  SEQ CHAPTER \h \r 1 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460



OFFICE OF

PREVENTION, PESTICIDES AND TOXIC SUBSTANCES

MEMORANDUM

SUBJECT:	Assessment of the Benefits of Soil Fumigation with Metam-sodium
in Potato Production (DP # 337490)

FROM:	Tara Chandgoyal, Ph.D., Plant Pathologist

		 Biological Analysis Branch

		Derek Berwald, Ph.D., Economist	

Economic Analysis Branch

Biological and Economic Analysis Division (7503P)

THRU:	Arnet Jones, Chief 	

Biological Analysis Branch

Tim Kiely, Chief

Economic Analysis Branch

Biological and Economic Analysis Division (7503P)

TO:		John Leahy, Senior Policy Advisor

Special Review and Reregistration Division (7508P)

PRODUCT REVIEW PANEL: February 15, 2007

Summary

Metam sodium is the predominant fumigant used in potato production with
most usage concentrated in the Northwestern States (Idaho, Washington
and Oregon) followed by the Upper Midwest States (Michigan, Minnesota,
and Wisconsin) and California.  The value of potato production in the US
is about $2.9 billion, with about $1.3 billion in the Pacific Northwest,
and about $240 million in California.  The use is driven largely by
Verticillium wilt (a soil borne fungal disease) and plant parasitic
nematodes. Although there are registered alternatives to metam-sodium
(such as 1,3-dichloropropene for the control of nematodes and
chloropicrin for the control of the Verticillium fungal pathogen), these
alternatives do not provide efficient control of this soil-borne
pathogen. The benefits of using metam-sodium rather than the
alternatives are substantial, both in terms of yield increases and lower
costs.  It has been experimentally demonstrated that the growers are
likely to experience a 13 percent lower yields using a combination of
1,3-dichloropropene and chloropicrin over metam sodium.  If we consider
the benefits of metam-sodium relative to no fumigants at all, the yield
benefits are even greater.  The use of metam-sodium prevents the fungal
inoculums building up in the soil after several years of partial
control.  In areas with high pest pressure, only metam-sodium enables to
continue producing potatoes.  Overall, the annual benefits of
metam-sodium are estimated to be about $800 per acre in California, and
about $250 per acre in the Pacific Northwest, which translates to
benefits of about $8 million per year in California, and about $48
million per year in the Pacific Northwest.    

Background

As part of the Reregistration Eligibility Decision (RED) process, EPA is
assessing the risks and benefits of the use of several soil fumigants:
dazomet, chloropicrin, metam potassium, metam sodium, and methyl
bromide.  This document presents the assessment of the benefits provided
by the soil fumigants, particularly metam sodium, in the production of
potatoes.  Conceptually, the benefits of a pesticide like a soil
fumigant are the improvements in production and/or reductions in cost
resulting from the pesticide’s use.  The social benefits of a
pesticide are divided between the users of the pesticide, e.g., potato
producers, and consumers of potatoes and potato products.  Consumers
benefit because higher production and/or lower costs translate into a
cheaper and more abundant supply of potatoes.

This assessment compares the current situation in which fumigants are
available for use, subject to existing label restrictions, to the
situation that is estimated to occur if the fumigants were not
available.  

Potatoes

Potatoes are grown commercially throughout the country but the
Northwestern States of Idaho, Washington and Oregon have 555,220 acres
of planted potatoes, representing 45% of United States acreage. Forty
five percent of U.S. production of potatoes is produced in these three
states with a value of $1.3 billion per year (USDA NASS; Table 1).  This
analysis will focus on potato production in the Pacific Northwest states
of Idaho, Oregon and Washington; the Upper Midwest States of Michigan,
Minnesota, and Wisconsin; and California.  Table 1 shows acreage, yield,
production and value for these regions, as well as the United States as
a whole. 

Potato producers use fumigants in their production to control pests. 
This analysis focuses on the benefits of fumigation with metam sodium,
and the use of metam sodium and other fumigants are given in Table 2,
which shows the percent crop treated, the acreage treated, the amount of
active ingredient applied and the application rates for chloropicrin,
dichloropropene, metam potassium and metam sodium.  Florida is also
shown in that table, to contrast fumigant use in that state with the
ones in this analysis; metam sodium is much less important to growers in
that state.

