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Pacific Northwest Conservation Tillage Handbook Series No. 16
Chapter 5 - Weed Control Strategies, July 1995


Russian Thistle Management under Conservation Systems in Pacific Northwest Crop-Fallow Regions 

Frank Young, Research Agronomist, USDA-Agricultural Research Service, Pullman, WA
Roger Veseth, Extension Conservation Tillage Specialist, Washington State University and University of Idaho, Moscow, ID
Donn Thill, Weed Scientist, University of Idaho, Moscow
William Schillinger, Area Extension Agronomist, Washington State University, Ritzville
Dan Ball, Weed Scientist, Oregon State University, Pendleton, OR.

Introduction

Russian thistle (Salsola iberica) is a summer-annual broadleaf weed commonly found in many of the low precipitation cropland areas of the Pacific Northwest. This weed causes serious production problems in crop, following harvest, and during summer fallow. Control of Russian thistle is an important management focus for many growers as they adapt their farming systems to meet changing environmental and economic demands.
Growers strive to continually develop farming systems that improve cropland productivity, protect the environment and increase profitability. Tillage to control Russian thistle after harvest and during the summer fallow season can reduce crop residue on the soil surface and decrease surface roughness, which increases the potential for soil erosion and soil water loss by evaporation and runoff. Use of herbicides in the sulfonylurea family (such as Glean and Finesse) provided effective Russian thistle control in the 1980's, but widespread Russian thistle resistance to these crop protection chemicals has resulted in the need to develop other management options.
Fortunately, PNW research and the experiences of an increasing number of growers show that good Russian thistle control, effective soil conservation, and profitable farming operations are not mutually exclusive. Management strategies with improved cultural and herbicide options for Russian thistle control are providing effective weed control in profitable conservation systems.
This publication reviews aspects of Russian thistle biology as it relates to management and outlines some key considerations for management strategies. The four primary goals for Russian thistle management strategies are to:
  1. Reduce Russian thistle seed production and seedbank in the soil
  2. Reduce wind and water erosion potential
  3. Increase soil water storage and crop yield potential
  4. Increase profitability...the bottom line
More detailed information on the biology and identification of Russian thistle is available in "Russian Thistle" Pacific Northwest Extension Weed Series bulletin PNW 461. It is available through local extension offices in the Northwest.

Russian Thistle Biology Related to Management Considerations

Seed Dormancy and Longevity in Soil

Most newly-produced Russian thistle seeds are dormant for a short period of time after maturity in the fall. Seed dormancy decreases over winter and is almost nonexistent by spring, allowing germination to occur over a wide range of temperature and moisture conditions.
Research under irrigated conditions indicates that Russian thistle seed viability in the soil declines greatly within 2 years. Under irrigated conditions at Prosser, WA, about 99% of the seeds germinated or did not survive in the soil past the first year. In dryland wheat-fallow areas, seed longevity in the soil may be longer, and research has been initiated to determine this time period. Russian thistle seed is soft and porous, characteristics that contributes to its lack of longevity and ability to germinate rapidly. Management strategies that focus on preventing seed production are effective because Russian thistle has both limited seed dormancy and longevity in the soil.

Seed Distribution

Russian thistle has a unique mechanism for increasing the area of infestation -- mature plants break at the ground level and they tumble with the wind to disperse seeds. An experiment was conducted in eastern Washington in 1991 and 1992 to measure movement of Russian thistle and seed dispersal in the wind. Average estimated seed number per plant at the start of the experiment was 61,700. Plant movement was highly correlated with wind direction. Some plants moved up to 2.5 miles in 6 weeks, while other plants moved only 200 feet because of variable winds and being compressed with snow or frozen into wheat stubble. Average percent seed loss for the tumbling plants was 57 percent.
A special layer of cells where the plant is connected to its roots enables plants to break away with the wind during winter months after seeds are mature. Cutting off mature Russian thistle plants with tillage implements in the fall also facilitates spreading of seeds by releasing the tumbling plants -- a factor to consider when selecting tillage implements and timing of operations. Because undisturbed Russian thistle can produce 150,000 to 200,000 seeds and seed distribution is rapid and widespread, there is a high potential for future infestations.

