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

WASHINGTON D.C., 20460



OFFICE OF

PREVENTION, PESTICIDES AND TOXIC SUBSTANCES

DRAFT MEMORANDUM

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

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

		Biological Analysis Branch

		Jin Kim, 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: March 14, 2007

Summary

Metam sodium is the predominant fumigant used in onion production with
the majority of usage concentrated in the Northwestern States of
Washington and Oregon followed by California.  The use is driven largely
by soil-borne pests (mainly fungi, nematodes and insects) that can not
be commercially controlled using foliar pesticides. The use of metam
sodium for the control of these pests could significantly increase
yields with an incremental benefit to growers as much as $3,361 per
acre.  Fumigation with dichloropropene plus chloropicrin would be as
effective as metam sodium in controlling these pests, but this
alternative control option is slightly more expensive than metam sodium
by $34 per acre for storage onion production in Washington and Oregon.
There are approximately 165 thousand acres of onion grown in the U.S.
annually (Agricultural Statistics 2005) and metam-sodium is applied to
about 11% or 18 thousand acres (EPA proprietary data 2002-2004).  Use of
fumigants on onion production provides benefits to growers as much as
$3,361 per acre or $83 million for 15% of the 165 thousand acres where
soil fumigants are applied.  

Statement of Purpose

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 in the production of onions.  

Background

The two major categories of onions are spring/summer varieties and
storage varieties. Both types can be yellow, white, and red. The
spring/summer varieties with mild flavor are fragile and have shorter
shelf life, while the storage varieties which are harvested during the
late summer and fall comprise 75% of the U.S. onion market. Storage
varieties are suitable for storage and processing for up to 8 months
(USDA/ERS, 2003).

China (31%), India (10%), and the U.S. (6%) are the leading producers of
onions.  From 2002 to 2004, the U.S. produced on an average of 74
million cwt of onions with a farm value of about $870 million
(Agricultural Statistics 2005).  California (28%) is the top U.S.
producer of onions followed by Oregon (15%), Washington (13%), Idaho
(7%), and Colorado (6%).  Average annual acreage, production and value
for major production states for spring/summer onions are shown in Table
1 and Table 2 for storage onions.

From 2001 to 2003, exports were on average 6.6 million cwt and 6.3
million cwt for imports. The majority of onion imports come from Mexico,
Canada, and Peru, while U.S. exports mainly to Canada, Japan, and Mexico
(USDA/ERS, 2003).

Table 1. Spring/summer onion acreage, production and value, 2002-2004
average

States	Harvested

Acres	Production

(1,000 cwt)	Yield per acre

(cwt)	Price Per cwt

California	14,267	7,272	510	$15.33

Texas	15,533	5,045	325	$25.50

Georgia	12,833	2,465	192	$30.00

New Mexico	7,600	4,097	539	$13.07

U.S. Total*	56,367	22,098	392	$19.07

Source: Agricultural Statistics 2005

*U.S. total is the sum of California, Texas, Georgia, New Mexico, and
all other spring/summer onion production states.

Table 2. Storage onion acreage, production and value, 2002-2004 average

States	Harvested

Acres	Production

(1,000 cwt)	Yield

(cwt)	Price Per cwt

California	30,567	12,939	423	$7.57

Washington	18,333	10,453	570	$11.58

Oregon	16,867	11,573	686	$8.59

New York	12,467	3,840	308	$12.73

Colorado	10,533	4,532	430	$13.87

U.S. Total*	108,768	52,634	484	$9.86

Source: Agricultural Statistics 2005

* U.S. total is the sum of California, Washington, Oregon, New York,
Colorado, and all other storage onion production states.

Fumigant Use

USDA National Agricultural Statistics Service (NASS) has surveyed
fumigants use on onions in 2002 and 2004. NASS shows that on average 9%,
5%, and 3% of acreage of onion production in the U.S. were treated with
metam sodium, dichloropropene, and chloropicrin, respectively.
Dichloropropene is predominantly used in combination with chloropicrin
(Telone C-17). Table 3 shows fumigants usage on onions during 2002-2004.
It is worth noting that the two sources, NASS and EPA proprietary data,
are divergent to each other on fumigant usage on onions.  In this
assessment, we have reviewed each of the sources carefully and have used
what we concluded to be the most appropriate and accurate information.

