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The Importance of Soil Fumigation: Forest Seedlings
June 2013
Janet Carpenter
Crop Protection Research Institute
CropLife Foundation
1156 15th Street, NW #400 Washington, DC 20005
Phone 202-296-1585 www.croplifefoundation.org Fax 202-463-0474
Key Points
The benefits of soil fumigation for forest tree seedling production extend beyond the
nursery to the millions of acres of forests that depend on healthy seedlings for their
establishment.
Without soil fumigants, forest tree nursery producers would experience lower yields and
decreased seedling quality and potentially spread pathogens, diseases, weeds and other
soilborne pests into newly planted forest areas.
Losses of up to 100% are possible if pest free certification cannot be met due to
inadequate pest control.
Technical Summary
In 1999, over 1.6 billion forest tree seedlings were produced in the United States, including
conifer and hardwood seedlings that are used for reforestation, forest establishment, fiber
production, Christmas tree production, wildlife habitat and conservation purposes (Table 1).
More recent production estimates for the southern US estimate that 832 million seedlings were
produced for planting in the 2010/11 season, 96% of which were conifers (Tables 2 and 3). In
the state-owned nurseries of the Northeast, 65 million seedlings were available for planting in
Spring 2010, 69% confiners and 27% hardwoods (Table 4). More recent production estimates
are currently being collected for the western US. The total production area was estimated at 127,
220 acres between 2001 and 2003 [1]. Nurseries are owned and managed by federal, state, local
government and private entities.
Maintaining pest-free nursery soils is critical to the production of healthy seedlings. Soil
fumigation has been used in bareroot forest nurseries to control pathogens, nematodes, insects
and weeds for many decades [3]. Target pests of fumigants used in forest seedling nurseries are
shown in Table 5.
Damping-off, caused by numerous fungi (e.g. Fusarium spp., Rhizoctonia solani, Pythium spp.),
is probably the most widespread disease of forest tree nursery stock [7]. The term refers to a
group of symptoms which may occur at different stages of plant growth. Pre-emergence
damping-off refers to a decayed seed or a seedling that is killed prior to emergence from the soil.
Post-emergence damping-off occurs after seedlings appear above the ground, generally attacking
at or slightly above the soil line. During long periods of high humidity, the tops of seedlings
may be attacked, which is referred to as top damping-off [7].
Root rot is also caused by a number of fungi. Black root-rot is one of the most serious root rots,
especially in southern nurseries, caused by a complex of organisms including Sclerotium
bataticola and Fusarium spp. [7].
Nematodes, microscopic animals that feed on the roots of plants, can cause severe plant damage,
especially to small seedlings. Typical symptoms of nematode injury include a general decline,
stunting and chlorosis. Nematode damage to roots can result in attack by soil fungi, which
together may cause significant damage [7].
Weeds not only compete with seedlings for nutrients, light and water, but some weed species
such as yellow nutsedge (Cyperus esculentus L.) are considered quarantine pests in some
states[4].
It is estimated that 2% of US forest seedling production area is fumigated each year [1]. This
figure understates the importance of fumigants in forest seedling production, as the efficacy of
fumigants allows for less frequent fumigation, typically every 3 or 4 years for conifer species to
produce two or three crops per fumigation cycle. For hardwood seedling production, fumigation
is more frequent because hardwood species are more susceptible to diseases controlled by
fumigation than conifers [2].
A 1993 a survey of nurseries that produce bareroot tree seedlings indicated that 86% of the
nurseries fumigated in preparation for planting to control soilborne diseases, insects, nematodes
and weeds. In the South, 96% reported reliance on fumigation and in the North and West, about
80% of the nurseries reported using soil fumigation. At least 80% of nurseries reporting the use
of fumigants were using methyl bromide [5]. In 1995, 95% of southern nursery managers
surveyed reported using fumigants. The most important pest problems reported were nutsedge
and post-emergence damping-off [6].
Methyl bromide is the most commonly used fumigant in forest tree nurseries. In the southeast,
all seedling production area is fumigated with methyl bromide [16]. In the northeast,
approximately 80% of nursery acreage is fumigated with methyl bromide, and less than 10% of
nursery acreage is fumigated with metam-sodium or dazomet [14]. Some of the nurseries in
northern states like Minnesota or on the Upper Peninsula of Michigan do not fumigate due to low
pest pressure [14].
