Mustard Green Manures for Potato Production

Final Report for SW03-018

Project Type: Research and Education
Funds awarded in 2003: $45,653.00
Projected End Date: 12/31/2007
Matching Non-Federal Funds: $18,324.00
Region: Western
State: Washington
Principal Investigator:
Andrew McGuire
Washington State University Extension
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Project Information


Over the course of this project, the use of mustard green manures in Washington potato production has held steady from an estimated 23,620 acres in 2003 to 24,400 acres in the fall of 2006. However, of the farmers using this practice, only a few are doing it to replace their use of metam sodium fumigant. The majority are using the practice to 1) improve their soils and control wind erosion, 2) supplement their normal pest management practices, including fumigation. This project’s research activities, including green manure variety trials, agronomic trials with mustard, and investigation into the soil quality effects of mustard green manures, have provided valuable information to farmers. This information was disseminated to them through field days, workshops, publications and a website. The on-farm research used in this project has proven valuable in rousing farmer’s interest and helping them adopt the practice. However, there are still many questions about the practice of using mustard green manures that will not be answered through on-farm research. The nature of these questions will require a team of researchers - soil microbiologists, plant pathologists, and horticulturists – doing research at research stations, greenhouses, and laboratories where factors can be better controlled than in farmer’s fields.

Project Objectives:


Objective 1: Determine the measurable factors related to suppression or non-suppression of potato early dying in processing potatoes.

Objective 2: Determine the species and variety of mustard, or other Brassica, that will most benefit Washington potato growers.

Objective 3: Increase the adoption of mustard green manures by potato growers through an integrated program of on-farm research and education.

Performance Targets

Increasing the Producer's Knowledge Base: production of research summaries containing the results from +/- fumigant trials, wheat straw management trials, and green manure variety trials

Dissemination of Information: records of website users/hits, number of articles published, and attendance at presentations and the field day.
Number of Acres Impacted: increase acres planted to mustard green manures in Central Washington by 25% every year for the next five years (three covered by this proposal), from 9,260 acres in 2001, to 28,000 acres being planted the fall of 2006.

Actual Positive Economic Impact: if we feel that a significant number of potato growers are replacing their fumigant with mustard green manures, we will conduct a survey to estimate this impact.


Washington potato growers, although producing record yields, are experiencing reduced profits due to decreasing market prices and increasing production costs. A major part of production costs for most growers is fumigation. They also have to spend more on inputs due to the decreasing soil quality.

Washington growers are increasingly interested in growing mustard as a green manure preceding potatoes to help control of nematodes, weeds, and soil-borne diseases. This practice has the potential to replace some soil fumigation and to improve soil quality. We will conduct on-farm research aimed at reducing the risk of farmers using mustards to replace fumigation.


Materials and methods:

Objective 1.

In 2003, an on-farm trial was organized where fumigant was applied through the center-pivot irrigation system on only parts (wedges) of the field. Previously, such research had been done using ground application equipment, which made randomization and replication relatively easy. With fumigant application through the irrigation system, both randomization and replication were much more difficult, and impossible in some cases. After the 2004 yields were measured, this type of testing was abandoned as almost all farmers were applying the fumigant through their irrigation water and the one farmer who was using ground application equipment replaced his fumigant use completely with mustard green manuring.

The focus was then shifted to analyzing the changes in the soil resulting from mustard green manures. In 2004, soil samples were taken in May from 12 locations representing three conditions: fields receiving mustard green manures, neighbor fields not receiving green manures, neighboring native soils. These soils were tested for Zn, Mn, CEC, pH, organic matter, soil texture, and fluoride levels. These results were analyzed for trends and differences which led to a second round of soil sampling and testing in late summer. We took samples from five fields that were being planted to mustard green manures before 2005 potatoes, where the farmer cooperators had agreed to apply a fumigant treatment on only a portion of the field. The soil samples from these fields were tested for soil organic matter, pH, soil texture, nematode counts (for Pratylenchus sp.), active C, soil stability, soil respiration, and levels of Verticillium dahliae.