Table 3. Fumigant usage on onions, 2002 - 2004

Chemical	Percent Crop Treated@	Number of Application	a.i. per
application (lb/ac)	Total a.i. 

(1,000 lb/year)

Metam Sodium	9% (11%)*	1.0 	135(159)	1788 (2830)

Dichloropropene	5% (4%)	1.0 	175 (140)	1098(764)

Chloropicrin	3% (4%)	1.0 	39 (61)	177(353)

Source: National Agricultural Statistics Service (NASS), 2002 and 2004;
EPA proprietary data, 2002-2004.

@Dichloropropene and chloropricin usage are likely to be on the same
acres because dichloropropene is mostly used in combination with
chloropricin (Telone C-17). 

*Numbers in parenthesis are from EPA proprietary data 2002-2004.

EPA proprietary data shows metam sodium, dichloropropene, and
chloropicrin usage on onions by state. More than 50 percent of acres in
Washington was treated with metam sodium, while acres treated with metam
sodium (24%) and chloropicrin (14.1%) together account for about 38% of
the acres of storage onion production in Oregon. The usage of fumigants
in California is relatively low. In California, percent crop treated
with metam sodium is about 7%, and less than 2% with dichloropropene and
chloropicrin, respectively. EPA proprietary data shows lower
dichloropropene and chloropicrin usage in Oregon than those reported by
NASS in 2002 and 2004. Table 4 shows metam sodium usage on onions by
state in 2002 -2004.

Table 4. Fumigants usage on onions by state, 2002-2004

States	Active Ingredient	Percent Crop Treated	Number of Application	a.i.
per application (lb/ac)	Total a.i. 

(1,000 lb/year)

Washington	Metam sodium	53%

 (64%)*	1.0	153 

(127)*	1,508 (1,393)*

	Dichloropropene	7%	1.0	105	97

	Chloropicrin	5%	1.0	22	21

Oregon	Metam sodium	24% 

(11%)*	1.0	113 

(130)*	589 

(258)*

	Dichloropropene	7% 

(23%)*	1.0	161 

(184)	184 

(875)*

	Chloropicrin	14% (23%)*	1.0	34 

(39)*	39 

(167)*

California	Metam sodium	7%	1.0	220	713

	Dichloropropene	1%	1.0	58	36

	Chloropicrin	1%	1.0	12	8

Source: EPA proprietary data, 2002-2004; NASS, 2002 and 2004

*Numbers in parenthesis are from NASS in 2002 and 2004.

Table 5 provides information characterizing typical fumigant use in
onion production.

Table 5.  Fumigant Application Information Onion Grown In California,
Oregon, and Washington

	Metam Sodium	Chloropicrin

Application Rate 	

(lb ai/acre)	

	113 to 220 pounds per acre	22 to 34 pounds per acre



Acres Treated per Day	33 to 40 acres per tractor	33 to 40 acres per
tractor

Time of Fumigation	March - April	March - April

Application Method	Primarily shank injected in the soil	Primarily shank
injected in the soil

Strip Application	Primarily strip application	Primarily strip
application

Tarps or Water Caps	Roller to compact and seal the soil	Roller to
compact and seal the soil

Source: EPA proprietary data, 2002-2004; Personal communication with Dan
McGrath, Linn County, Oregon agricultural extension officer, 2007

Target Pests

There are many fungal, nematode and other pests affecting onion
production. We will focus on pests controlled by fumigants in major
onion producing areas in Washington and Oregon (Crop Profile for Onions,
1999,   HYPERLINK
"http://www.ipmcenters.org/cropprofiles/docs/waonions.html" 
http://www.ipmcenters.org/cropprofiles/docs/waonions.html ).

Fungi

Pink Root (Phoma terrestris)

Pink root is caused by the fungus Phoma terrestris. This soil-borne
fungus is common in most production areas. The disease may appear either
in young seedlings or later in the growing season (Pelter et al., 1992).
Infected onion roots die as the disease progresses. Reduction of the
root system decreases bulb size. 