 Table 1.  Potato Acreage, Production and Value, 2001 – 2005 Average.

Region	Planted Acres	Harvested Acres	Production

(1000 cwt.)	Yield

(cwt./acre)	Value

($1000)	Price

($/cwt.)

California	42,160	42,100	16,067	381	237,828	14.86 

Pacific Northwest 1	555,220	552,600	240,932	379	1,269,660	5.40 

Upper Midwest 2	177,300	172,160	64,071	378	418,235	6.61 

U.S.	1,224,300	1,197,840	446,725	374	2,870,658	6.45 

Source:  USDA NASS Quickstats database.

1Idaho, Oregon, and Washington.

2Michigan, Minnesota and Wisconsin.



Table 2.  Fumigant Use on Potato, 2001-2005 Average.

Region	Percent

of Planted

Acres

 Treated	Acres Treated	Total Pounds of Active Ingredient Applied	Rate

(Pounds per Acre per Year)

Chloropicrin





California	0.7%	280	12,890	47

Pacific Northwest 1	2.7%	14,800	346,470	34

Upper Midwest 2	0.2%	390	1,860	5

Florida	6.4%	2,120	87,660	31

U.S.	1.5%	17,920	454,510	34

Dichloropropene





California	1.1%	480	58,090	141

Pacific Northwest 1	13.6%	75,740	10,240,710	146

Upper Midwest 2	0.2%	420	12,990	97

Florida	32.2%	10,640	666,650	64

U.S.	7.3%	89,920	11,326,920	124

Metam Potassium





California	0.3%	140	18,283	128

Pacific Northwest 1	1.0%	5,280	662,391	132

Upper Midwest 2	N/A	 N/A	N/A	N/A

Florida	9.2%	3,030	261,943	94

U.S.	0.7%	8,460	942,617	116

Metam Sodium





California	23.6%	9,930	1,524,550	143

Pacific Northwest 1	34.6%	192,040	25,310,500	136

Upper Midwest 2	11.8%	20,890	3,141,000	147

Florida	7.7%	2,540	178,070	74

U.S.	18.5%	226,400	30,306,690	141

Source:  EPA Proprietary Data

1Idaho, Oregon, and Washington.

2Michigan, Minnesota and Wisconsin.



Target Pests

Verticillium wilt: It is a major factor limiting tuber yield in many
potato production areas throughout the United States (Powelson and Rowe.
1993; Rowe, 1986). The pathogen can persist in the soil for many years
and the yield losses caused by Verticillium wilt vary from year to year
and with location and environmental conditions. The most severe symptoms
and yield losses happen when the plants are stressed by poor irrigation
and poor fertilization (Rowe, 1987). The fungal inoculum remains viable
for many years in the soils and quickly builds up when potatoes are
planted.

Nematodes: Root knot (Meloidogyne spp.), Stubby-Root Nematode
(Paratrichodorus teres) Golden nematode (Globodera rostochiensis) and
some others. These nematodes are soilborne root parasites that are
capable of causing significant quantitative and qualitative damage to
roots and tubers. Stubby root nematodes also can serve as vectors for
corky ringspot disease, which causes qualitative damage to the tuber
rendering them unmarketable.

Pest Control

Soil fumigation of fields with metam sodium is conducted from late
August to November and the potato crop is planted the following spring
in the Pacific Northwest and Upper Mid-Western States. In lower
California, the soils are fumigated in October/November and the potato
crop is planted in December/January. Metam sodium fumigation effectively
controls Verticillium wilt (Powelson, and Rowe, 1993) and nematode
populations.  Metam sodium is typically applied through sprinkler
irrigation and/or central pivot irrigation. Metam sodium decomposes to
methylisothiocyanate (MITC) gas that moves throughout the soil and kills
fungal mycelium and nematodes. Metam sodium may also be applied as a
shank soil injection treatment.  Metam sodium applications do not
completely eradicate the Verticillium fungus from the soil. Economically
damaging populations of Verticillium usually develop after 1-2 potato
crop cycles (Gianessi, et al., 2002). Therefore, most growers will
usually fumigate their fields every growing season.

