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PNW Conservation Tillage Handbook Series
Chapter 3 - Residue Management Considerations, No. 20, May 1998

Russian Thistle Skeletons Provide Residue

In Wheat-Fallow Cropping Systems 

Authors/Funding: William Schillinger is a dryland research agronomist, Department of Crop and Soil Sciences, Washington State University, P.O. Box B, Lind, WA 99341, email: (schillw@wsu.edu); Robert. Papendick is a soil scientist (retired), USDA-ARS, Pullman, WA; Roger Veseth is an extension conservation tillage specialist, Washington State University and University of Idaho, Moscow, ID; Frank Young is a research agronomist, USDA-ARS, Pullman, WA. Harry Schafer is a WSU agricultural research technician, Ritzville, WA; Bruce Sauer is farm manager of the WSU Dryland Research Station, Lind, WA. Funding for this study was partially provided by the Solutions to Economic and Environmental Problems (STEEP II) Program and the Columbia Plateau Wind Erosion/Air Quality Project.


Maintaining adequate residue to prevent wind and water erosion is often difficult in low-precipitation (less than 12 inch annual) winter wheat (Triticum aestivum L.)-fallow regions of the Pacific Northwest. This is especially true for spring-sown wheat, and for winter wheat in low-moisture conditions. In these situations, Russian thistle (Salsola iberica) can be a major weed and often produces more biomass than the crop it infests. In a 4-year study, we measured the effect of three tillage management treatments: i) traditional (tillage only); ii) minimum (herbicides and tillage), and iii); delayed minimum (herbicides and delayed tillage), on retention of above-ground wheat residue and dead Russian thistle plants or "skeletons" during the fallow cycle. Russian thistle infestation occurred two of the four years when winter wheat failed and was replaced by spring wheat. Traditional post-harvest tillage caused most Russian thistle skeletons to be wind blown from plots by late fall, but plants remained anchored in the soil when herbicides were used for post-harvest thistle control. Traditional primary spring tillage with a field cultivator or tandem disc further reduced surface cover compared to minimum tillage treatments. During two fallow cycles where Russian thistle infested the previous spring wheat crop, thistle skeletons on the soil surface averaged 280 and 40 vs. 1220 and 240 lb/acre in late fall and end of fallow in traditional tillage compared to minimum tillage treatments, respectively. Traditional tillage also reduced surface wheat residue compared to minimum tillage plots on all sampling dates. Russian thistle skeletons can be retained in place using conservation tillage during fallow, where they become an important source of surface cover to combat erosion in years when crop residues are extremely low.


Growers in low-precipitation dryland areas of the inland Pacific Northwest practice a wheat - fallow rotation where only one crop is grown every two years. Maintaining adequate surface residue for erosion control is often difficult. In low crop production years, Russian thistle is a major weed which can produce more dry matter by grain harvest than the wheat crop it infests. In a 4-year tillage management study, we consistently retained the most residue during fallow using minimum tillage practices compared to traditional tillage. In addition to wheat residue, we retained dead Russian thistle plants as an important source of surface cover using minimum tillage, whereas thistles were wind-blown from the field or buried with traditional tillage. Results show the value of conserving Russian thistle skeletons for erosion control in low crop residue situations when thistles are likely to be present in large amounts.


Wind and water erosion are major agronomic and environmental concerns in the low-precipitation (less than 12 inch annual) dryland wheat production region in eastern Washington and north-central Oregon. A biennial wheat-summer fallow rotation has been practiced in this 3.5 million acre region since native bunch grass and sagebrush was plowed in the 1880's. In drought years, or when winter wheat is replaced by a spring crop, residue production is low, and growers frequently have difficulty conserving sufficient surface cover to retard erosion during the subsequent fallow cycle. The most effective management practice for protecting soil from erosion during fallow is to maintain adequate surface residue (Horning and Oveson, 1962). Detailed descriptions of the relationship between soil cover and wind erosion loss have been reported by Bilbro and Fryrear (1994). Maximum levels of surface residue during the fall and winter reduces water runoff during the winter and increases over-winter soil water storage which benefits subsequent grain yield (Lindstrom, 1974; Ramig and Ekin, 1991; Wilkins et al., 1988). Tillage channels or slots are effective for increasing water infiltration when rain or snow melt occur on frozen soils (Zuzel and Pikul, 1987).

