Managing Cephalosporium Stripe in Conservation Tillage Systems

Chap. 4, No. 17, September 1993

Roger Veseth, Baird Miller, Stephen Guy, Don Wysocki, Timothy Murray, Richard Smiley, Maury Wiese*

Introduction

Winter wheat yields can be greatly reduce by Cephalosporium stripe when weather conditions and management practices favor the disease. Crop losses were particularly severe and widespread in the Inland Northwest in 1984 and 1993. To develop effective management strategies for the disease, growers need a basic understanding of the disease cycle and how environmental and management factors affect disease potential.”Cephalosporium Stripe Disease of Cereals,” Washington State University Extension Bulletin 1434 provides a useful guide for identifying, understanding and managing the disease. Oregon State University Extension Fact Sheet 308, “Recognizing and Controlling Cephalosporium Stripe: A Disease of Cereal Grains,” presents similar guidelines. This PNW Conservation Tillage Handbook Series publication highlights key points from these publications and recent research results for managing the disease under conservation tillage systems.

Hosts, Life Cycle and Crop Injury

Cephalosporium stripe is primarily a disease of winter wheat. However, alternate hosts include winter barley and triticale, some perennial grass crops such as brome species and orchard grass, as well as winter annual grassy weeds, such as downy brome and jointed goatgrass. The soilborne pathogen causing Cephalosporium stripe survives in infested plant residue until it decomposes. The fungus produces spores under wet, cool (40-50F) fall conditions when infested residue remains on or near the soil surface. After these spores germinate, they can penetrate and infect host plant roots primarily through root injuries associated with soil freeze-thaw cycles, frost heaving, mechanical and animal damage, and pest damage, such as from wireworms and nematodes.Once inside the root, the fungus moves upward, colonizing and eventually plugging the water-conducting tissue (xylem) of the stems and leaves. By jointing or heading time, distinct yellow stripes with a narrow brown center appear on the leaves and continue down onto the leaf sheaths and stems. Infected tillers die prematurely and set little or no seed. If seed is produced, it is usually shriveled and light in test weight, much of which can be lost through the combine at harvest.In years with severe disease levels, as in 1984 and 1993, yield reductions of 75 percent or more were reported at some locations in the region. It is estimated that for every 1 percent of the tillers with disease stripes on the flag leaf, there is about 0.8% yield loss. Infection rates of 40 to 60 percent are common in high disease years. This potentially means a 32 to 48 percent yield loss. Infection rates over 90 percent were observed in portions of some fields in 1993. In years unfavorable to the disease, up to 20 percent of the tillers can be infected and although not visually noticeable, there will still be a slight yield loss.

Environmental and Management Factors Affecting Disease Potential

The incidence and severity of Cephalosporium stripe depends on a number of environmental and management factors including: 1) amount of disease inoculum in the field; 2) seeding date; 3) varietal susceptibility; 4) weather conditions which influence the level of infection; 5) soil fertility/fertilizer applications; and 6) soil pH. Each factor is briefly covered in more detail in this section. Although these factors individually influence the amount of disease, they also interact with each other, resulting in more or less disease. The entire crop production system must be considered in order to understand how these factors influence disease potential and what combination of management practices will most effectively minimize losses from Cephalosporium stripe in the next winter wheat crop.

1) Inoculum Density

Inoculum density (number of spores in the soil) depends on: A) crop history and rotation; B) tillage and residue management practices; and C) fall weather conditions. The exact relationship between the amount of disease and amount of inoculum can not be predicted, but more inoculum increases disease potential. Only a small amount of infested straw is needed to produce a significant amount of disease if conditions are favorable for spore production in the fall and infection during the winter and spring. Some examples are presented later under the “Post-harvest Residue Management” section.

A) Crop Rotation – The higher the infection level in a winter wheat crop, or other host crops or weeds, the greater the amount of inoculum there is to infect the next wheat crop. Choice of crop rotation, and subsequent tillage and residue management practices, then influence future survival of pathogen.Cephalosporium stripe is most common in 2-yr rotations and recropped winter wheat in annual cropping areas receiving 18 inches or more of annual precipitation. It can also occur in 10-18 inch precipitation areas in winter wheat-fallow rotations or other 2-yr rotations when the fall and winter weather is conducive to disease development. The highest levels of Cephalosporium stripe are typically reported on conventional “black” fallow in a 2-year rotation when susceptible varieties are seeded early.The fungus survives from year to year in infested crop residue on or near the soil surface. After the residue decomposes, the spores can only survive independently in the soil a few months. The fungus survives only in the diseased plant residue that it colonized when the plant was alive. It does not colonize the residue of other crops. Residue from spring cereals, legumes or other non-host crops does not become colonized by the fungus and carry the pathogen from one year to the next.