The production of forest tree seedlings is subject to pest free certification standards to prevent
the spread of plant pests and diseases. All states have certification standards [10] and, in
addition, all nurseries have additional internal quality control standards. Many of the state
standards indicate fumigation of seedling planting beds prior to seeding with methyl bromide as
the preferred method of treatment (e.g. Georgia, Texas, Mississippi, Tennessee, Louisiana,
Oklahoma, North Carolina, Alabama, Oregon and Indiana) [16].
Since 2005, forest tree nursery managers have continued to use methyl bromide under the critical
use and quarantine and preshipment exemptions to the phaseout under the Montreal Protocol.
By 2013, all use of methyl bromide in forest tree nurseries will fall under the quarantine and
preshipment exemption. Table 6 shows the historical use of methyl bromide based on
applications for methyl bromide critical use exemptions.
Since the phaseout of methyl bromide was announced in 1991, research into alternatives to
methyl bromide has been a priority for the forest nursery industry. In a 1994 review of 36
published reports of research conducted over 40 years on the effect of methyl bromide on
seedling number and size, non-fumigated beds produced 33% fewer seedlings than those
fumigated with methyl bromide or methyl bromide in combination with chloropicrin [17]. Non-
fumigated beds produced 27% fewer seedlings than metam sodium treatments, which were the
second best among widely tested fumigants in terms of average performance [17]. (See Table 7.)
In a 1994 study comparing hot water treatment, 1,3-D and metam-sodium/chloropicrin to
standard methyl bromide fumigation, the hot water treatment improved seedling production
compared to the untreated control (Table 8). The number of pathogenic nematode counts at the
end of the trial were higher in the hot water treated beds than any other treatment, but the
differences were not statistically significant (Table 9). At the time of the study, hot water
treatment was deemed impractical due to the slow rate of treatment relative to the scale of forest
tree nursery production areas [13].
In field trials at a forest nursery in Washington, comparing conventional methyl bromide-
chloropicrin application to reduced rate alternative fumigant treatments and a nonfumigated
treatment in Douglas-fir seedling production, weeding time was over 20 times higher for the
nonfumigated than for all fumigant treatments [4]. The percentage of seedlings culled from the
nonfumigated plots averaged across three nurseries was 12% compared to 7-8% for fumigated
treatments based on operational grading [4].
As of October 2011, researchers studying methyl bromide alternatives for southern forest tree
nurseries have identified the top three alternatives as: Pic + (85% chloropicrin & 15% solvent
A); Chloropicrin (100%); and DMDS & Chloropicrin (dimethyl disulfide & 21% chloropicrin)
[8].
Estimated Impacts
Without soil fumigants, forest tree nursery producers would experience lower yields and
decreased seedling quality and spread pathogens, diseases, weeds and other soilborne pests into
newly planted forest areas. The EPA states that “maintaining pest-free nursery soils is critical to
producing healthy seedlings and the foundation for establishing economically viable forests” [3].
Given pest free certification standards, if growers no longer used fumigants and did not use any
alternative pest control practices, it is estimated that losses would be up to 100% due to the lack
of marketable stocks. The total benefits of fumigants with no alternative pest control practices
would be $42.6 million for the Southern US and $19.6 million for State Owned Nurseries in the
Northeast in terms of total revenue.
Given the limited amount of research on non-fumigant alternatives for forest tree seedling
production, we estimate that using the best non-fumigant alternative, forest tree seedling
producers would experience yield decreases of 33%, based on the compiled results presented in
the 1994 review [17]. Growers would save the current cost of fumigation. Estimated impacts on
forest tree seedling production are presented in Tables 11-14 for the Southern US and the state-
owned nurseries in the Northeastern US. For the Southern US, total benefits are estimated at
$12.2 million and for State Owned Nurseries in the Northeast total benefits are estimated at $4.5
million. This estimate understates the benefits of fumigants to the extent that it does not take
into account the costs of an alternative program. However, a 33% yield loss may be an upper
bound, as this is the estimated yield loss with no fumigation and no alternative treatment, as there
was no research into non-fumigant alternatives.