Russian thistle is a summer-annual weed, first reported in the United States in South Dakota in 1877 (Dewey, 1893). By the 1890's, the weed had spread to the Pacific Northwest (Young, 1991) where it quickly became the dominant broadleaf weed in low-precipitation dryland wheat areas.

Russian thistle grows during both the crop and fallow cycles. A uniform and well-established stand of winter wheat will suppress Russian thistle. On the other hand, spring wheat or drought stressed winter wheat are much less competitive and more subject to thistle infestation. Growers plant spring wheat to replace winter wheat because of: i) inadequate fall stand establishment; ii) winter kill, and; iii) the need to control winter-annual grassy weeds (Cook and Veseth, 1991). Russian thistle infestation is frequently acute in spring wheat due to less early growth and less canopy closure compared to winter wheat (Young, 1986). Spring wheat yield depression due to Russian thistle is most severe during drought years (Young, 1988). Russian thistle has an efficient C4 photosynthetic pathway with high water use efficiency (Fowler and Hageman, 1978).

Russian thistle rapidly produces dry matter and sets seed after wheat harvest (Young et al., 1995), by extracting soil moisture below the available limit for wheat. The optimum time for post-harvest control of Russian thistle is 10-to 14-days after harvest. Growers generally either till the soil with V-shaped sweeps or use herbicides after grain harvest to control Russian thistle. After primary tillage in the spring, rodweeders are used as secondary tillage to control thistles and other weeds. Rodweeders operated at depths greater than 3 inches retain surface residue and roughness more effectively for erosion control compared to shallow depths (Schillinger and Papendick, 1997).

Although Russian thistle often has negative agronomic effects, it has some beneficial attributes. During the dust bowl years in the 1930's, Russian thistle was used as emergency forage for cattle (Cave et al., 1936). Protein in Russian thistle hay can be as high as 23% (Boerboom, 1993), and the plant has potential as an energy source as processed pellets and compressed fireplace logs (Foster et al., 1980).

Because Russian thistle often produces substantial dry matter both before and after wheat harvest, it is possible that the weed could be an important source of surface cover for erosion control during the fallow cycle. No previous research has been reported on possible benefits of Russian thistle in conservation systems. The objective of this study was to: (i) document the extent of Russian thistle infestation in marginal wheat production years and; (ii) determine if dead thistles can be conserved during fallow as a significant source of surface cover in low crop residue situations.


A 4-year tillage management study was conducted between August 1993 and September 1997 at the Washington State University Dryland Research Station at Lind, WA. Long-term (82-year) average annual precipitation at the station is 9.5 inches. The soil is Shano silt loam with less than 1% organic matter in the surface 4 inches. Soil depth is greater than 6 feet. Wind tunnel tests have shown that this soil, when left unprotected (i.e., bare, tilled, dry, non-crusted), is one of the most susceptible to wind erosion and suspended dust emissions within the Columbia Plateau of eastern Washington (Saxton et al., 1996).

The experimental design was a randomized complete block of three tillage management treatments replicated four times. Each plot was 150 by 60 feet, which allowed use of commercial-size farm equipment. Paired adjacent parcels of land were used so that data could be collected from both crop and fallow phases of the study each year.

Tillage Management Treatments

The three tillage management systems compared in this study were: (i) Traditional tillage - conventional frequency and timing of tillage operations using implements commonly used by growers; ii) Minimum tillage - conventional frequency and timing of tillage operations, but herbicides were substituted for tillage when feasible and a non-inversion V-sweep implement was used for primary spring tillage, and; iii) Delayed Minimum tillage - similar to minimum tillage except primary spring tillage with a non-inversion V-sweep was delayed until at least late May. A list of field operations and timing for the study are shown in Table 1.

In traditional tillage, post-harvest tillage was conducted in August of 1993, 1994, and 1995 with overlapping 14-inch-wide V-sweeps to kill Russian thistle by severing the tap root. Russian thistle was not present in August 1996 and post-harvest sweeping was not required. Plots were chiseled in October after fall rains to a depth of 10 inches with straight-point shanks spaced 2 feet apart to create channels for controlling frozen soil runoff during the winter.