A 3-year rotation, which includes two years out of winter wheat or winter barley, is a highly effective management tool for reducing inoculum levels and crop losses. A 3-year rotation also permits growers to use conservation tillage practices without increasing disease severity by allowing two years for decomposition of infested residue, thus effectively reducing inoculum levels.

Winter annual grassy weeds, such as downy brome and jointed goatgrass, are hosts for the fungus and must be controlled for the rotation to be effective. Some species of perennial grass crops, including brome grasses and orchard grass, are also hosts of the disease. If possible, winter wheat should not be grown until two years after grass takeout.

B) Tillage and Residue Management – Tillage and residue management practices influence inoculum survival and pathogen spore production in the fall. More spores are produced when infested residue remains on or near the soil surface than when it is buried at depth of about 3 inches. However, the impact of tillage and residue management practices on Cephalosporium stripe inoculum level and infection potential are complicated by several interacting factors including: crop rotation; use of tillage rotations; and the influence of surface residue on soil freezing and frost heaving. Examples of the effects of these factors are briefly reviewed.Under a 3-year rotation, tillage and residue management practices have less impact on disease potential than under a 2-year rotation because the infested residue has a longer time to decompose. The results of a study near Moscow, ID provide an example of the interactive effect of rotation and tillage practices on the potential for Cephalosporium stripe infection. The study included a 2-year winter wheat-spring pea rotation and a 3-year winter wheat-spring wheat-spring pea rotation. Three tillage systems were compared. These tillage systems remained constant for each crop (Note that growers normally vary the intensity of tillage with in crop rotations, so this study is a more severe test for conservation tillage practices than would normally occur in these rotations). Tillage practices included “conventional” tillage (moldboard plow, disk, harrow and seed with a conventional drill), minimum tillage (one-pass chisel-drill combination) and no-till (direct seeding with a no-till drill). Winter wheat was seeded in mid-October, which is somewhat later than normal for the area, resulting in a lower infection potential overall. The percent disease incidence in the 2-year rotation progressively decreased with increased intensity of tillage, with 33, 22 and 11 percent infection for no-till, minimum and conventional, respectively (Fig. 1). Under the 3-year rotation, all the tillage systems resulted in less than 10 percent infection.

Most growers already use a tillage rotation along with the crop rotation as part of their farm conservation plan. More intensive tillage is used after high residue crops, such as winter wheat, and less intensive tillage after lower residue crops, such as spring barley, pea, lentil and canola. More intensive tillage can help accelerate decomposition of infested winter wheat residue without sacrificing erosion protection, since the higher initial residue levels enable adequate retention of surface residue for erosion control and water content of the soil profile is generally low going into the wet winter season. In a wheat-fallow rotation, however, tillage intensity would need to be reduced to maintain sufficient residue through planting of the subsequent winter wheat crop.With higher surface residue levels in conservation tillage systems, soil temperature is more stable. Soils tend to freeze less often and to a shallower depth than under low-residue, conventional tillage systems. This reduction in soil freezing and frost heaving could reduce root injury and infection potential. Thus, it may be especially advantageous to retain non-infested and non-host crop residue on the soil surface to provide winter protection for winter wheat.

C) Fall Weather Conditions – The pathogen population in the soil can greatly increase under cool, wet fall conditions. Spores (conidia) are produced from infested residue and these serve as the primary inoculum for infecting young wheat plants. Wet periods with temperatures between 40 and 50F are optimum for fall spore production. While fall weather can significantly increase inoculum levels, weather conditions during the late fall, winter and early spring largely determine the level of root injury and crop infection.

2) Seeding Date

Delayed seeding can be an effective management tool to reduce Cephalosporium stripe. Early seeding and emergence of winter wheat in a 2-year rotation strongly favors Cephalosporium stripe. In fact, anything that promotes rapid fall growth, including early seeding, a high soil nitrogen level and warm, wet fall weather, will increase the potential for infection, since a larger root system provides more potential sites for root injury.