Metam sodium also reduces nematode populations below economic threshold
levels. Some growers use 1,3-dichloropropene (1,3-D) alone or a mixture
of 1,3-D and chloropicrin in some of their fields having high to very
high populations of nematodes (National Potato Council, 2006). However,
1,3-D alone or its combination with chloropicrin is not as effective as
metam sodium alone in controlling Verticillium wilt disease (Hamm,
1993). 

Yield Losses

National Potato Council claims that without the use of metam sodium the
growers are likely to incur approximately 10% yield losses. Hamm (1993)
showed that the growers are likely to lose 13% yield using Telone C-17
instead of metam sodium. He also demonstrated that yield losses of 50%
may occur without the use of fumigants in potato production. Additional
published information shows that metam sodium when applied to soil
through sprinkler irrigation prior to planting increases yields by
23-33% (O’Sullivan and Reyes, 1980; Powelson and Hamm, 2002). This
will translate into 19-25% losses if metam sodium is not available to
growers. In another study it has been documented that the growers are
likely to lose 9.0-16.8% of total yield without the use of metam sodium
(Hamm and Hane, 1997).

Field Sizes and Planting Season

 In the Pacific Northwest the typical potato field size varies between
120-160 acres and upper mid-west 30-50 acres (National Potato Council,
2006). The data on field size in California and Florida are not
available. 

Alternatives

Fungal Resistance: Commercially grown cultivars of potatoes are
susceptible to the disease and nematode pests. There are reports that
some genetically modified varieties have resistance against Verticillium
but none are commercially available at the present time. 

OtherPesticides: The fungal pathogen and nematodes are soil-borne
organisms. Fumigants (such as metam sodium and/or combination of 1,3-D
and chloropicrin) are effective in controlling these pests. The National
Potato Council claims (2006) that chloropicrin is not a viable option
because chloropicrin has no activity against nematodes, is difficult to
apply, has lower efficacy against Verticillium pathogen and is more
expensive than metam sodium. If 1,3-D and chloropicrin are combined the
yield losses can be minimized to about 10-13% (Hamm, 1993). However, it
is unknown whether the losses caused by Verticillium fungus will
increase in the following crop seasons. This fungus has the tendency to
build up in the soil if not controlled effectively.  

Biofumigation: This term is used to describe the effects of Brassica
rotation crops or green manures on soilborne pests (McGuire, 2001).
Brassica crops such as rapeseed and mustard contain biologically active
chemicals, called glucosinolates. In the soil, certain glucosinolates in
the roots of rotation crops, or in the roots, stems and leaves of green
manures, break down into isothiocynates (ITCs) and other chemicals. ITCs
are known to kill or suppress some soilborne disease pathogens,
nematodes, and weed seeds. There are many types of glucosinolates, some
of which produce different types of ITCs, which vary in their toxicity
to different pests. Methyl isothiocynate is the active chemical produced
when metam sodium, a common synthetic fumigant, is applied to the soil;
hence the name biofumigation when ITCs are produced by plants. In the
Pacific Northwest, the US-EPA has funded a project to study the
replacement of metam sodium use with green manure cropping in potato
production (Strategic Ag. Initiative Project, 2005) for the control of
soilborne nematode, wireworm and weed control. At present it is unknown
whether biofumigation will effectively control the same pests as
controlled by metam sodium. Based on available information, we believe
that biofumigation may suppress fungal inoculum and nematode populations
in the soil. However, it appears that biofumigation is neither a
commercially feasible nor an economically viable alternative to metam
sodium fumigation of soil for potato production.  In the Pacific
Northwestern and upper Mid-Western states, the growers fumigate their
fields in the late fall so that the potato crop may be planted quickly
in the coming spring season. Therefore, if the growers shall decide to
biofumigate their fields in the coming spring season then they may also
lose early and mid-growing season of potatoes. A recent study concluded
that biofumigation has promise and warrants further study into the use
of mustard green manures for control of soilborne pests in potato and
other cropping systems (McGuire, 2003).

Benefits of Metam-sodium 

No Alternative Fumigants 

If growers do not use other fumigants to replace metam sodium, the
primary impact will come from reduced yields in response to increased
disease.  Potato is a valuable crop and decreased yield can result in
large reductions in grower income.  For this analysis, we assume that
yield losses due to disease without metam sodium control would be 22%,
the midpoint of the 19 – 25% range estimated by O’Sullivan and Reyes
(1980) and Powelson and Hamm (2002).  Note that this estimate is much
lower than the 50% yield loss estimated by Hamm (1993).  If that
estimate were correct, losses would be correspondingly higher.  