Plots were sprayed with glyphosate (Roundup) herbicide in late winter to control weeds. Primary tillage was conducted in March with two passes of a duck foot cultivator with an attached harrow, or one pass with a tandem disc (Table 1). Plots were fertilized with anhydrous ammonia nitrogen in late spring and rodweeded three times to control weeds during the summer. Winter wheat was planted in 16 inch rows in early September all years with a John Deere HZ deep furrow drill.

Minimum tillage treatments were sprayed with a nonselective herbicide for post harvest control of Russian thistle in lieu of tillage with sweeps in August (Table 1). In October, the plots were chiseled or subsoiled to depths ranging from 10-to 16-inches with straight-point shanks spaced 4 feet apart (i.e., twice the shank spacing as for traditional tillage). Chiseling was not conducted in 1996. Glyphosate was applied in late winter, and primary tillage was with a non-inversion sweep implement equipped with 32-inch-wide overlapping V-blades. A rotary harrow was attached behind the wide-blade sweep to break up large clods and fill air voids. The plots were rodweeded three times during late spring and summer and fertilized with aqua ammonia nitrogen injected between the rows of the deep furrow grain drill when planting winter wheat in early September.

The delayed minimum tillage treatment was identical to the minimum tillage treatment except that: (i) primary spring tillage was delayed until late May or early June, and; (ii) only two rodweedings were conducted during late spring and summer.

All treatments were planted at the same time. Due to inadequate fall stands of winter wheat, all plots were replanted to hard red spring wheat in March of 1993 and 1995 (Table 1). Cultivar 'Butte 86' was sown @60 lb/acre in 6 inch rows with a disc drill.

Residue Measurement

Surface residue remaining from the previous crop cycle was measured several times throughout the fallow period by gathering all aboveground dry matter within a 3-ft diameter hoop. Three samples were obtained from each plot. Wheat straw and Russian thistle skeletons were separated, placed in paper bags, and allowed to air dry in a low-humidity greenhouse before weighing. An analysis of variance was conducted for both wheat straw and Russian thistle skeletons on each sampling date. Treatment means were considered significantly different if the P-value was <0.05, using Fisher's protected least significant difference.


Russian thistle produced significant biomass during two crop cycles when spring wheat replaced winter wheat due to inadequate seed zone moisture for stand establishment. Spring wheat residue at the beginning of both the 1993-1994 and 1995-1996 fallow cycles was less than 1300 lb/acre, whereas Russian thistle dry matter was greater than 1550 lb/acre (Figs. 1 and 2). These data agree with other studies showing Russian thistle capable of producing more total dry matter than the spring wheat crop it infests (Young, 1988).

Fig. 1. Above-ground hard red spring wheat residue and Russian thistle skeletons during the 1993-1994 fallow cycle as affected by traditional, minimum, and delayed minimum tillage. Different letters within sampling dates indicates significant treatment differences (P < 0.05).

In traditionally-tilled plots, post-harvest tillage reduced surface wheat residue and Russian thistle skeletons compared to minimum tillage where Russian thistle was killed by post harvest application of herbicides (Table 1, Figs. 1 and 2). During the fall and winter, the majority of Russian thistle skeletons were wind-blown from the field in traditionally-tilled plots because the tap root had been severed by the post-harvest sweep operation. Conversely, when herbicide was used for post harvest control in the minimum-tilled treatments, most Russian thistle plants remained anchored in the soil or trapped by standing wheat stubble. (Figs. 1 and 2).

Fig. 2. Above-ground hard red spring wheat residue and Russian thistle skeletons during the 1995-1996 fallow cycle as affected by traditional, minimum, and delayed minimum tillage.

Surface wheat residue and Russian thistle skeletons were always lower in the traditional tillage than in minimum tillage throughout the spring and summer in both the 1993-1994 and 1995-1996 fallow cycles (Figs. 1 and 2). Highest retention of surface residue in the spring was achieved with delayed minimum tillage. Differences in residue levels between minimum and delayed-minimum treatments did not persist until the end of the fallow cycle (Figs. 1 and 2). A benefit of delayed minimum tillage compared to minimum tillage was the need for one less rodweeding operation during the summer (Table 1), which conserves energy and labor.