Delaying seeding tends to reduce the differences in disease potential associated with different tillage and residue management systems. Following the severe Cephalosporium stripe year of 1984, a seeding date-variety-tillage experiment was conducted in 1984-86 under a winter wheat-fallow rotation near Palouse, Washington. It is important to note that delaying the seeded date from September 20 to October 1, 1985 under minimum tillage and no-till resulted in a greater reduction in infection than did moldboard plowing at the September 20 seeding date (Fig. 2). Infection potential was slightly lower under conventional tillage at both seeding dates, although it was not statistically significant. Burning the infested residue from the 1984 crop significantly reduced infection potential at the September 20 seeding date (Fig. 3). However, a similar reduction in infection was achieved without burning by delaying the seeding date until October 1.

The importance of delaying the seeding date for reducing pathogen infection and yield loss is also influenced by varietal susceptibility. A 1991-92 Cephalosporium stripe study in a wheat-fallow rotation near Pullman, WA compared the effect of 3 seeding dates on 3 varieties. All experimental plots were inoculated with the pathogen at seeding to ensure sufficient and uniform disease potential. Percent infected stems was significantly reduced with each later seeding date (Fig. 4, bottom), although differences between varieties were not statistically different. Yield of all varieties were reduced at the September 10 and 20 seeding dates, although yield of the two more tolerant varieties, Madsen and Hill 81, were significantly higher than Stephens, a highly susceptible variety (Fig. 4, top). The September 30 seeding date appeared to be late enough to avoid most yield losses from the disease because the yield of Stephens was not significantly different from Madsen and Hill 81.

The influence of seeding date is affected by crop rotation as well. In a 3-year rotation, a more “normal” seeding date (instead of late seeding) would generally not significantly increase Cephalosporium stripe potential because of the decreased inoculum levels from more complete decomposition of infested residue. Avoiding cool, wet seeding conditions with an earlier or normal seeding date is also an effective method for minimizing damage from Pythium root rot. However, remember that earlier seeding can still favor strawbreaker foot rot, viral diseases and Hessian fly.

3) Varietal Susceptibility

None of the winter wheat varieties in the Northwest are resistant to Cephalosporium stripe, but there is a wide range of tolerance to the disease. Growing more tolerant varieties significantly reduces the risk of excessive yield losses when Cephalosporium stripe is epidemic. Tables 1 and 2 show the results of 1993 variety trials in Washington and Idaho where Cephalosporium stripe infection was very high. Yields of highly susceptible varieties were reduced up to 50 percent and test weights were also low. The new WSU variety Rod had been classified as susceptible based on earlier limited data, but it appears to be moderately susceptible based on the 1993 results.

Table 1. Percent Cephalosporium stripe infection and agronomic performance of winter wheat varieties at two locations in eastern Washington, 1993 (B. Miller, WSU).

Susceptible varieties should not be planted where there is a significant potential for Cephalosporium stripe and other disease management options are not possible. More tolerant varieties offer long-term disease benefits in addition to reduced yield losses in years of high disease potential. Table 3 provides a general index of Cephalosporium stripe tolerance of current varieties. Growing more tolerant varieties reduces the risk of infection in future winter wheat crops because their lower infection rates result in less production of inoculum. In contrast, continually growing highly susceptible varieties results in abundant inoculum production, even in years when the disease is scarce.

Table 2. Percent Cephalosporium stripe infection and agronomic performance of winter wheat varieties near Lewiston, Idaho, 1993 (S. Guy, UI).

Table 3. General Index of Cephalosporium stripe tolerance of common winter wheat and triticale, 1993 (B. Miller, WSU, and S. Guy, UI).

4) Weather Conditions for Infection

Disease severity each year is highly weather dependent! Fall weather conditions that favor early plant growth and development of an extensive root system increase the number of potential infection sites. Weather that promote infection during late fall, winter and early spring includes cold periods without snow cover which result in frozen soils, multiple freeze-thaw cycles and frost heaving. The variable intensity and frequency of soil freezing and frost heaving during the winter and early spring is one of the main reasons that the disease level fluctuates so much from year to year. The potential for infection is also increased by root injury from soil insects and nematodes, animal damage and mechanical injury from tillage or fertilizer applications.