Chemical control: Fungicides are not effective in controlling pink root.
Soil fumigation effectively reduces pink root disease and fall
fumigation is more effective than spring. The most commonly used soil
fumigant is metam sodium (Vapam at rates of 100 gallons product/A;
Sectagon at rates of 75 gallons product/A) has provided some control.
1,3-dichloropropene plus chloropicrin (Telone C-17) may be used in some
instances at a rate of 17.1 gallons product/broadcast acre.

Cultural Control: A crop rotation of three or more years between onion
crops generally suppresses this organism. Since the fungus has a fairly
broad host range, pink root may be present in fields never planted to
onions. Corn is also a good host. Many commercially available cultivars
have some pink root resistance. 

Yield loss: Up to 50% in severely affected fields (Crop Profile for
Onions, 1999,   HYPERLINK
"http://cipm.ncsu.edu/cropprofiles/docs/nyonions.html" 
http://cipm.ncsu.edu/cropprofiles/docs/nyonions.html ).

Fusarium Basal Rot (Fusarium oxysporum)

Fusarium basal rot causes occasional losses in Washington onions.
Fusarium oxysporum, the organism that causes the disease, invades roots
and as it progresses toward the bulb causes leaves to wilt and die.
Typically, the disease becomes noticeable at mid-season or later as
soils warm. Roots on infected plants eventually die and the bulb base
shows a brown discoloration. In severe cases the entire bulb base may be
rotted along with the bulb interior leaving only a hollow shell of outer
scales.

Bulb tissue infection may not be evident when the crop is placed into
storage, but later appears as a semi-watery decay developing from the
bulb base. Infection is often associated with pink root, maggots, or
insect injury (Pacific Northwest Plant Disease Control Handbook. 2002.
Oregon State University.).

Chemical Control: Fungicides do not suppress Fusarium basal rot in
onions. Results with soil fumigants for control have been erratic.

Cultural Control: Resistance is available in some cultivars. A crop
rotation of 3 to 4 years or more is practiced to help manage this
disease.

Yield loss: Up to 50% in severely affected fields (Crop Profile for
Onions, 1999,   HYPERLINK
"http://cipm.ncsu.edu/cropprofiles/docs/nyonions.html" 
http://cipm.ncsu.edu/cropprofiles/docs/nyonions.html ).

White Rot (Sclerotium cepivorum)

White rot, caused by Sclerotium cepivorum, is a devastating disease of
onions that causes infected plants to wilt and die (Pelter et al.,
1992). Outer leaves decline first. Typical symptoms include bulb rot
covered with a white cottony growth in which tiny black sclerotia are
embedded. The disease may persist in the soil for as long as 25 years.
Chemical and cultural control practices have little effect once the
disease is introduced. White rot is spread by contaminated bulbs or
transplants of any member of the onion family or on contaminated bins,
vehicles, or tillage equipment. It is not spread by seed. 

A Washington State Department of Agriculture quarantine to limit
movement of white rot into Adams, Franklin and Grant counties from
contaminated areas has been adopted. This quarantine prohibits importing
bulbs, transplants, or other vegetative material for propagation unless
the materials are certified free of white rot by the state department of
agriculture in which the material originated. Agricultural equipment,
vehicles, or bins used in other onion areas must be sterilized before
being brought into the quarantine area. 

Chemical Control: Growers do not generally use chemicals to control
white rot. Soil fumigation using metam sodium (Vapam at rates of 100
gallons product/A; Sectagon at rates of 75 gallons product/A) has
provided some control. Under most conditions, even the best chemicals
control only a portion of the disease and soils become useless for
production of onions and other Allium spp.

Cultural Control: In Washington, growers use sanitation to avoid
introducing white rot via contaminated soil carried on equipment or
other means. Growers plant only disease-free transplants. Exclusion is
the best way to control white rot. Once this disease is established in a
field, it is very difficult to grow any Allium spp. successfully. 

Nematodes

Nematodes are recognized as a problem more by large-scale growers than
by small scale-growers. Onion crops in Washington are occasionally
attacked by stubby-root and, in some small areas, by stem and bulb
nematodes. Root knot nematodes can cause stand and yield reductions but
are generally managed by crop rotation and/or soil fumigation for
disease control.

Stubby-Root Nematode (Paratrichodorus allius and P. minor)

The most important nematode pest of onions in Washington is the
stubby-root nematode, Paratrichodorus allius and P. minor. Stubby-root
nematodes affect a wide range of plant species and are particular
problems in very sandy soils with grasses or cereals in the crop
rotation. Roots of onions attacked by the stubby-root nematode are
extremely short with a yellow to brownish cast and plants become
stunted. 