References
1. US Department of State, 2007, USA CUN09 SOIL FOREST SEEDLING NURSERIES
Open Field, http://www.epa.gov/ozone/mbr/cun2009/cun2009_Seedling.pdf.
2. US Environmental Protection Agency, 2007, Memorandum: Assessment of Benefits of
Soil Fumigants (Methyl Bromide, Chloropicrin, Metam-Socium, Dazomet) Used by
Forest Tree Seedling Nurseries, April 20.
3. Haase, Diane L., 2009, “The Latest on Soil Fumigation in Bareroot Forest Nurseries,”
Forest Nursery Notes, Summer, pp. 22-25.
4. Weiland, Jerry E., Leon, Anna L., Edmonds, Robert L., Littke, Willis R., Browning, John
E., Davis, Anne, Beck, Bryan R., Miller, Timothy W., Cherry, Marilyn L. and Rose,
Robin, 2011, “The effects of methyl bromide alternatives on soil and seedling pathogen
populations, weeds, and seedling morphology in Oregon and Washington forest
nurseries,” Canadian Journal of Forest Research, vol. 41, no. 9, pp. 1885-1896.
5. Smith, Richard S. Jr. and Fraedrich, Stephen W., 1993, “Back to the Future—Pest
Management Without Methyl Bromide,” Tree Planters’ Notes, vol. 44, no. 3, pp. 87-90.
6. Cram, Michelle M. and Fraedrich, Stephen W., 1996, “Survey of Southern Forest
Nurseries: Fumigation Practices and Pest Management Concerns. In: Landis, T.D.; South,
D. B., tech. coords. National Proceedings, Forest and Conservation Nursery Associations.
Gen. Tech. Rep. PNW-GTR-389. Portland, OR: USDA Forest Service, Pacific Northwest
Research Station: 19-27.
7. Hodges, Charles, S. Jr., 1962, Diseases in Southeastern Forest Nurseries and their
control, USDA Forest Service, Asheville, North Carolina, Station Paper No. 142.
8. Jackson, Paul, Starkey, Tom and Enebak, Scott, 2011, “Five Years of Methyl Bromide
Alternatives Research in Southern Forest Tree Nurseries,” Methyl Bromide Alternatives
Outreach Conference.
9. Enebak, S.A., Starkey, T.E., and Quicke, M., 2011, “Effect of methyl bromide
alternatives on seedling quality, nematodes and pathogenic soil fungi at the Jesup and
Glennville Nurseries in Georgia: 2007 to 2008,” Journal of Horticulture and Forestry,
vol. 3, no. 5, pp. 150-158.
10. National Plant Board, Laws and Regulations,
http://www.nationalplantboard.org/laws/index.html
11. Enebak, Scott A., 2011, “Update on Soil Fumigation: MBr Alternatives and
Reregistration Decisions,” USDA Forest Service Proceedings RMRS-P-65, pp. 40-45.
12. Enebak, Scott A., 2011, “Forest Tree Seedling Production in the Southern United States
for the 2010-2011 Planting Season,” Southern Forest Nursery Management Cooperative,
Technical Note 11-01.
13. Carey, William, 1997, “A Single Nursery Test of Hot Water, 1,3-D, and Metham-Sodium
as Alternatives to Methyl Bromide,” Southern Forest Nursery Management Cooperative,
Research Report 97-7.
14. Ron Overton, 2012, Personal Communication, USDA Forest Service, Northeastern Area,
West Lafayette, Indiana.
15. US Forest Service, Tree Planting in the U.S., http://www.rngr.net/resources/tpus.
16. Scott Enebak, 2012, Personal Communication, Auburn University Southern Forest
Nursery Management Cooperative, Auburn, Alabama.
17. Bill Carey and Ken McNabb, 1996, “The Loss of Methyl Bromide as a Fumigant in
Forest Tree Nurseries and the Impact on Reforestation Programs,” Auburn University
Southern Forest Nursery Management Cooperative Technical Note 96-2.