5) Soil Fertility/Fertilizer Application

Similar to the effects of early seeding and favorable fall weather conditions which promote extensive early growth, early root access to soil with high fertility and/or the full fertilizer application for the crop can result in increased root growth and greater Cephalosporium stripe infection. The impact of nutrient availability on disease potential is greatest in early seeded winter wheat, when warm, moist soil conditions and high fertility can promote extensive root growth. It is less important with later seedings dates because root growth is slower under cooler temperatures and shorter days with lower light intensity. Remember that adequate nutrient availability for early, vigorous crop growth is important for crop establishment, winterhardiness, and improved yield potential. Although adjustments in fertilizer rates, placement and timing can influence infection potential, other management options will generally have a greater impact. Note that shanking fertilizer in established winter wheat fields can significantly increase infection potential because of the mechanical root injury.

6) Soil pH Impacts

Experiments by Murray and other researchers have shown that increasing soil acidity (reducing soil pH) increases the incidence and severity of Cephalosporium stripe in the absence of root injury. The reason for increased disease with lower soil pH is still unknown. Winter wheat may have reduced tolerance to infection at lower soil pH. Increased infection may also result from less competition from other soil microorganisms or from greater pathogen growth.

Soils with a pH lower than 6.0 favors disease development as well as spore production and survival. Under the same weather conditions, seeding date and inoculum level, more disease develops when the soil pH is less than 6.0. The fungus produces the most spores in the 3.9 to 5.5 pH range.

Survival of the fungus in infested straw also increases as soil pH declines. This is due to a broad-spectrum antibiotic produced by the fungus which apparently inhibits other microorganisms in the soil. Inhibited microbial activity slows decomposition of the residue colonized by the fungus. The antibiotic is produced more abundantly and is more active under acidic conditions. In addition to surviving longer in the slowly decomposing residue, spores also appear to survive longer in the soil as the soil pH declines. Field research trials have been initiated by Murray near Pullman to determine if the addition of liming materials to raise the pH of acidic soils results in a decrease in Cephalosporium stripe. Preliminary results have be inconclusive. 

Management of Cephalosporium Stripe under Conservation Tillage

Overview

For Cephalosporium stripe, as with most crop pests, there is no one management choice that will provide complete control. The most effective and economical control will be achieved through the use of an integrated management approach that takes into account most applicable management options. Growers need to balance practices for disease control with other yield limitations and management considerations. Management impacts on water conservation and erosion protection are just two examples.

Water Conservation – In dryland regions with predominantly winter precipitation, overwinter soil water storage is a critical yield-determining factor. Consequently, the influence of tillage and residue management practices on water storage must be considered when developing strategies for control of Cephalosporium stripe and other pests. Reduced water storage potential with intensive tillage or residue removal could reduce yield more than the disease damage. Northwest research has shown that cereal stubble left standing or chiseled overwinter commonly increases water storage by 1 to 2 inches compared to moldboard plowing or burning (see PNW Extension Conservation Tillage Handbook Series No. 14 and 17 in Chap. 3 for more details).

Erosion Protection – Most farm conservation plans specify the amounts of surface residue required to control water and wind erosion. Growers need to contact their local conservation district to make sure that the production practices they select for managing Cephalosporium stripe will provide effective erosion control and allow them to meet the goals of their farm conservation plans.The following management options can help to minimize crop losses from Cephalosporium stripe in conservation tillage systems. Keep in mind that to minimize disease potential in the next winter wheat crop, management options to reduce Cephalosporium stripe infection can be equally effective as tillage and residue management practices to reduce inoculum carryover in infested residue.