In Tables 3 and 4, we present rough estimates of the impacts to growers
who could not use metam sodium.  The yield and price data are from the
USDA National Agricultural Statistics Service, and they represent the
average yield and price for California, the acreage weighted average
price and yield for the states that make up the Pacific Northwest
(Idaho, Oregon, and Washington).  The cost of using metam sodium is the
acreage-weighted average from EPA proprietary data.  The other operating
costs are based on information in the cost and return estimates for
Idaho (used for the Pacific Northwest), and California.  The harvest
cost of $352 for the Pacific Northwest baseline is reported in the Idaho
cost and returns report.  Because we anticipate yield changes, it is
inappropriate to assume that harvest costs will not change.  To estimate
the harvest cost with the lower yield, we calculate the harvest cost per
hundredweight from the baseline ($0.93 per hundredweight), and apply
that to the lower yield.  More problematic is that the California cost
of production study does not include harvest costs.  For that reason, we
use the same harvest cost per hundredweight, and apply it to the
California yield to calculate estimated harvest costs.  This is a crude
estimate, but alternative data are not available. 

Table 3: Change in Gross Revenue, Operating Costs, and Net Operating
Revenue for Potato Production, California and Pacific Northwest

	California

Pacific Northwest

	Baseline	Without Metam Sodium	Change	% Change

Baseline	Without Metam Sodium	Change	% Change

Yield (cwt./acre)	381	297	-84	-22%

379	295	-83	-22%

Price ($/cwt.)	15	15



5	5



Gross Revenue  ($/acre)	5,662	4,416	-1,246	-22%

1,967	1,534	-433	-22%

Cost of metam sodium ($/acre)	130



	106



	Other Operating Costs  ($/acre)	914	914



1,063	1,063



Harvest Costs ($/acre)	355	277



352	275



Total Operating Costs  ($/acre)	1,399	1,191	-208	-15%

1,521	1,338	-183	-12%

Net Operating Revenue  ($/acre)	4,263	3,225	-1,037	-24%

447	197	-250	-56%

Source:  USDA NASS; EPA Proprietary Data; Patterson, Seyedbagheri, and
Smathers (2005); Mayberry, 2000.

Note: this table assumes that metam sodium is not replaced with another
fumigant.



A 22% reduction in yield for the Pacific Northwest results in yield
falling from 379 hundredweight per acre to 295 per acre.  At an average
price of $5 per hundredweight, gross revenue per acre will be reduced by
$433.  Net operating revenue will be reduced by only $250 per acre,
because of the cost savings to growers, who face lower harvest costs and
no longer pay for metam sodium.  The $250 per acre reduction in net
operating revenue represents a reduction of about 56%, relative to the
baseline where metam sodium is used.  In California, the impacts on
yield are similar, a loss of about 84 hundredweight per acre.  The
impact on gross revenue, however, is larger (about $1,250) because
California potatoes receive a higher price.  We estimate the change in
net operating revenue for California to be about -24%, or a loss of over
$1,000 per acre.  

For the Upper Midwest (Michigan, Minnesota, and Wisconsin) and the
United States overall, no reasonable cost data were available.  For
these areas, we present estimated changes in revenue that result from a
decrease in yield of 22% in Table 4.  In both cases, estimated gross
revenue is expected to fall by over $500 per acre.   

Table 4: Change in Gross Revenue for Potato Production, United States
and Upper Midwest

	Upper Midwest

United States

	Baseline	Without Metam Sodium	Change

Baseline	Without Metam Sodium	Change

Yield (cwt./acre)	378	295	-83

374	291	-82

Price ($/cwt.)	7	7

	6	6

	Gross Revenue  ($/acre)	2,485	1,939	-547

2,411	1,881	-530

Cost of metam sodium ($/acre)	122



118



Source:  USDA NASS; EPA Proprietary Data.