Seed Germination and Emergence

Russian thistle seeds require only a short moist period to permit rapid germination and emergence from the soil. As growers know, Russian thistle can emergence in significant numbers in crop and fallow after very light rains (about 0.1 inch) on dry soil (Fig. 1). Germinating seeds also can withstand several wetting and drying cycles until there is sufficient moisture for emergence and establishment. The primary reason for this unique survival trait is that Russian thistle seeds consist of fully differentiated, coiled "seedling" in the form of a spiral helix, ready to take quick advantage of short periods of favorable environmental conditions.
 
Fig. 1. Russian thistle emergence with increasing amounts of rainfall (Source: Dwyer, D. D. And K. Wolde-Yohannis. 1972. Germination, emergence, water use and production of Russian thistle. Agron. J. 64:52-55).
Optimum temperature for Russian thistle germination ranges between 45 and 95 degrees F. Seeds can germinate under cooler conditions when night temperatures are below freezing, if daytime temperatures are above freezing. However, young seedlings are very susceptible to frost. Emergence typically begins in late March-early April, extending through the summer when sufficient precipitation occurs.
One factor limiting Russian thistle establishment is seed depth in soil (Fig. 2). Emergence is optimum at depths less than 0.5 to 1.0 inch, although some seedlings can emerge from 2-3 inches under favorable conditions.

Fig. 2. Russian thistle emergence from seeds buried at increasing depths in sandy loam soil compacted to a bulk density similar to a planted field. (Source of greenhouse data: Evans, R.A. and J.A. Young. 1972. Germination and establishment of Salsola in relation to seedbed environment - II. Seed distribution, germination, and seedling growth of Salsola and microenvironmental monitoring of the seedbed. Agronomy Journal. 64:219-224; Source of field data from Lind, WA: Young, F.L. 1982. Unpublished data.)
Russian thistle establishment also can be limited by compacted soils. The roots cannot effectively penetrate compacted soil as the coiled embryo unwinds during germination. In addition, shoot emergence can be restricted by crusted surface soil, even if seeds are buried shallowly. However, seedlings can emerge through cracks in the soil surface.

Plant Growth After Establishment

Flowering commonly begins around mid-June. To effectively prevent seed production and reduce weed competition, Russian thistle should be controlled within 4 weeks after emergence. Flowering increases greatly after crop harvest when about 90% of the Russian thistle growth and the majority of seed set commonly occur. Russian thistle usually remain small in a competitive winter wheat crop but grow rapidly immediately after harvest. Russian thistles grow larger in a less competitive crop, such as spring wheat, and even though the top portion of the Russian thistle plants are cut by the combine, they can regrow quickly after harvest. This rapid growth after harvest is why Russian thistle not controlled in crop should be controlled within about 10 to 14 days after harvest to effectively reduce seed and biomass production, and soil water use. Russian thistle is indeterminate, therefore it continues to flower and produce seed as long as conditions allow, typically until a killing frost at around 25 degrees F or less, or until several successive frosts just below freezing occur.
Studies indicate that Russian thistle is one of the most efficient plants in the world at producing plant dry matter per unit of water used. Russian thistle roots extract water from the soil very efficiently and can extend to a depth of 5 feet with lateral spread of 6 feet. Winter wheat grown on silt loam soils in the PNW commonly extracts water down to 4.5 percent (by volume) by harvest time. Russian thistle roots will continue to extract soil water when it is no longer available to the wheat plants. It is important to control Russian thistle postharvest to prevent excessive soil water loss.

Crop Competition

Growing a competitive crop is a very important management tool to reduce Russian thistle growth and seed production. Growth of Russian thistle is suppressed greatly when the crop establishes first, over-tops the weed, and has adequate moisture and nutrients. Conversely, Russian thistle causes the greatest yield losses in crops during drought conditions, with poor stands, and planted late.
Russian thistle usually reduces crop yield more in spring wheat than in winter wheat. A study of Russian thistle growth and development in summer fallow, spring wheat, and winter wheat was conducted at Lind, WA in 1982 and 1983. Russian thistles were established in early April and allowed to grow until killed by frost in October. Dry weight of Russian thistle grown in winter wheat was about 75% less than those grown in spring wheat and 98% less than under fallow with no weed or crop competition (Fig. 3). After harvest, Russian thistle that had grown in spring wheat used about four times more water than plants grown in winter wheat. Results from these and additional experiments at Lind show that winter wheat reduced Russian thistle emergence 44%, seedling survival 42% and seed production 74% compared to spring wheat. When Russian thistle was not controlled through the growing season or after harvest, single plants produced 150,000 seeds in undisturbed fallow, 17,400 in spring wheat, and 4,600 in winter wheat.