Fig. 3. Above-ground hard red winter wheat residue during the 1994-1995 fallow cycle (A), and soft white winter wheat residue during the 1996-1997 fallow cycle (B), as affected by traditional, minimum, and delayed minimum tillage.

At the end of the 1993-1994 fallow cycle, only 230 lb/acre of wheat residue and 55 lb/acre of Russian thistle skeletons remained on the soil surface in traditionally tilled plots (Fig. 1). Wheat growers in the dryland areas of the Pacific Northwest are required to maintain a minimum of 350 lb/acre surface residue on highly erodible land in order to participate in government farm programs. With traditional tillage, we were unable to meet this requirement in the 1993-1994 fallow cycle.

In contrast, residue compliance was easily met with combined wheat residue and Russian thistle skeletons exceeding 740 lb/acre in the minimum and delayed-minimum tillage treatments. Residue compliance was marginally met (380 lb/acre) with traditional tillage at the end of the 1995-1996 fallow cycle (Fig. 2), but residue was likely reduced a further 20% after planting winter wheat with deep furrow drills (McClellan, 1988). More than 750 lb/acre combined surface cover remained with minimum and delayed-minimum tillage at the end of the 1995-1996 fallow cycle (Fig. 2).

Russian thistle did not infest good stands of hard red winter wheat (cv. 'Buchanan') and soft white winter wheat (cv. 'Eltan') planted in early September of 1993 and 1995, respectively. Residue production from winter wheat exceeded 1800 lb/acre, and we maintained more than 500 lb/acre surface cover with traditional tillage and more than 1,000 lb/acre for the minimum tillage treatments at end of both the 1994-1995 and 1996-1997 fallow cycles (Fig. 3).


Tillage management affected surface wheat residue and Russian thistle skeleton retention throughout the fallow cycle. In low production years, Russian thistle produced more dry matter at grain harvest than the spring wheat crop it infested. By using herbicides rather than tillage for post harvest thistle control and non-inversion sweeps for primary spring tillage, we consistently retained more wheat residue and Russian thistle skeletons on the soil surface throughout the fallow cycle than was possible with traditional tillage. We could not retain the minimum required quantity of surface residue for erosion control during the 1993-1994 fallow cycle using traditional tillage, but easily met this requirement using minimum tillage.

Russian thistle did not infest well established stands of winter wheat and maintenance of adequate surface residue during the subsequent fallow cycle was achieved even with traditional tillage. Conserving dead Russian thistle plants in low crop residue situations can be beneficial for meeting residue requirements and controlling both wind and water erosion.


Bilbro, J.D., and D.W. Fryrear. 1994. Wind erosion losses as related to plant silhouette and soil cover. Agron. J. 86:550-553.

Boerboom, C. Russian thistle. 1993. Pacific Northwest Extension Publication 461. Washington State University, University of Idaho, and Oregon State University.

Cave, H.W., W.H. Riddell, and J.S. Hughes. 1936. The digestibility and feeding value of Russian thistle hay. J. Dairy Sci. 19:285-290.

Cook, R.J., and R.J. Veseth. 1991. Wheat health management. APS Press, St. Paul, MN.

Dewey, L.H. 1893. The Russian thistle and other troublesome weeds in the wheat region of Minnesota and North and South Dakota. USDA Farmers' Bull. 10. 16 p.

Foster, K.E., R.L. Rawles, and M.M. Karpiscak. 1980. Biomass potential in Arizona. Desert Plants 2(3):197-200.

Fowler, J.L., and J.H. Hageman. 1978. Nitrogen fertilization of irrigated Russian-thistle forage. I. Yield and water use efficiency. Agron. J. 70:989-992.

Horning, T.R., and M.M. Oveson. 1962. Stubble mulching in the Northwest. Agric. Info. Bull. No. 253. USDA-ARS and Oregon Agric. Exp. Sta., Corvallis, OR.