1. Use a Longer Crop Rotation – A 3-year rotation, with two years out of winter cereals, provides a highly effective control of Cephalosporium stripe and allows the most flexibility in choosing a variety, tillage system and planting date. In addition, a 3-year rotation also helps control Pseudocercosporella (strawbreaker) foot rot, Hessian fly and several soilborne root pathogens. Burial or removal of pathogen-infested residue is not necessary if a 3-year rotation is utilized. Examples of rotation crop options include non-host crops such as peas, lentils, rapeseed, canola and fallow. Spring cereals, such as spring wheat and barley, avoid infection and are good rotation crops for minimizing the disease. Some grass crops, including a number of brome species and orchard grass, can serve as disease hosts. Consequently, these grass crops should ideally be followed by two years of non-host crops before planting winter wheat.
2. Adjust Seeding Date – If a field has a history of Cephalosporium stripe and a 2-year or shorter rotation must be used, delay the seeding date until about October 1 in the Pendleton, OR and Pullman, WA areas. Optimal seeding dates in other areas will vary with elevation and precipitation zone. A more “normal” (instead of delayed) seeding date is possible under a 3-year rotation because the inoculum level will be low after infested residue decomposes over the two years out of winter cereals. Although earlier seeding can minimize Pythium root rot by avoiding cool, wet conditions favored by the disease, earlier seeding generally increases the potential for damage from strawbreaker foot rot, dryland foot rot, Hessian fly and several viruses, in addition to Cephalosporium stripe.
3. Grow More Tolerant Varieties – Grow varieties with more tolerance to Cephalosporium stripe when there is a history of the disease, particularly when a 3-year rotation is not possible and/or the seeding date can not be delayed until about October 1. Use of more tolerant varieties over time will also reduce pathogen inoculum levels and damage to future crops. Even when other effective management practices are used to decrease disease potential, susceptible varieties can still sustain yield losses from Cephalosporium stripe when weather conditions are favorable for spore production and root infection.
4. Control Volunteer Wheat and Grassy Weeds – Volunteer winter wheat, downy brome, jointed goatgrass, and other winter annual grassy weeds are hosts of the disease. They should be controlled as much as possible between crops and throughout the rotation to minimize inoculum production and carryover between winter wheat crops. Allowing them to grow overwinter can reduce or eliminate the effectiveness of crop rotation for reducing inoculum levels.
5. Utilize Protective Surface Residue – Maintain non-infested surface residue to reduce the depth and frequency of soil freezing, and consequently the potential for root injury and infection. This is particularly important for residue from spring crops and other non-host crops preceding winter wheat, since the residue does not contribute to the disease inoculum level. However, in areas where 2-year wheat-fallow rotations are practiced, it is less likely that residue cover will be sufficient to significantly reduce soil freezing and root injury.

Post-Harvest Residue Management

After a wheat crop is damaged by Cephalosporium stripe, a common question is whether the infested straw should be managed differently than usual to minimize carryover of the disease to the next winter wheat crop. Research from across the country and grower experience have shown that deep moldboard plowing or burning can be very effective in reducing inoculum carryover in the field. Although some pathogen inoculum always remains, reducing the level of inoculum can dramatically reduce the disease in the next winter wheat crop. However, even a small amount of pathogen inoculum from infested straw can cause significant infection of the next winter wheat crop if weather conditions are highly favorable for fall spore production and winter/spring infection, and a susceptible variety is planted early in a short crop rotation.

The results of a research trial near Pullman, WA during the severe Cephalosporium stripe crop year of 1983-84 show how only a small amount of pathogen inoculum can result in high infection levels. In this study, susceptible variety of winter wheat was planted on September 15, 1983 on conventionally-tilled summer fallow in a wheat-fallow rotation. To simulate a range of pathogen inoculum levels in the experiment, straw from a pathogen-infested crop was added in varying amounts prior to seeding (Fig. 5). With the addition of 24 pounds per acre infested straw, the disease level increased 38 percent. A 55 percent infection resulted when 96 pounds per acre were added.

Winter wheat residue is not completely destroyed in open field burning nor completely buried by plowing. Consider a field with 5,000 pounds per acre of severely infested winter wheat stubble. Plowing or burning often results in burial or removal of about 95 percent of the infested residue, which greatly reduces inoculum levels and disease potential for the next winter wheat crop. However, 5 percent or 250 pounds per acre of infected straw could remain on or near the surface. This residue could potentially include infested plant crowns at or just below the soil surface, which generally are not affected by burning. As shown earlier in Fig. 2, burning of infested residue after the severe Cephalosporium stripe year of 1984 significantly reduced infection under a wheat fallow rotation, although delayed seeding of the 1986 crop without burning resulted in a similar reduction.

Using longer crop rotations, delayed seeding dates, planting more tolerant varieties, and controlling volunteer winter wheat and host winter annual grassy weeds overwinter and throughout the rotation can reduce the potential for pathogen infection in the next wheat crop without deep plowing or stubble burning after an infected crop. Following is a brief summary of the effects of different tillage and residue management options after harvest of an infested crop, and where these options might be used.

Intensive Tillage on Land That is Not Highly Erodible – Numerous research trials have shown that moldboard plowing to completely bury infested crop residue to a depth of several inches after harvest can effectively reduce the carryover of inoculum that can affect the next winter wheat crop. However, secondary tillage in the fall or spring can return some of the infested residue to or near the soil surface, permitting spore production during the fall and potential root infection during the winter and spring. This level of intensive tillage and the need to keep residue buried would restrict the use of this management option on highly erodible land.