In 2005, soil samples were taken on March 3, before spring tillage, from replicated plots in three fields characterized by different soil textures (82, 49, and 31% sand) where the treatments were mustard and no mustard in 2004. These samples were analyzed for fluorescein diacetate (FDA) hydrolysis, -glucosidase, both estimates of microbial activity (FDA has been correlated with disease suppression), active C, total C and % sand, silt, and clay. We were able to observe the following potato crop in only one of these fields that with the loamy sand soil, but this did not yield any valuable information (see below).

Additional soil samples were taken from nine fields, at four locations in each field, before a mustard green manure crops were planted. Another set of samples was taken from the same locations in March, 2006, to be analyzed for various potential indicators of pest suppression: FDA, b-glucosidase, dehydrongenase, active C, pH, % sand, silt and clay, and N, C and S contents. The idea was to determine if any of these measurements correlated with disease suppression at these sites.

Of the five fields where soil samples were collected in 2004 and potatoes planted in 2005, we were able to measure potato yields on just three fields, comparing mustard with the fumigant metam sodium. Of the two missing fields, one did not receive metam sodium and the other had unrelated problems that severely affected production.

Objective 2

Variety trials were randomized with four or more replications of each entry. Trials were planted in August (see trial results for each year’s exact planting date) with a walk-behind planter and were fertilized and irrigated according to WSU recommendations. Biomass samples were taken at the end of August. Oven-dried subsamples were used to determine moisture content.
Samples taken for glucosinolate analysis were placed in mesh bags (large sand bags) and immediately placed in coolers containing dry ice. They were then transported to the lab doing the analysis the same day and placed in walk-in freezers until they could be freeze dried and prepared for analysis. Dr. Matt Morra at the University of Idaho did the glucosinolate analysis.

Objective 3

2003: A mustard green manure field day in late October attracted 78 producers, researchers, and crop consultants.

2004: The results of the variety trial, past research, and basic principles were disseminated to farmers and crop consultants at a Mustard Green Manure field day held Oct. 26th. Handouts from this event can be found at:
The field day was attended by approx. 45 people.

A website developed to disseminate information on mustard green manures received over 16,000 hits in 2004 through November. Mustard green manure publications were downloaded about 3,100 times in the same period. Through direct contact by presentations or posters, 1,324 people were made aware of the benefits and uses of mustard green manures. The results of this work were published in the Australian newsletter, Biofumigation Update, and in Potato Progress, the grower newsletter of the Washington State Potato Commission.

2005: The annual mustard green manure field day was not held this year, but was replaced with a workshop on Feb. 2, 2006. This allowed for more in-depth learning about this practice and the related topics of soil quality and biology. Twenty-nine farmers and crop consultants attended. Six other presentations were given in 2005 on mustard green manure management.

The website received over 27,609 hits from January through October, 2005. This is an 89% increase over 2004. Mustard green manure publications were downloaded about 3,745 times in the same period.

2006: A mustard green manure workshop was held on Feb. 2, 2006, in Moses Lake, Washington. It attracted 29 people and covered the basics of mustard green manure management, potential pest suppression, soil quality improvements, and potential risks.

On April 5th, a session on Potential Mechanisms of Organic Matter Mediated Pest Suppression was held at the National IPM symposium in St. Louis. I organized this session, and although it did not address mustard green manures directly, research on the mechanisms occurring with other organic soil amendments could be similar to those with the mustard. Interestingly, one researcher has found evidence that the glucosinolates in Brassicas, the biofumigation effect, may not be a major mechanism. We had been thinking similarly, which is why we had discontinued the expensive glucosinolate analysis of mustards in our variety trials.

In late June, I attended the 2nd International Biofumigation conference in Moscow, Idaho. There I facilitated a discussion among the presenters about the state of our knowledge and where we should go in the future. One important theme that evolved from this session is the need for a set of basic information and treatments in every biofumigant related experiment. This, probably more than anything else, would help move the science forward in this area. The details can be found in the well-written review, Matthiessen and Kirkegaard, 2006, Biofumigation and Enhanced Biodegradation: Opportunity and Challenge in Soilborne Pest and Disease Management, Critical Reviews in Plant Sciences, 25:235–265. If the many Pacific Northwest researchers attending this meeting adopt this paper's recommendations, it could have significant impact on the use of green manures before potatoes. This meeting also highlighted that the questions that we have about these practices will not be answered soon, but only after years of continued carefully designed experiments.