Fig. 3. Russian thistle growth in fallow and when competing with spring and winter wheat at Lind, WA. Russian thistle emerged in early April. Winter and spring wheats were harvested at points marked ww and sw, respectively. (Source: Young, F.L. 1986. Russian thistle (Salsola iberica) growth and development in wheat. Weed Sci. 34:901-905).
Even though spring wheat provides less competition against Russian thistle than does winter wheat, management practices which increase crop competitiveness can help suppress Russian thistle. The same is true with the competitiveness of winter wheat and other crops. Research data on weed/crop competition with spring wheat in 1983-85 at Lind reveal the importance of early spring wheat establishment to improve crop competitiveness (Table 1). Although Russian thistle density was highest in 1984, yield loss was much lower than in 1983 or 1985. The low effect of Russian thistle in 1984 was attributed partially to seeding wheat one week earlier than the other years and the corresponding crop emergence two weeks ahead of Russian thistle, compared to one week ahead in the other two years. Although weed densities were similar in 1983 and 1985, Russian thistle was much more competitive in 1985 when rainfall was low.
Table 1. Spring wheat yield losses from Russian thistle competition, 1983-85, WSU Dryland Research Unit, Lind, WA.

Year Russian
thistle
density
Seeding
date
Wheat
emergence
ahead of
Russian
thistle
March-June
rainfall
Wheat
yield
loss
  (plants/sq ft)     (in) (%)
1983 5 March 18 1 week 3.9 31
1984 10 March 9 2 weeks 5.5 11
1985 4 March 15 1 week 1.8 55

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

Managing Wheat and Russian thistle Residue

Maintaining enough residue on the soil surface to control wind erosion is a major concern in the low-rainfall dryland wheat regions. Growers should consider dead Russian thistle plants or "skeletons" as a residue source in postharvest residue management decisions. The erosion control challenge in the very dry areas is three-fold: 1) not enough crop residue is produced; 2) soils are generally coarse textured and seldom retain adequate soil cloddiness; and 3) traditional soil management techniques often reduce soil roughness and bury most of the crop residue. By the end of the fallow period the surface soil mulch is often powdery and deficient of surface residue. In these dry environments, Russian thistle skeletons can provide an important source of residue for water conservation and erosion control.
A residue management experiment was initiated at Lind, WA during the 1993-94 fallow cycle to determine how much tillage could be reduced and still maintain an agronomically feasible production system. Traditional, minimum, and delayed minimum tillage systems were evaluated (Table 2).
Preliminary results of this study indicate that significantly more winter wheat and Russian thistle residue can be retained through of the fallow cycle in the minimum tillage systems and that Russian thistle skeletons can be an important contributor to the total surface residue (Fig. 4).
Table 2. Field operations conducted in the tillage management experiment at WSU Dryland Research Unit at Lind, WA during the 1993-94 fallow cycle (W. Schillinger, WSU, Ritzville).

Date Traditional
tillage
Minimum tillage Delayed
minimum tillage
8/93 Sweep
-12" spacing
Herbicide-
Landmaster
@ 48 oz
Herbicide-
Landmaster
@ 48 oz
10/93 Chisel
-24" spacing
Chisel
-72" spacing
Chisel
-72" spacing
2/94 Herbicide-
Roundup
@ 12 oz
Herbicide-
Roundup
@ 12 oz
Herbicide-
Roundup
@ 12 oz
3/94 Cultivator +
harrow
(2 passes)
Undercutter +
rolling harrow
 
4/94 Anhydrous N
injection
@ 40 lb
   
5/94 First
rodweeding
First
rodweeding
Undercutter +
rolling harrow
6/94 Second
rodweeding
Second
rodweeding
First
rodweeding
7/94 Third
rodweeding
Third
rodweeding
Second
rodweeding
9/94 Seeding Seeding+aqua
N @ 40 lb
Seeding+aqua
N @ 40 lb
Where Russian thistle roots were severed by postharvest sweeping under traditional tillage, most of the Russian thistle skeletons had blown away by the November 7 measurement of Russian thistle residue. In the two minimum tillage treatments, a postharvest herbicide application for Russian thistle control and fall chiseling with 72-inch shank spacing left most of the Russian thistle skeletons anchored overwinter and resulted in a higher percentage of overwinter precipitation stored in the soil. In general, leaving more residue on the soil surface overwinter results in increased soil water storage.