Using 1,3-D and chloropicrin to replace metam sodium

Growers who replace metam sodium with a combination of chloropicrin and
1,3-D will face smaller yield reductions than those who choose not to
fumigate.  However, the cost of the new treatments will be higher than
metam sodium.  There is little data on the actual cost of 1,3-D and
chloropicrin applied to potatoes because there is not much of this use. 
Hamm (1993), found a yield reduction of 13% without metam sodium, when
treated with Telone C17 at 27.5 gallons per acre.  Based on a cost of
Telone C17 of about $10 per gallon (EPA Proprietary Data), we assume a
cost per acre of $275 in this analysis.  

The impact of using 1,3-D and chloropicrin in place of metam sodium is
shown in Table 5.  In this case, growers face lower yield losses (we
assume 13%) without metam sodium, but must also pay for the alternative,
which is more expensive than metam sodium.  In California, the smaller
yield reductions make up for the increased costs of 1,3-D and
chloropicrin; losses to growers are smaller than the previous scenario,
where they do not replace metam sodium with another fumigant.  Losses
are still high, however, at approximately $835 per acre, or a decrease
of about 20% in net operating revenue.  

In the Pacific Northwest, however, we estimate that the additional cost
of 1,3-D and chloropicrin erases the advantage of reduced yield losses
due to lower price received as compared to California.  We estimate net
operating revenue in the Pacific Northwest to fall by almost $380 with
1,3-D and chloropicrin in place of metam sodium, a decrease of about
85%.  It in unlikely that most growers would find this a better choice
than using no fumigant at all to replace metam sodium, unless increased
disease pressure over time reduces yields even further.  We do not
report additional results in this scenario for the Upper Midwest or the
US overall, due to the lack of information on operating costs, but we
note that the yield per acre and price received are more similar to the
Pacific Northwest figures than those for California. 

Table 5: Change in Gross Revenue, Operating Costs, and Net Operating
Revenue for Potato Production, California and Pacific Northwest with
1,3-D Plus Chloropicrin Replacing Metam Sodium

	California

Pacific Northwest

	Baseline With Metam Sodium	Without Metam Sodium	Change	% Change

Baseline With Metam Sodium	Without Metam Sodium	Change	% Change

Yield (cwt./acre)	381	331	-50	-13%

379	329	-49	-13%

Price ($/cwt.)	15	15



5	5



Gross Revenue  ($/acre)	5,662	4,926	-736	-13%

1,967	1,712	-256	-13%

Cost of Metam Sodium ($/acre)	130



	106



	Cost of 1,3-D Plus Chloropicrin ($/acre)1

275



	275



Other Operating Costs  ($/acre)	914	914



1,063	1,063



Harvest Costs ($/acre)	355	309



352	307



Total Operating Costs  ($/acre)	1,399	1,498	99	7%

1,521	1,644	124	8%

Net Operating Revenue  ($/acre)	4,263	3,428	-835	-20%

447	67	-379	-85%

Source:  USDA NASS; EPA Proprietary Data; Patterson, Seyedbagheri, and
Smathers (2005); Mayberry, 2000.

1  Data were insufficient to estimate the cost of the appropriate
combination of 1,3-D plus chloropicrin based on current use for potato. 
Instead, the rate of 27.5 gallons per acre used by Hamm (1993) was
multiplied by an estimated cost of $10 per gallon, based on EPA
Proprietary Data.  



There are important uncertainties with this analysis.  The cost data are
representative of a region, but do not necessarily represent average
costs of production.  Regional variation in production methods, pest
pressure, and agronomic conditions can be large, but we make no attempt
at a rigorous evaluation of those issues here.  Most importantly there
is great uncertainty about the medium- and long-run response by growers
to the disease.  Fungal diseases like Verticillium wilt may become more
of a problem over time, but that is not included in the analysis.  We
assume for this document that growers respond by accepting reduced
yields, but in fact they may also change rotation patterns, apply a mix
of other chemicals to control disease, or end potato production
altogether as disease pressure increases.  