18. US Department of State, 2010, USA CUN12 Soil Forest Seedling Nurseries Open Field,
http://www.epa.gov/ozone/mbr/2012_nomination.html.
Photo Credits:
Top left: Southern Forest Nursery Management Cooperative, An Example of the Effect of
Chloropicrin in New Zealand, https://nurserycoop.auburn.edu/images/nzchlor.jpg
Top right: Southern Forest Nursery Management Cooperative, An Example of Chloropicrin at a
Southern Pine Nursery, https://nurserycoop.auburn.edu/images/chloropic.jpg
Bottom left: Southern Forest Nursery Management Cooperative, Effects of Stunt Nematode
Bottom right: Scott Enebak, Auburn University, Fumigant Trials in Wisconsin, showing poor
emergence in alternative treatments
Table 1. Forest Tree Nursery Production by State in 1999
State
Trees
(1,000)
GA 251,362
AL 236,625
FL 160,045
TX 125,900
AR 120,000
NC 104,000
SC 99,438
OR 86,801
WA 84,812
LA 67,078
Other 277,026
US TOTAL 1,613,087
Includes production by federal, state, and local government, forest industry and other industry
ownership.
Source: [15]
Table 2. Conifer Seedling Production in the Southern US by State for the 2010-2011
Planting Season (x1000)
Bareroot
Conifers
Container-
grown
Conifers
Total
Conifers
AL 69,555 5,800 75,455
AR 80,314 0 80,314
FL 24,544 16,507 41,051
GA 153,330 62,247 215,577
LA 19.337 298 19,635
MS 79,419 7,200 86,619
NC 40,515 11,310 51,825
OK 3,732 11 3,743
SC 103,969 1,655 105,624
TN 4,700 0 4,700
TX 89,078 1 89,079
VA 25,770 0 25,770
Total 694,363 105,029 799,392
Source: [12]
Table 3. Hardwood Seedling Production in the Southern US by State for the 2010-2011
Planting Season (x 1000)
Bareroot
Hardwoods
Container-
grown
Hardwoods
Total
Hardwoods
AL 960 0 960
AR 6,767 0 6,767
FL 4,341 0 4,341
GA 5,524 2,422 7,946
LA 3,226 0 3,226
MS 820 76 896
NC 1,194 0 1,194
OK 1,133 0 1,133
SC 4,256 0 4,256
TN 1,387 0 1,387
TX 59 3 62
VA 805 0 805
Total 30,472 2,501 32,973
Source: [12]
Table 4. State-owned nursery production available for shipment in Spring 2010 for
Northeast States (x 1000)
State
Conifer
Seedlings
Hardwood
Seedlings
Deciduous
Shrub
Seedlings
Total
Seedlings
IL 298 1,583 129 2,010
IN 546 2,846 127 3,519
IA 131 1,047 230 1,409
KY 379 2,439 184 3,002
MD 1,705 1,082 188 2,976
MI 6,664 0 0 6,664
MN 9,992 1,102 16 11,109
MO 1,182 2,556 840 4,579
NH 225 54 56 335
NJ 285 143 34 462
NY 732 294 190 1,216
OH 0 0 0 0
PA 1,360 997 447 2,804
WI 20,945 3,140 187 24,272
WV 250 554 55 859
TOTALS 44,694 17,838 2,683 65,215
Source: [14]
Table 5. Target pests for soil fumigants in forest seedling nurseries
Category Key Pests
Pathogens Fusarium, Macrophomina, Rhozoctonia, Pythium, Phytophthora, Phoma,
Botrytis, Cylindrocladium
Weeds Cyperus spp., Inula brittanica, Oxalis stricta, Cirsium arvense, Rorippa
sylvestris; other broadleaves and grasses
Nematodes Circonemoides spp., Helicotylenchus spp.