Herbicide Resistance

In the early 1980's, the registration of sulfonylurea herbicides provided a great advancement in Russian thistle control. However, the development of extensive Russian thistle resistance to this herbicide family has set back control efforts. About 70% of the sites infested with Russian thistle in eastern Washington now contain plants that are resistant to sulfonylurea herbicides. Resistance has also been confirmed throughout the Columbia Basin in Oregon and in Idaho. Sulfonylurea herbicides used in wheat and/or fallow cropland have included Glean, Ally, Finesse, Express, Harmony-Extra and Amber.
A key reason for rapid development of Russian thistle herbicide resistance are the "same" syndrome:
  1. Same herbicide or herbicide family used once or more each year for successive years.
  2. Same crop (eg. in the wheat-fallow-wheat rotation).
  3. Same field.
  4. Same target weeds.
Also, the tumbling action of the Russian thistle plants contributed to the rapid spread of the problem within and between fields. For more information on preventing and controlling herbicide resistant weeds, see Pacific Northwest Extension publication PNW 437 "Herbicide-Resistant Weeds and Their Management." Copies are available through local county extension offices in Idaho, Oregon and Washington.

Fig. 4. Wheat residue (top) and Russian thistle skeletons (bottom) as affected by tillage method on three sampling dates during the 1993-94 fallow cycle at WSU Dryland Agricultural Research Unit at Lind , WA (W. Schillinger, WSU, Ritzville). Averages followed by the same letter are not significantly different at the 5% probability level.

Windows of Opportunity for Russian Thistle Control

There are several opportunities to reduce Russian thistle competitiveness and seed production during the crop-fallow rotation or other crop rotations in the low rainfall zones. Making the best use of each available management option throughout the rotation will provide the best overall control. The following are a number of "windows of opportunity" for Russian thistle control:
In Crop - Several herbicides are available for control of Russian thistle with varying degrees of effectiveness and costs. See the current year Pacific Northwest Weed Control Handbook for specific herbicide recommendations. Most recommended herbicides control Russian thistle best when applied to 2-inch tall or smaller plants. Remember that production management practices that increase crop competitiveness also reduce Russian thistle growth and seed production. It is important to minimize the potential for increasing problems with herbicide resistance through rotation of herbicides with different modes of action (see PNW 437).
Preharvest - Appropriate nonselective herbicides registered for preharvest application can accelerate dry-down of Russian thistle, improve harvest efficiency and effectively control Russian thistle for about 60 days after harvest.
Postharvest - Control Russian thistle with nonselective or broadleaf herbicides or with tillage by 10 to 14 days after wheat harvest. It is important to compare herbicide applications and tillage relative to their effects on residue retention and soil water storage over winter, during the fallow period and next winter wheat crop, as well as the cost, effectiveness of Russian thistle control, and seed production. Sweeping kills most Russian thistles but will likely result in reduced surface residue levels and overwinter water storage compared to control with herbicides.
Summer Fallow - Control Russian thistle before seed set with herbicides and/or tillage, but avoid excessive tillage, which reduces surface residue and roughness. Delay initial tillage and subsequent rod weedings for Russian thistle control as long as possible after rain during the fallow period. Rodweeding too soon after a heavy rain may also form a tillage pan which grain drill openers may have difficulty penetrating at planting time. Research has shown that operating rodweeders at deeper depths (4 inches) causes less pulverization of soil clods than when operated at shallow depths (2 inches). This may be an important management factor on soils prone to wind erosion.
Field Borders and Roadways - Control Russian thistle along field borders, roadways and other noncropped areas upwind from fields to prevent introduction or reinfestation of fields with Russian thistle. Because of the high mobility of Russian thistle skeletons in the wind and extensive seed distribution potential, an area-wide Russian thistle control strategy is needed to achieve and maintain effective control. Cooperation of neighboring upwind producers is needed for effective control of Russian thistle on a community basis if possible. Unless Russian thistle dispersal is controlled, it is difficult to manage this weed.