Chemical Control: Metam sodium fumigation of soil reduces nematode
populations in the soil. 1,3-dichloropropene (Telone II at a rate of 18
gallons product/broadcast acre) and oxamyl (Vydate L at 2 gallons
product/banded acre) are the most common treatments for stubby-root
nematodes. In Oregon, stubby-root nematodes are controlled by fumigating
soils with 1,3-dichlorpropene (Telone) (Pacific Northwest Plant Disease
Control Handbook, 1999).

Cultural Control: Crop rotation is the primary cultural control method
used by onion growers. In particular, growers try to avoid following
mint, which is a host for the stubby-root nematode.

Yield loss: Up to 50% in severely affected fields (Crop Profile for
Onions, 1999,   HYPERLINK
"http://cipm.ncsu.edu/cropprofiles/docs/nyonions.html" 
http://cipm.ncsu.edu/cropprofiles/docs/nyonions.html ).

Insect Pests

Thrips and maggots are the most serious insect pests of onions in
Washington State. Thrips, both onion thrips and western flower thrips
are an increasing problem for many growers in the Columbia Basin. Onion
maggots are particularly troublesome in western Washington and seed corn
maggots damage crops in the Columbia Basin. Aphids, armyworms, and
cutworms, leafhoppers, leafminers, and wireworms are occasional pests. 

Wireworms (Limonius spp.)

Wireworms, Limonius spp., are the elongated, glossy yellow to red-brown
larvae of click beetles. They range in length from 3/8 to 1 inch (6).
They complete their juvenile stages in the soil, where they feed on
plant tissue for 2 to 5 years. Affected plants may have a wilted
appearance and damage commonly occurs in patches of the field. These
insects, if present in high numbers, can eliminate portions of onion
stands. 

Chemical Control: Soil fumigation is effective against wireworms,
especially when populations are high. Several insecticides, including
diazinon, are registered for control, but must be applied prior to
planting and are generally not used. 

Cultural Control: Crop rotation is a useful management tool used by
growers. Alfalfa, if kept free of weeds, can be particularly helpful in
reducing wireworm populations.

Weed Pests

Metam sodium, a fumigant used for suppression of some diseases, also
controls some weeds and can reduce the need for herbicides. 

Chemical Control Alternatives

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 in to 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 ITC 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. We did not find
much literature on the control of onion soil-borne diseases using
biofumigation. The results of a study documents that metam sodium
significantly reduced mycorrhizae colonization of onion roots and had no
affect on onion yield (Beck et al., 2004). In contrast, biofumigants did
not significantly affect mycorrhizae colonization or pink root
infection, but tended to reduce onion yields. This yield reduction was
probably due to poorer onion stands that were seen each year of the
study. Plant residue from biofumigant incorporation may have caused
trash to build up on the planter shoes or reduce soil-seed contact,
thereby reducing germination (Beck et al., 2004). Biofumigation has
warranted further investigation into the use of mustard green manures
for control of soilborne pests in potato and other cropping systems
(McGuire, 2003).  

Benefits of Soil Fumigation

Our assessment focuses on onion production in California and Washington.
California is the most important production state for both spring/summer
and storage onions. Washington is included in this assessment because it
is the second leading producer of storage onions and metam sodium is
widely used on over 50% of onion production acreage.  Oregon is another
important production state for storage onions with more than 38% of
acres treated with metam sodium or chloropicrin.  However, crop budget
information which is necessary for the economic impact assessment is not
available for Oregon.  We anticipate that our findings will be generally
relevant to all U.S. onion production where fumigants are widely used.

It is documented that several onion pest are each capable of causing up
to 50 percent yield losses if the pest pressure was severe (Crop Profile
for Onions in New York, 1999) and no fumigant was used.  No information
is available on the actual percent yield loss (caused by individual pest
or collectively) without the use of metam sodium (mainly used against
fungi and nematodes), dichloropropene (effective against nematodes),
chloropicrin (effective agsinst fungi) or a combination of
dichloropropene and chloropicrin in onion growing areas (New York,
Washington, Oregon and California). For the purpose of this analysis we
assumed that it is highly unlikely that in a given growing season the
pest pressure of every pest will be severe. Therefore, we made an
assumption that the likely maximum yield losses without the use of above
cited fumigant may be up to 50% in a given growing season. We also
believe that if metam sodium is not available to the growers, they will
use dichloropropene plus chloropicrin for the control of soil borne
pests (fungi and nematodes) and the yield losses using this mixture will
be negligible.