Source: [1]
Table 6. Critical Use Exemption Applicants’ Reported Historical Use of Methyl Bromide (Acres Treated)
Applicant 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Southern Forest Nursery Management Cooperative NA NA NA 1,620 1,620 1,620 1,620 1,620 1,625 1,625
International Paper 343 217 457 299 282 249 316 324 161 257
Illinois Department of Natural Resources 37 37 42 40 32 40 37 37 0 0
Weyerhaeuser-South 156 158 178 163 151 158 161 180 151 143
Weyerhaeuser-West 96 116 106 173 161 170 185 235 217 232
Northeastern Forest and Conservation Nursery
Association 205 242 225 215 198 178 212 193 170 126
Michigan Seedling Association 128 136 114 126 84 84 86 64 64 64
Michigan Herbaceous Perennials 650 637 613 563 319 316 267 0 0 0
Totals NA NA NA 3,199 2,845 2,816 2,885 2,653 2,388 2,448
Southern Forest Nursery Management Cooperative (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North
Carolina, Oklahoma, South Carolina, Tennessee, Texas and Virginia)
Northeastern Forest and Conservation Nursery Association (Illinois, Indiana, Kentucky, Maryland, Missouri, New Jersey, Ohio,
Pennsylvania, West Virginia and Wisconsin)
The Michigan Seedling Association includes one nursery in Indiana.
NA Not Available
Source: US Critical Use Exemption Nominations from the Phaseout of Methyl Bromide, 2006-2010: http://www.epa.gov/ozone/mbr/
Table 7. Effects of fumigation on numbers and sizes of plantable forest tree seedlings as
the average percent reduction in not treated compared to treated nursery beds compiled
from 36 published comparisons
% Reduction from the Controls (# of Comparisons)
Chemical Seedling Numbers Seedling Size N*W
MB 33 (99) 14 (36) 41
MBC33 33 (58) 1 (20) 28
Metam Sodium 27 (58) 5 (26) 5
Ethylene Dibromide 22 (17) -2 (12) 27
Dazomet 15 (48) 2 (28) 17
Formaldehyde 14 (5) 14 (4) 27
Chloropicrin 14 (13) 22 (12) 36
DD 6 (27) 6 (4) 3
Mean (Sum) 25 (345) 25 (142) 2
DD is a mixture of dichloropropane and dichloropropene
N*W is the difference in products of seedling weight and number for treatment minus that for
control as a percent of treatment
Source: [17]
Table 8. Treatment means for pine seedling production by soil treatment in Alabama 1994
Values per ft2 of nursery bed
Treatment Average root
collar diameter
Bed density-
spring
Bed density-
fall
Grade 1
seedlings
Control 4.0 c 22.8 ab 22.7 ab 2.2 c
Hot Water 4.1 bc 24.1 a 24.4 a 4.7 bc
MBC2 4.5 a 20.3 b 20.3 b 7.1 ab
Triform 4.5 a 24.0 a 22.6 ab 8.2 a
Sec/Chl 4.3 ab 24.1 a 22.9 ab 5.2 abc
MBC2: Methyl Bromide/Chloropicrin 98/2 at 350 lbs/acre
Triform: 1,3-dichloropropene at 235 lbs/acre plus chloropicrin at 115 lbs/acre
Sec/Chl: Metam sodium at 400 lbs/acre followed by chloropicrin at 126 lbs/acre
Source: [13]
Table 9. Nematodes (per 100 cc of soil) by soil treatment in Alabama 1994
Pathogens Saprophytes
Treatments June November June November
Control 0.5 52.3 108.3 a 164.2 a
Hot Water 1.8 46.0 85.7 ab 204.0 a
MBC2 0.7 0.0 41.3 b 141.0 a
Triform 0.0 3.7 41.7 253.0 a
Sec/Chl 0.0 16.0 68.0 ab 404.7 b
MBC2: Methyl Bromide/Chloropicrin 98/2 at 350 lbs/acre
Triform: 1,3-dichloropropene at 235 lbs/acre plus chloropicrin at 115 lbs/acre
Sec/Chl: Metam sodium at 400 lbs/acre followed by chloropicrin at 126 lbs/acre
Source: [13]
Table 10. Estimated Impacts of the Loss of Fumigants on Bareroot Forest Tree Seedling
Production in the Southern US by Seedling Type
Pine
Longleaf
Pine Hardwood Total
Seedling Production (1,000)1
687,859 6,504 30,472 724,835
Area (acres)2
2,179 38 309 2,526
Value of Production ($1000)3
$34,393 $585 $7,618 $42,596
Value of 33% Yield Loss
($1000) $11,350 $193 $2,514 $14,057
Cost Savings without
Fumigation4
$1,307 $23 $557 $1,887
Total Impact $10,043 $170 $1,957 $12,170
1 From [12].
2 Calculated assuming yields of 315,634/acre for pine, 171,573/acre for longleaf pine and
98,542/acre for hardwood [18].