However, growers could consider varying the intensity of tillage within fields that have varying levels of disease and susceptibility to soil erosion. For example, plowing could be used on the bottomland areas, which have high disease levels and residue production, and low erosion potential. Conservation tillage could be used to retain more surface residue on steeper slopes and hilltops, which have lower disease levels and residue production, and are highly erodible.

Stubble Burning on Land That is Not Highly Erodible – As with deep moldboard plowing, stubble burning can significantly reduce the amount of infested stubble. Stubble burning is not recommended in highly erodible fields or portions of fields because it leaves the land more vulnerable to erosion. Consequently, it has only limited application to this region. However, as with the variable tillage approach, selective burning of portions of fields that are not highly erodible and have high disease levels could be part of the disease management strategy. Burning should be avoided on highly erodible areas, such as upper slopes and ridgetops, that typically have lower disease levels and lower residue production. Reduced water storage overwinter and further reduction of soil organic matter content are impacts of field burning which also need to be considered.

Practices on Highly Erodible Land – On highly erodible land, growers need to utilize conservation tillage practices that preserve sufficient crop residue for erosion control to meet or exceed the requirements of their farm conservation plans. Using applicable control strategies listed under the preceding section on “Management of Cephalosporium Stripe in Conservation Tillage” can provide effective control of Cephalosporium stripe under conservation tillage systems.

The concept of variable tillage and residue management within fields (briefly discussed above) has considerable application to management strategies for control of diseases, weeds and other pests in fields with highly erodible land. Another approach involves varying the intensity of tillage with the crop rotation. Because of variations in residue production, disease levels and erosion potential under different crops in the rotation, most growers use a “tillage rotation” along with the crop rotation as part of their farm conservation plan. For example, consider a 3-year rotation of winter wheat-spring grain-legume or fallow. A conventional or minimum tillage system could be used to seed the spring grain following the winter wheat crop to speed decomposition of the winter wheat residue if it was infested with Cephalosporium stripe. Primary tillage after winter wheat could include the moldboard plow if used for uphill plowing or in a way that maintained sufficient surface residue. Overwinter erosion potential after a winter wheat crop is generally low due to the dry soil profile and high residue levels. The second rotation crop (such as a spring legume) could be seeded with minimum tillage into the spring grain residue. Winter wheat could then be seeded with minimum tillage or no-till after the legume. If fallow is used instead of a second rotation crop, tillage practices would need to maintain the optimal amount of spring grain residue through winter wheat seeding to conserve water and control erosion.

Where feasible, use of a tillage rotation sequence along with crop rotation would reduce carryover of Cephalosporium stripe inoculum, and reduce root injury and infection potential in winter wheat. In addition, this would also help control the critical, overwinter soil erosion in seeded winter wheat fields. In the Northwest, the most severe erosion problem occurs where winter wheat is seeded late into a residue-free, finely-tilled seedbed. Therefore, the most important tillage-residue management consideration for erosion control is during the fall and winter when winter wheat is established. Minimum or no-till seeding of winter wheat into non-host crop residue, regardless of rotation, could reduce infection potential by reducing root injury.

Summary

To control Cephalosporium stripe in conservation tillage systems, growers need an integrated management approach utilizing all feasible control options including: crop rotations with two years out of winter cereals, more tolerant varieties, delayed seeding dates, and control of volunteer winter wheat and host grassy weeds over winter. Although deep plowing or burning of infested residue can effectively reduce inoculum carryover, these practices should be considered only on cropland areas or portions of fields that are not highly erodible. Management options to reduce Cephalosporium stripe infection can be equally effective in minimizing disease potential in the next winter wheat crop as tillage and residue management practices to reduce inoculum carryover in infested residue.

Pacific Northwest Conservation Tillage Handbook Series publications are produced jointly by University of Idaho Cooperative Extension System, Oregon State University Extension Service and Washington State University Cooperative Extension.

*Roger Veseth, WSU/UI Extension Conservation Tillage Specialist, Moscow, ID;
Baird Miller, WSU Extension Agronomist, Pullman, WA;
Stephen Guy, UI Extension Crop Management Specialist, Moscow, ID;
Don Wysocki,OSU Extension Soil Scientist, Pendleton, OR;
Timothy Murray, WSU Plant Pathologist, Pullman, WA;
Richard Smiley,OSU Plant Pathologist, Pendleton;
Maury Wiese, UI Plant Pathologist, Moscow, ID.