In the following section we evaluate the economic benefits of soil
fumigation to onion producers in California and Washington.  BEAD uses a
partial budget analysis to estimate the impacts of changes in
production.  That is, we evaluate the consequences on a typical acre of
the crop grown, rather than attempt to assess the impacts in the context
of a whole enterprise, which could include multiple crops under
cultivation.  This approach allows the Agency to compare losses to net
operating revenue, which is defined as the difference between gross
revenue and variable operating costs, on a per-acre basis.  The analysis
ignores fixed costs, which are highly dependent on land ownership and
the size and diversity of the grower’s operation, and therefore
difficult to define on a per-acre basis.  Estimated impacts if soil
fumigants could not be used in California and Washington onion
production are summarized in Tables 6, and 7.  

California

Table 6.  Estimated Per Acre Gross Revenue, Operating Costs, and Net
Operating Revenue Impacts for California Spring/summer Onion Production

	Baseline

Metam-sodium	Alternative

Dichloropropene + Chloropicrin	% Change	No Fumigants available*	% Change

Yield (cwt/acre)	510	510	0%	255	-50%

Price  ($/cwt)	$16	$16	0%	$16	0%

Gross Revenue  ($/acre)	$7,946	$7,946	0%	$3,973	-50%

Metam-sodium ($/acre)

Dichloropropene + Chloropicrin ($/acre)	$170	

$102	

-40%



Other Operating Costs  ($/acre)	$1,692	$1,692	0%	$1,692	0%

Harvest Costs  ($/acre)	$1,846	$1,846	0%	$1,846	0%

Total Operating Costs  ($/acre)	$3,813	$3,745	-1.8%	$3,538	-5.5%

Net Operating Revenue  ($/acre)	$4,133	$4,201	1.7%	$435	-90%

Source: University of California Cooperative extension (2006);
Agricultural Statistics, 2005; EPA proprietary data, 2002-2004

*1, 3 Dichloropropene alone can control nematodes, but fungi still may
cause up to 50% yield loss in a given growing season. Therefore,
economic losses when 1,3 Dichloropropene is used alone are estimated the
same as the case when no fumigants are available.

In the absence of metam-sodium, the best alternative control for
California onion producers would be dichloropropene plus chloropicrin. 
Alternative control would result in a slight increase in net operating
revenue from $4,133 to $4,201 per acre or an increase of 1.7% of net
operating revenue. This is because the cost of dichloropropene plus
chloropicrin ($102 per acre) is cheaper than that of metam sodium
($170). Without the use of any fumigants, yield losses of up to 50% may
occur in some situations with losses in net revenues over 90%, which
represents unsustainable losses to onion producers in California.  

Washington

Table 7.  Estimated Per Acre Gross Revenue, Operating Costs, and Net
Operating Revenue Impacts for Washington Storage Onion Production under
Rill Irrigation

	Baseline

Metam-sodium	Alternative

1,3 Dichloropropene + Chloropicrin	% Change	No Fumigants available*	%
Change

Yield (cwt/acre)	570	570	0%	285	-50%

Price  ($/cwt)	$12	$12	0%	$12	0%

Gross Revenue  ($/acre)	$6,572	$6,572	0%	$3,286	-50%

Metam-sodium ($/acre)

Dichloropropene + Chloropicrin ($/acre)	$123	

$157	

27.6%



Other Operating Costs  ($/acre)	$1,847	$1,847	0%	$1,848	0%

Total Operating Costs  ($/acre)	$1,970	$2,004	1.7%	$1,848	-7.8%

Net Operating Revenue  ($/acre)	$4,602	$4,568	-0.7%	$1,438	-68.5%

Source: Cooperative Extension Washington State University (1999);
Agricultural Statistics, 2005; EPA proprietary data, 2002-2004

*1, 3 Dichloropropene alone can control nematodes, but fungi still may
cause up to 50% yield loss in a given growing season. Therefore,
economic losses when 1,3 Dichloropropene is used alone are estimated the
same as the case when no fumigants are available.