Lindstrom, M.J. 1974. Wheat-fallow management practices in the low rainfall areas of the United States Pacific Northwest. In Tillage and cultural practices for wheat under low rainfall conditions. Proc. 2nd Regional Wheat Workshop, Ankara, Turkey. 6-11 May. Rockefeller Foundation, New York.

McClellan, R.C. 1988. Small grain residue production in eastern Washington dry-farmed croplands. Agronomy Tech. Note No. 10. USDA-Soil Conserv. Service, Spokane, WA.

Ramig, R.E., and L.G. Ekin. 1991. When do we store water with fallow? pp. 56-60. Oregon Agric. Exp. Stn. Special Report No. 680, Corvallis, OR.

Saxton, K.E., L.D. Stetler, and L.B. Horning. 1996. Principles to predict and control wind erosion and dust emissions from farm fields. p. 7-12. In R. Papendick and R. Veseth (ed.) Northwest Columbia Plateau Wind Erosion Air Quality Project: An Interim Report of Solutions in Progress. Washington State Univ. Misc. Pub. No. MISC0184.

Schillinger, W.F., and R.I. Papendick. 1997. Tillage mulch depth effects during fallow on wheat production and wind erosion control factors. Soil Sci. Soc. Am. J. 61:871-876.

Wilkins, D.E., B.L. Klepper, and P.E. Rasmussen. 1988. Management of grain stubble for conservation tillage systems. Soil Tillage Res. 12:25-35.

Young, F.L. 1986. Russian thistle (Salsola iberica) growth and development in wheat (Triticum aestivum). Weed Sci. 34:901-905.

Young, F.L. 1988. Effect of Russian thistle (Salsola iberica) interference on spring wheat (Triticum aestivum). Weed Sci. 36:594-598.

Young, F., R. Veseth, D. Thill, W. Schillinger, and D. Ball. 1995. Managing Russian thistle under conservation tillage in crop-fallow rotations. Pacific Northwest Extension Publication 492. University of Idaho, Oregon State University, and Washington State University.

Young, J.A. 1991. Tumbleweed. Scientific Am. 82-87.

Zuzel, J.F., and J.L. Pikul, Jr. 1987. Infiltration into a seasonally frozen agricultural soil. J. Soil Water Conserv. 42(6):447-450.

The Pacific Northwest Conservation Tillage Handbook is a large three-ring binder handbook that is updated with new and revised Handbook Series publications. It was initiated in 1989 as a PNW Extension publication in Idaho, Oregon and Washington. Updates to the Handbook are provided when the updating card is returned. By 1997, 34 new PNW Conservation Tillage Handbook Series have been added to the original 98 publications Copies are available for $20 through county extension offices in the Northwest or ordered directly by calling state extension publication offices: Idaho -- (208) 885-7982; Oregon -- (541)-737-2513; Washington -- (509) 335-2999 (some shipping and handling charges and sales tax may apply).

It's now accessible on the Internet! All of the PNW Conservation Tillage Handbook and Handbook Series are being put on the World Wide Web Home Page (http://pnwsteep.wsu.edu) titled Pacific Northwest STEEP III Conservation Farming Systems Information Source. The Web site also contains recent issues of the PNW STEEP III Extension Conservation Tillage Update, listings of other conservation tillage information resources, coming events and much more. For more information on the Handbook or updates to the Handbook, contact Roger Veseth, WSU/UI Conservation Tillage Specialist, Plant Soil and Entomological Sciences Department, University of Idaho, Moscow, ID 83844-2339, phone 208-885-6386, FAX 208-885-7760, e-mail (rveseth@uidaho.edu).

Pacific Northwest Conservation Tillage Handbook Series publications are jointly produced by University of Idaho Cooperative Extension System, Oregon State University Extension Service and Washington State University Cooperative Extension. Similar crops, climate, and topography create a natural geographic unit that crosses state lines in this region. Joint writing, editing, and production prevent duplication of effort, broaden the availability of faculty, and substantially reduce costs for the participating states.

For herbicide application recommendations, refer to product labels and the Pacific Northwest Weed Control Handbook, an annually revised extension publication available from the extension offices of the University of Idaho, Oregon State University and Washington State University. To simplify information, chemical and equipment trade names have been used. Neither endorsement of named products is intended, nor criticism implied of similar products not mentioned.

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