Two mustard green manure field days were held in October, 2006; one each in the Northern and Southern Columbia Basin. Total attendance was about 57, but many of them were first-timers at these field days.

The website received over 31,290 hits from January through November, 2006. This is a 5% increase over 2005. Mustard green manure publications were downloaded about 2,993 times in the same period, a reduced number from 2005. This reflects either the cooling interest among farmers from past years (those that want to know about this may have already educated themselves) and/or the remaining number of farmers interested in practice but not yet using it is decreasing.

A current partial budget analysis was posted online comparing mustard green manures to metam sodium fumigation.

Research results and discussion:

Objective 1

In the analysis of the 2005 soil samples, the levels of FDA, b-glucosidase, and active C were significantly higher in the mustard plots in the silt loam, but no significant differences were found in the loamy sand or sandy loam. All three measurements were correlated to total soil C, with correlations following this pattern: FDA>active C>-glucosidase. -glucosidase and active C were highly correlated to each other.
In the three potato fields harvested in 2005, there were no significant treatment differences when they were considered as individual replicates. This lack of differences did not allow us to correlate previous soil measurements with the success or failure of mustard as a replacement for metam sodium.

The analysis of the soil samples collected before and after mustard green manures on nine fields was delayed due to the departure of the soil technician who was originally going to do the work. We had difficulty finding someone else to do the work and even when we did, they were not able to do the work quickly. Because of this delay, we were not able to do further soils work. Furthermore, when the analysis data did come back from the laboratory doing the work (early 2007) we discovered that they had analyzed only one set of samples and had apparently lost the second set of samples. This loss eliminated any information that could be gained from these soil sampling efforts.

Objective 2

Variety trials were conducted in the fall of 2003, 2004, 2005, and 2006. Complete results are posted on the website at

In 2004 the variety trial had 18 varieties of two mustard species and another trial comparing six non-mustard Brassica crops. Samples of all the mustard varieties were taken and sent to a laboratory for analysis of glucosinolate concentrations.

In 2005, we conducted an early planted (July 12) variety trial of nine entries (replicated, mustard and other species) and five unreplicated plots of high and low dhurrrin sorghums to compare with the mustards. Buckwheat and proso millet were found to be much more competitive and productive than mustard, or sorghum, when planted in July and grown into September at this location. However, several grain sorghums hold potential for the planting window.

A later planted variety trial (Aug. 12) contained 11 varieties of mustard, both B. juncea and S. alba, arrugula, broccoli, oilseed radish, Typhon (turnip x rape cross), and winter and spring canola varieties. Some varieties from the early trial were also planted in this later trial but did not produce well.
Most of the mustard plots lodged during a heavy rain and were not harvestable. Plots of the remaining entries were harvested for yield estimates, but no significant differences were found. Yields from Brassica species in the later planted trials and those from buckwheat and proso millet of the early planted trial were similar. In 2005, we opted to not analyze glucosinolate levels from this year’s trial as it would not have yielded further useful information.

In trying to determine what significant differences might exist between cover crop species which produce differences in disease suppression in the field (Neeno-Eckwall et al, 2001) we measured whole plant brix levels in various variety trial entries. We found some differences, with differences generally arranged: grasses>Brassicas>buckwheat. The Brassica entries did not differ from each other. Data can be found at the website mentioned above.

In 2006, we conducted an early variety trial (July 12 planting) with 10 entries including sudangrasses, teff, mustard, arrugula and turnip. A heavy downpour just after planting decreased or eliminated the broadleaf's emergence and those plots were abandoned. The grass entries however did much better and biomass samples were taken on Sept. 8, analyzed and the results posted on the green manure website. The varieties of sudangrass that were replicated (we had limited seed for some entries as they are experimental) yielded significantly more biomass than the teff.