Management Strategy Considerations for Russian Thistle Infestations

Management strategies for Russian thistle, which focus on preventing seed production throughout the crop rotation, can reduce a serious Russian thistle infestation to a manageable level. There are a number of important biological traits and crop production options described in previous sections that need to be considered in developing Russian thistle management strategies. These include:
  • Short Russian thistle seed dormancy and seed longevity in the soil
  • Extensive period of potential Russian thistle germination from early spring through late summer
  • Extensive period of Russian thistle flowering and seed formation from early summer until a killing frost
  • Extensive Russian thistle use of soil water in crop, after harvest, and in fallow
  • Lower Russian thistle populations, growth, and seed production in a uniform stand of winter wheat than in spring wheat
  • Management practices that increase crop competitiveness reduce Russian thistle problems
  • Wind dispersal of Russian thistle seed by blowing plants can be increased with fall tillage practices that sever the plant from the roots
  • Tillage options for retention of wheat and Russian thistle residue to increase soil water storage potential and reduces erosion hazard
  • Widespread Russian thistle resistance to sulfonylurea herbicides

 

The following is a series of chronological management strategy considerations for a heavy Russian thistle infestation in a crop-fallow rotation, beginning in the crop year. It is assumed that Russian thistle is controlled on neighboring fields so reinfestations do not occur from seed sources outside the field.

Crop Year 1

  1. Plant winter wheat rather than spring wheat if possible, because it is more competitive and will help reduce Russian thistle emergence, survival, growth, and seed production. Practices that further increase winter wheat competitiveness also would be important Russian thistle management tools. At least spot apply herbicides in areas where Russian thistle may concentrate, such as drill skips, winter-killed areas, and draws where wind-blown Russian thistle skeletons collect.
  2. If spring wheat is planted, due to winterkill or other production problems, use management practices which optimize crop competitiveness with Russian thistle. These include: seed early (late February, early March) so wheat emerges ideally 2-3 weeks or more before Russian thistle; seed shallow as possible to encourage rapid emergence; place fertilizer below and near seed rows for early wheat root access and vigorous crop growth; use conservation tillage systems to minimize water evaporation which optimizes water availability to the crop. If possible, use narrow row spacings, such as 6-7 inches, to increase crop competition with Russian thistle.
  3. Use broadleaf herbicides to control Russian thistle in crop. A tank mix of herbicides with different modes of action can reduce populations and the development of herbicide resistance, but only if all herbicide mix partners equally control the weed. The goal is to kill or suppress Russian thistle in order to minimize competition with the crop, improve harvest efficiency, and reduce the potential for seed production later in the season. Herbicides should be applied before the Russian thistles exceed 2 inches in height. Remember that the first Russian thistle plants that emerge will be the most competitive. Complete control is not required. Lower cost treatments may be fine as long as they provide a reasonable level of control. However, in a severe Russian thistle infestation it may be more effective to strive for optimum control rather than suppression. It may be necessary to consider a preharvest herbicide application to control any escapes and late-germinating weeds.
  4. If Russian thistles were not controlled effectively early in the growing season, consider a preharvest nonselective herbicide. Russian thistle already has competed with the crop by that point, but seed production can be reduced greatly and soil water conserved for the following crop. A preharvest application of a nonselective herbicide often controls Russian thistle better than postharvest applications. Preharvest treatment can provide several advantages:
    1. Saves time at harvest and improve harvest efficiency.
    2. Reduces Russian thistle size, seed production, and soil water use.
    3. May eliminate the need for postharvest tillage for Russian thistle control or at least the need for a disc operation to chop Russian thistle residue.

Fallow Year 1...Beginning After Harvest

The Russian thistle management goal during fallow is to stop seed production for a 2nd year, while optimizing seed zone soil water and retention of surface residue and roughness.
Consider postharvest herbicide or tillage operations if in-crop and preharvest applications were not effective. Control practices should be applied 10-14 days after harvest to prevent prolific growth and seed production of Russian thistle. An important goal in postharvest management is to save crop residue on the soil surface for water and soil conservation during the fallow season and the next winter wheat crop, but prevent seed production as much as possible. Tillage practices should focus on water conservation and residue management as well as on Russian thistle control. If tillage is used after harvest, a sweep will provide greater residue retention and water conservation overwinter.
 

Herbicide choice can influence the subsequent management of Russian thistle residue. Non-selective herbicides applied preharvest or postharvest generally result in dry, brittle Russian thistle skeletons which help reduce weed residue problems at harvest and during fall tillage operations. Other postharvest herbicides, such as 2,4-D, can leave the Russian thistle plants tough, "leathery," and more difficult to manage.

