is available to wheat growers in 40 states and includes a chemistry for use in cereals that provides multiple modes of action (MOA). Huskie controls many broadleaf weeds such as kochia, Russian thistle, prickly lettuce and wild buckwheat—including ALS- and glyphosate-resistant biotypes. Huskie® Complete herbicide (2, 27, 6) is available to wheat growers in Colorado, North Dakota, South Dakota, Minnesota, Montana, Wisconsin and Wyoming. This all-in-one wheat herbicide is a combination of Huskie plus thiencarbazone that provides grass control. Together, these modes of action provide good control of green and yellow foxtail along with 50 grass and broadleaf weeds.

Additionally, growers can use Wolverine® Advanced (1, 6, 27) herbicide to control 69 different grasses and broadleaf weeds in wheat, thanks to three modes of action in a single product. Wolverine Advanced provides the same unique broadleaf control found in Huskie with the addition of ACCase grass chemistry to control green and yellow foxtail and barnyardgrass. This wheat herbicide is an excellent tool to consider as grass chemistry rotation partner to manage weed resistance.

Visit the Cereals Expert section for information on additional herbicide products Bayer offers as part of an integrated weed management program for wheat.

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