We also conducted a late variety trial (August 12 planting) with 18 entries of two species of mustards, mustard blends, arugula, arugula/mustard blends and oilseed radish, all with 4+ replicates. The arugula did not emerge well in most of the plots, or in the surrounding field, and so it was not harvested. The mustard, however, did well, and 4 replications of each entry were harvested on Oct. 18th. The data obtained showed that in a year with good growing conditions, many of the mustard varieties tested can produce high amounts of biomass. In agreement with past trials, the variety that bloomed first, Ida Gold, produced less biomass, although all the differences were not statistically significant. 3.5 tons/ac of dry biomass seems to be a target that growers should aim for with August planted mustard green manures.

Research conclusions:

Objective 1

Most of the impact of the work comparing mustard green manures to the fumigant metam sodium came before or just as this project started. It was in this period that we were working with farmers who applied the fumigant with ground application equipment. When the project started, those farmers had either completely replaced their fumigation with mustard or had other problems that eliminated their field for on-farm research. So, we started working with farmers who apply their fumigant through the center-pivot irrigation systems. We found that this made it much more difficult, or even impossible, to conduct our on-farm research on these fields without introducing confounding factors. This is why we eventually gave up this activity and did not make the advances that we sought at the beginning of the project.

Objective 2

We have extensively tested mustard varieties, both those commercially available and experimental, and have identified those that work well in this system. Commercial seed companies have used this data to select the varieties that they sell and also the price at which they are sold. Mustard from the Columbia Basin of Washington is now being sold for green manure use throughout the West and even in states in the Midwest and Eastern United States.
A WSU nematologist is now working extensively with green manures, including mustards and arugula, to suppress pest nematodes in conjunction with nematicides. This probably would not have occurred without this ongoing mustard project and without the documentation of a significant number of farmers using mustard green manures, as this work was opposed by some Washington State Potato Commission board members.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

Professional articles, refereed

Collins, H., Alva A., Boydston R., Cochran R., Hamm P., McGuire A., & Riga E. (2006). Soil microbial, fungal, and nematode responses to soil fumigation. Biology and Fertility of Soils, 42, 247-257.

Grunwald, N., Collins, H., & McGuire A. (2006). Control of Fusarium root rot with a mustard green manure, 2003. Biological and Cultural Tests for Control of Plant Diseases: B & C Tests 21.

McGuire, A.M. (2003). Mustard green manures replace fumigant and improve infiltration in potato cropping system. Crop Management. Online: doi:10.1094/CM-2003-0822-01-RS.

Riga E., Mojtahedi H., Ingham R. E., & McGuire A.M. (2003). Green manure amendments and management of root knot nematodes on potato in the Pacific Northwest of USA. Nematology Monographs and Perspectives, 2, 151-158.

Professional articles, non-refereed

McGuire, A.M. (2003, June). Green manuring with mustard: Improving an old technology. Agrichemical and Environmental News, 206, 13 pp.


McGuire, A.M. (2003). Mustard green manures replace metam sodium in potato cropping system. Biofumigation: A Possible Alternative to Methyl Bromide, Abstract Book. Research Institute for Industrial Crops, Bologna, Italy.

Extension Publications - State

McGuire, A.M. (2006). Cover crops for the Columbia Basin: Mustard. Revision of WSU Publication EB1952E, 3 pp.

McGuire, A., Mora M., & Brown J. (2006). Biofumigation Symposium roundtable discussion summary,

Trade Journals, Grower Newsletters

“Soil’s Important Ecosystem Needs Careful Attention-Washington green manure research continues,” Potato Grower, January 2005.

“Mustard Green Manure Incorporation Methods and Timing,” Potato Progress, Sept. 28, 2004, Vol. 4:14. Washington State Potato Commission.

“Planning to Plant Mustard, Consider Direct Seeding,” Potato Progress, June 30, 2004, Vol. 4:10. Washington State Potato Commission.

“Mustard Green Manures Yield Multiple Benefits in USA Potato Crops,” Biofumigation Update, May 2004, No. 19.

“Planting dates for mustard green manures,” Potato Progress, Aug. 4, 2003, Vol. 3:11. Washington State Potato Commission.

“Green manuring with mustard: Improving an old technology,” (modified from Agrichemical and Environmental News paper), Tilth Producers Quarterly, a Journal of Organic and Sustainable Agriculture, 2003, Vol. 12:3, 5 pp.

“Green manuring with mustard: Improving an old technology,” (modified from Agrichemical and Environmental News paper), Sustaining the Pacific Northwest, June 2003, Vol. 1:3, 4 pp.