Tillage with sweep or wide-blade undercutter implements can kill Russian thistle without excessive loss of surface residue. However, these tillage operations should be done within about 2 weeks after harvest to minimize water use, seed set and spreading of infestations due to wind distribution of severed plants. Effective control in-crop and preharvest also can help avoid the use of more intensive tillage operations, such as discing, to control Russian thistle after excessive growth occurs following harvest. Discing can reduce surface residue and roughness significantly, and consequently reduces erosion protection and water storage potential during the fallow season, and in the following winter wheat crop. Retention of Russian thistle skeletons as residue for soil and water conservation with herbicide control rather than tillage after harvest is also a consideration, particularly when crop residue production is low.

In areas where overwinter runoff on frozen soils occurs commonly, growers should consider chiseling, subsoiling or other non-inversion tillage operations to increase water infiltration. Wider shank spacings of 4-6 feet can achieve this goal with minimal disturbance of anchored Russian thistle plants and standing stubble, thus optimizing residue benefits for trapping snow and reducing evaporation.

Delay primary or first spring tillage as late as possible. Consider using herbicide treatments for Russian thistle and other broadleaf/grass weeds to delay spring tillage. On fields known to have Russian thistle infestations, delay herbicide application and tillage until after the first heavy flush of emerging Russian thistle in the spring.

Winter Wheat Crop 2

The field should have a reduced Russian thistle population after 2 years of seed bank depletion if Russian thistle control efforts have been effective in Crop Year 1 and Fallow Year 1, as long as Russian thistle plants have not moved in from neighboring fields, field borders, and non-field areas. Strive for good control again in Crop Year 2. Spot spray areas of the field infested with dense populations of Russian thistle. Russian thistle should not be a harvest problem in the 2nd crop year, but a nonselective preharvest herbicide could be used if warranted. If Russian thistle problems require postharvest attention to prevent Russian thistle seed production and soil water loss, consider a nonselective herbicide or tillage soon after crop harvest, at least as spot treatments of small Russian thistle areas and along field borders.

Fallow Year 2

Management considerations are basically the same as in Fallow 1, but there is a potential for reduced frequency of rodweedings for Russian thistle control since the Russian thistle seedbank in the soil should be reduced significantly. Another year of Russian thistle seed production should be prevented through the summer fallow. Maintain control of Russian thistle in fence rows and field margins.

Winter Wheat Crop 3

At this phase of the crop rotation, a Russian thistle maintenance control program should effectively keep the problem in check. Continue a good general broadleaf weed control program in crop. Russian thistle suppression may be all that is required. Postharvest spot treat small Russian thistle areas in draws and along field borders, and continue to monitor adjacent fields and non-cropped areas to reduce the potential of reinfestations.

Additional Copies and Information

Additional copies of this PNW Conservation Tillage Handbook Series publication are available through county extension and conservation district offices in applicable dryland areas of the Pacific Northwest. Another recent publication on weed management in the crop-fallow rotation available at these county offices is "Managing Downy Brome under Conservation Tillage Systems in the Inland Northwest Crop-Fallow Region," Handbook Series 15 in Chapter 5, published in June 1994. Copies of these and other Handbook Series can also be requested from Roger Veseth, WSU/UI Extension Conservation Tillage Specialist at (208) 885-6386, or Don Wysocki, OSU Extension Soil Scientist at 503-278-4186. The entire Handbook can be purchased through county extension offices for $20, including postage, handling and new Handbook Series publications.

For chemical control 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, trade names have been used. Neither endorsement of named products is intended, nor criticism implied of similar products not mentioned.


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.


Cooperative Extension programs and policies comply with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. The University of Idaho Cooperative Extension System, Oregon State University Extension Service and Washington State University Cooperative Extension are Equal Opportunity Employers.

     
 

Contact us: Hans Kok, (208)885-5971 | Accessibility | Copyright | Policies | WebStats | STEEP Acknowledgement
Hans Kok, WSU/UI Extension Conservation Tillage Specialist, UI Ag Science 231, PO Box 442339, Moscow, ID 83844 USA
Redesigned by Leila Styer, CAHE Computer Resource Unit; Maintained by Debbie Marsh, Dept. of Crop & Soil Sciences, WSU