Without the use of metam-sodium, the best alternative control for
Washington storage onion producers would be dichloropropene plus
chloropicrin.  The alternative control would result in a decrease in net
operating revenue from $4,602 to $4,568 per acre or a decrease of 0.7%
of net operating revenue. Unlike the case in California, the cost of
dichloropropene plus chloropicrin ($157 per acre) is higher than that of
metam sodium ($123). If no fumigant is available, yield losses of up to
50% may occur in some situations with losses in net revenues over 68%,
which represents unsustainable losses to onion producers in Washington. 


Conclusion

Based on the average onion production and soil fumigant usage
information during 2002-2004, there are approximately 165 thousand acres
of onion grown in the U.S. annually (Agricultural Statistics 2005) and
metam-sodium is applied to about 11% or 18 thousand acres (EPA
proprietary data 2002-2004).  Fumigation with dichloropropene plus
chloropicrin is as effective as metam sodium in controlling soil-borne
pests, but this alternative control option is slightly more expensive
than metam sodium by $34 per acre for storage onion production in
Washington and Oregon.  Use of fumigants on onion production in U.S.
benefits growers as much as $3,361 per acre or $83 million for 15% of
the 165 thousand acres where soil fumigants are applied.  

References

Beck, D., Geary, B., Ransom, C., Mcgonigle, T., Brown, B., Thornton, M.
2004. Biofumigation with mustard, canols and oilseed radish as an
alternative to metam sodium for control of pink root and weeds in
onions. Poster presented at the National Allium Research Conference –
Pest Management (2004).   HYPERLINK
"http://www.colostate.edu/Depts/CoopExt/TRA/Allium/Abstracts/Biofumigati
on.htm" 
http://www.colostate.edu/Depts/CoopExt/TRA/Allium/Abstracts/Biofumigatio
n.htm 

Crop Profile for Onions in New York (1999) General Production
Information   HYPERLINK
"http://cipm.ncsu.edu/cropprofiles/docs/nyonions.html" 
http://cipm.ncsu.edu/cropprofiles/docs/nyonions.html 

EPA proprietary data, 2002-2004.

McGuire, A. 2001. Using green manures in potato cropping systems.
Cooperative Extension, Washington State University.

(  HYPERLINK
"http://cru.cahe.wsu.edu/CEPublications/eb1951e/EB1951E.pdf" 
http://cru.cahe.wsu.edu/CEPublications/eb1951e/EB1951E.pdf )

Pacific Northwest Plant Disease Control Handbook; Extension Services of
Oregon State University, Washington State University, and the University
of Idaho: Corvallis, OR, 1999.

Pelter, G.Q., E.J. Sorensen, R.E. Thornton, and R. Stevens. 1992. Dry
Bulb Onion Production, Washington State University, EB 1693.

Personal communication with Dan McGrath, Linn County Agricultural
Extension Officer. Albany, Oregon.

United States Department of Agriculture (USDA) (2003). “Commodity
Highlight: Dry-bulb Onions.”    HYPERLINK
"http://www.ers.usda.gov/Briefing/Vegetables/vegpdf/OnionHigh.pdf" 
http://www.ers.usda.gov/Briefing/Vegetables/vegpdf/OnionHigh.pdf  
Economic Research Service (ERS).

USDA (2005).  “Agricultural Statistics, 2005.”    HYPERLINK
"http://www.usda.gov/nass/pubs/agstats.htm" 
http://www.usda.gov/nass/pubs/agstats.htm  National Agricultural
Statistics Service (NASS).

USDA (2003). “Vegetables and Melons Outlook.” Economic Research
Service (ERS).

USDA (2002, 2004).   HYPERLINK
"http://www.pestmanagement.info/nass/app_usage.cfm" 
http://www.pestmanagement.info/nass/app_usage.cfm 

Agricultural Chemical Use Database. NASS.

 However, there might be some reasons that make more acres treated with
metam sodium (7%) than dichloropropene plus chloropicrin (1%). For
example, growers might be more familiar with using metam sodium or there
might be the cases when dichloropropene plus chloropicrin is in fact
more efficacious than metam sodium.

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