“Mustard brings back old farming practice,” Basin Business Journal, May 30, 2003.


McGuire, A.M. 2003-2006. Mustard green manures.

McGuire, A.M. 2004. Managing soilborne pests with green manures; an online forum. Webpage linked to online forum archives, to be expanded as resource and contact source for the 57 forum participants.



Mustard Green Manures Replace Metam Sodium in Potato Cropping System 4/1/04 First International Biofumigation Symposium, Florence, Italy

Invited, Regional

Considerations for green manure use when drafting canola production regulations 10/17/06
WSDA Listening Session, Yakima, WA.

Benefits and Mechanisms of Mustard Green Manures in Potato Production 7/20/04
Green Manures Workshop, Ft. Hall, ID.

Management of Mustard Green Manures for Pest Control and Soil Quality 2/27/04
Western Washington Potato Conference, Mt. Vernon, WA

Mustard Green Manures in Potato Cropping Systems 2/18/04
Putting Biology to Work on your Vegetable Farm, Canby, OR

Mustard Green Manures for Potato Production 2/28/03
Western Washington Potato Conference, Mt. Vernon, WA

Mustard Green Manures for Potato Production 2/12/03
San Luis Valley Potato/Grain Conference, Monte Vista, CO

Mustard Green Manures for Potato Production 1/27/03
Oregon Potato Conference, Ontario, OR


Mustard Green Manures; Knowns, Unknowns, and Potential 12/5/03
Farm Fair, Hermiston, OR


Investigation of the use of mustard green manures for wind erosion control 12/14/05
Researchers, farmers and government personnel

Mustard Green Manures for Soilborne Pest Suppression 10/22/05
WSU Cropping Systems class field tour

Mustard Green Manures for Soilborne Pest Suppression 10/4/05
EPA administrators field tour

Mustard Green Manures for Potato Production 2/16/05
Wilbur Ellis Growers Meeting

Managing Green Manures for Soilborne Pest Control 2/4/05
Warden Conservation District annual meeting

Why grow cover crops? 1/25/05
Cenex Harvest States Growers Meeting

Mustard Green Manure; Potential in Seed Crop Rotations 1/20/04
Columbia Basin Vegetable Seed Association Annual Meeting

The Role of Organic Matter and Mustard Green Manures in Building Soil Health 2/17/04
Inter-County Weed District #52 Meeting


Mustard Green Manures for Soilborne Pest Suppression in Potatoes 9/14/06 WSU Pike Place Market Event

Managing Soilborne Pests with Mustards 4/1/05 WSU Celebrating Excellence Showcase

The Online Forum: a Tool for Developing Integrated Agricultural Systems 11/1-11/3/04 Annual Meeting of the American Society of Agronomy, CSA, & SSSA, Indianapolis, IN

Mustard Green Manure Use in Washington State, USA 3/31-4/1/04 First International Biofumigation Symposium, Florence, Italy

Outreach Events Organized

Mustard Green Manure field days 9/25-9/26/06
2nd International Biofumigation Symposium 6/26-6/29/06
Potential Mechanisms of Organic Matter Mediated Soilborne Pest Suppression seminar at National IPM conference 4/5/06

Mustard Green Manure Workshop 2/2/06
Mustard Green Manure Field Day 10/26/04
Managing Soilborne Pests with Green Manures; An Online Forum 2/23-3/8/04
Mustard Green Manure Field Day 10/23/03

Education and Outreach Outcomes

Recommendations for education and outreach:

Areas needing additional study

  • The mechanisms related to use of mustard green manures that affect specific pests, such as Verticillium dahliae and root-knot nematodes
    The role of glucosinolates, if any, in pest suppression in the field

    The soil factors that affect the effectiveness of pest suppression by mustard green manures

    The soil properties that are changed by long- and short-term use of mustard green manures

    The amount of biomass that is needed to be effective

    The environmental factors that affect the practice’s effectiveness, such as soil temperature at incorporation and the timing of incorporation in relation to planting the following crop

    The nutrient cycling after long- and short-term use of mustard green manures

    The use of mixtures of mustards and other Brassicas for green manures

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.