The Importance of Soil Fumigation: Forest Seedlings -

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.

http://www.epa.gov/ozone/mbr/cun2009/cun2009_Seedling.pdf

http://www.nationalplantboard.org/laws/index.html

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

http://www.epa.gov/ozone/mbr/2012_nomination.html

https://nurserycoop.auburn.edu/images/chloropic.jpg

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/

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


$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


$2,812,137



$259,582


Conifer (3+ yrs.) Seedling Production (1,000)1

30,069,712

Area2

601


$10,524,399

Value of 33% Yield Loss ($1000) $3,473,052


$1,082,510

Total Impact $2,390,542

Deciduous Trees (1 yr.) Seedling Production (1,000)1

6,538,037

Area2

131


$2,092,172



$235,369


Deciduous Trees (2 yrs.) Seedling Production (1,000)1

4,576,395

Area2

92


$1,693,266



$164,750


Deciduous Trees (3+

yrs.)

Seedling Production (1,000)1

2,505,007

Area2

50


$726,452



$90,180


Deciduous Shrubs Seedling Production (1,000)1

3,097,103

Area2

62


$898,160



$111,496


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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The Importance of Soil Fumigation: Forest Seedlings -