3 Calculated assuming prices of $0.05/seedling for pine, $0.09/seedling for longleaf pine
and $0.25/seedling for hardwoods.
4 Calculated assuming $1800/acre cost of fumigation using methyl bromide and assuming
3 crops per fumigation cycle for pine and longleaf pine [16].
Table 11. Estimated Impacts of the Loss of Fumigants on Bareroot Forest Tree Seedling
Production in the Southeast by State
State Impact
($1000)
AL $1,079
AR $1,607
FL $661
GA $2,634
LA $492
MS $1,214
NC $668
OK $127
SC $1,798
TN $158
TX $1,304
VA $428
Total $12,170
Table 12. Estimated Impacts of the Loss of Fumigants on Forest Tree Seedling Production
by State Owned Nurseries in the Northeast by Stock Type
Stock Type
Conifer (1 yr.) Seedling Production (1,000)1
3,334,530
Area2
33
Value of Production ($1000)3
$866,978
Value of 33% Yield Loss ($1000) $286,103
Cost Savings without Fumigation4
$60,022
Total Impact $226,081
Conifer (2 yr.) Seedling Production (1,000)1
10,815,912
Area2
144
Value of Production ($1000)3
$2,812,137
Value of 33% Yield Loss ($1000) $928,005
Cost Savings without Fumigation4
$259,582
Total Impact $668,423
Conifer (3+ yrs.) Seedling Production (1,000)1
30,069,712
Area2
601
Value of Production ($1000)3
$10,524,399
Value of 33% Yield Loss ($1000) $3,473,052
Cost Savings without Fumigation4
$1,082,510
Total Impact $2,390,542
Deciduous Trees (1 yr.) Seedling Production (1,000)1
6,538,037
Area2
131
Value of Production ($1000)3
$2,092,172
Value of 33% Yield Loss ($1000) $690,417
Cost Savings without Fumigation4
$235,369
Total Impact $455,047
Deciduous Trees (2 yrs.) Seedling Production (1,000)1
4,576,395
Area2
92
Value of Production ($1000)3
$1,693,266
Value of 33% Yield Loss ($1000) $558,778
Cost Savings without Fumigation4
$164,750
Total Impact $394,028
Deciduous Trees (3+
yrs.)
Seedling Production (1,000)1
2,505,007
Area2
50
Value of Production ($1000)3
$726,452
Value of 33% Yield Loss ($1000) $239,729
Cost Savings without Fumigation4
$90,180
Total Impact $149,549
Deciduous Shrubs Seedling Production (1,000)1
3,097,103
Area2
62
Value of Production ($1000)3
$898,160
Value of 33% Yield Loss ($1000) $296,393
Cost Savings without Fumigation4
$111,496
Total Impact $184,897
1 From [14].
2 Calculated assuming yields of 100,000/acre for 1 yr. conifers, 75,000/acre for 2 yr.
conifers and 50,000/acre for 3 yr. conifers and all deciduous trees and shrubs [18].
3 Calculated assuming prices of $0.26/seedling for 1 and 2 yr. conifers, $0.35/seedling for
3 yr. conifers, $0.32/seedling for 1 year deciduous trees, $0.37/seedling for 2 and 2 year
deciduous trees and $0.29/seedling for deciduous shrubs.
4 Calculated assuming $1800/acre cost of fumigation using methyl bromide [16].
Table 13. Estimated Impacts of the Loss of Fumigants on Forest Tree Seedling Production
by State Owned Nurseries in the Northeast by State
State Impact
IL 123,278
IN 213,825
IA 84,644
KY 177,203
MD 166,429
MI 527,158
MN 764,882
MO 298,588
NH 22,091
NJ 32,245
NY 75,688
OH 0
PA 178,595
WI 1,724,008
WV 53,424
Total $4,468,568
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