Conclusion

Metam sodium is the predominant fumigant used in potato production with
most usage concentrated in the Northwestern States (Idaho, Washington
and Oregon) followed by the Upper Midwest States (Michigan, Minnesota,
and Wisconsin) and California.  The use is driven largely by
Verticillium wilt (a soil borne fungal disease) and plant parasitic
nematodes. Although there are registered alternatives to metam-sodium
(such as 1,3-dichloropropene for the control of nematodes and
chloropicrin for the control of the Verticillium fungal pathogen), these
alternatives do not provide efficient control of this soil-borne
pathogen. The benefits of using metam-sodium rather than the
alternatives are substantial, both in terms of yield increases and lower
costs.  It has been experimentally demonstrated that the growers are
likely to experience a 13 percent lower yields using a combination of
1,3-dichloropropene and chloropicrin over metam sodium.  If we consider
the benefits of metam-sodium relative to no fumigants at all, the yield
benefits are even greater.  The use of metam-sodium prevents the fungal
inoculums building up in the soil after several years of partial
control.  In areas with high pest pressure, only metam-sodium enables to
continue producing potatoes.  Overall, the annual benefits of
metam-sodium are estimated to be about $800 per acre in California, and
about $250 per acre in the Pacific Northwest, which translates to
benefits of about $8 million per year in California, and about $48
million per year in the Pacific Northwest.    

REFERENCES

EPA Proprietary Data.  EPA proprietary data are data on pesticide use
purchased from private sector firms.

Gianessi, L. P. Silvers, C.S., Sankula, S and Carpenter, J.E. 2002.
Plant biotechnology: Current and potential impact for improving pest
management in U. S. Agriculture-An analysis of 40 case studies. Fungal
resistant poatoes. Published by National Center for Food and
Agricultural Policy, 1616 P Street NW, Washington DC 20036).

Hamm, P. B. 1993. Soil fumigation and soil borne diseases of potato.
Paper presented at the 1993 Washington State Potato Conference and Trade
Fair, Pages 87-93. A photocopy of this document was sent by Andrew
Jensen (National Potato Council, 2006) to Tara Chandgoyal via email on
01-25-2007. 

Hamm, P. B and Hane, D. 1997. Soil fumigation and impact on yield in
early, mid and late season cultivars. Progress Report to the Agri. Res.
Foundation, Oregon Potato Commission.   HYPERLINK
"http://oregonstate.edu/potatoes/reports/1997/page053.pdf" 
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Mayberry, Keith S.  Sample Cost to Establish and Produce Potatoes:
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"http://www.agecon.ucdavis.edu/outreach/cost_return_articles/potatoes.pd
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McGuire, A. 2001. Using green manures in potato cropping systems.
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"http://cru.cahe.wsu.edu/CEPublications/eb1951e/EB1951E.pdf" 
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McGuire, A.M. 2003. Mustard green manures replace fumigant and improve
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(http://www.plantmanagementnetwork.org/pub/cm/research/2003/mustard/)

National Potato Council. 2006. A meeting of National Potato Council and
growers with the representatives of US-EPA (SRRD and BEAD divisions) on
the use and efficacy of fumigants in potato cultivation. Meeting was
held on December 4, 2006, at Potomac Yard building (2770 South Crystal
Dr), Arlington, VA 22202.

O’Sullivan John and Andres A. Reyes. 1980. Effects of soil fumigation,
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Patterson, Paul E,, Mir-M. Seyedbagheri, and Robert L. Smathers. 2005
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HYPERLINK "http://www.ag.uidaho.edu/aers/PDF/Crops/EBB2-Po1-05.pdf" 
http://www.ag.uidaho.edu/aers/PDF/Crops/EBB2-Po1-05.pdf   

Patterson, Paul E and Robert L. Smathers. 1999. Crop Input Cost Summary
for Idaho, University of Idaho. A. E. Extension Series No. 00-04,
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Powelson and Hamm. 2002.   HYPERLINK
"http://www.ncfap.org/40CaseStudies/OnePagers/PotatoFROnePager.pdf" 
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Powelson, M.L. and R.C. Rowe. 1993. Biology and management of early
dying of potatoes. Annual Review of Phytopathology 31: 111-126

United States Department of Agriculture, National Agricultural
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"http://www.nass.usda.gov/QuickStats/indexbysubject.jsp?Pass_group=Crops
+%26+Plants" 
http://www.nass.usda.gov/QuickStats/indexbysubject.jsp?Pass_group=Crops+
%26+Plants .

Rowe, R.C. 1986. Managing potato production for optimal plant health.
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Rowe, R.C. 1987. Potato early dying: causal agents and management
strategies. Plant Disaease 71:482-489

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with green manure cropping production” funded by the United States
Environmental Protection Agency.

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