1 

Report 04-13 June 2004

PREPLANT SOIL TREATMENT EFFECTS ON PRODUCTION OF 

 SEEDLINGS AT THE USDA FOREST SERVICE LUCKY PEAK NURSERY, 

BOISE, IDAHO 

R. L. James, G. R. Knudsen, and M. J. Morra 

ABSTRACT 

Tests were conducted at the USDA Forest Service Lucky Peak Nursery to compare four pre-sowing 

treatments on production of bare root ponderosa pine seedlings. Treatments tested included 

standard fumigation with methyl bromide–chloropicrin (MBC), fallowing with periodic cultivation, and 

two cultivars of Brassica napus incorporated into soil as green manure crops (“Dwarf Essex,” “Hybrid 

Mustard”). A biological control agent (Trichoderma harzianum) was also applied to some treatment 

areas. All treatments except MBC resulted in increased populations of Fusarium prior to sowing; the 

Brassica green manure crops greatly stimulated Fusarium populations. Seedling emergence, firstyear seedling survival and height were less in all nonfumigation treatments. Fusarium oxysporum

was the most frequently isolated pathogen from soil and diseased seedlings. Seedling height, 

diameter and root biomass on 2-0 seedlings were not significantly different among the treatments. 

Addition of T. harzianum had no effect on seedling production. Reduced seedling density, common 

in nonfumigation treatment areas, may result in larger seedlings. 

INTRODUCTION 

The USDA Forest Service Lucky Peak 

Nursery near Boise, Idaho has traditionally 

used preplant soil fumigation as a means of 

controlling soilborne pathogens, weeds, and 

improving bare root conifer seedling 

production. The fumigant of choice has been 

methyl bromide/chloropicrin (MBC), which is 

usually applied near the end or summer or 

early fall of the year prior to sowing when soil 

temperature and moisture conditions are most 

conducive for proper chemical soil 

penetration. Soil fumigation with MBC has 

resulted in sustained, predictable production 

of high-quality seedlings at the nursery for 

many years (Marshall 1983). 

Recently, methyl bromide has been targeted 

for phase out and elimination as a fumigant in 

the United States because of its propensity to 

degrade stratospheric ozone which affects 

penetration of ultraviolet light to the earth’s 

surface (Chapman 1992; Stone et al. 1995; 

World Meteorological Association 1995). The 

Montreal Protocol identified ozone-depleting 

chemicals and called for reduction and 

elimination of some of the more important 

ones (Evans and Greczy 1995; Shaheen 

1996). Use of methyl bromide is currently 
2 

being reduced and its use is scheduled for 

elimination by January 2005, even though 

some exemptions may be granted. Therefore, 

several investigations have been conducted at 

the Lucky Peak Nursery to identify and test 

viable alternatives to preplant soil fumigation 

with methyl bromide. Previous tests have 

involved alternative chemical fumigants 

(dazomet) (James and Beall 1999) and bare 

fallowing fields for at least one growing 

season prior to sowing (James and Beall 

2000). Neither of these treatments was 

deemed a viable alternative to methyl 

bromide. 

Brassica spp. incorporated into soil as a green 

manure crop may provide alternatives to preplant soil fumigation with chemical pesticides. 

Metabolites from certain cultivars have shown 

toxicity to common soilborne plant pathogens 

(Mayton et al. 1996) and may exhibit diseasesuppressive characteristics under agricultural 

conditions (Chung et al. 2002; Mayton et al. 

1996; Ramirez-Villapudua and Munnecke 

1988). Glucosinolates in Brassica tissues are 

converted to isothiocyanates upon 

decomposition (Mayton et al. 1996; Rosa and 

Rodrigues 1999); isothiocyanates, when 

produced in sufficient concentrations, may be 

toxic to certain soil pathogens. One way of 

supplementing possible disease suppressiveness of Brassica spp. is by incorporating 

biological control agents at the same time. 

Trichoderma harzianum has been successful 

in controlling soilborne pathogens in a number 

of agricultural settings (Knudsen and Bin 

1990; Knudsen et al. 1991). This fungus 

competes with and produces toxic metabolites 

that may inhibit important soilborne pathogens 

(Knudsen and Bin 1990; Papavizas 1985). 

An evaluation was conducted at the Lucky 

Peak Nursery to determine efficacy of 

selected Brassica cultivars as green manure 

crops, supplemented with application of T. 

harzianum, in controlling soilborne pathogens 

and production of high quality ponderosa pine 

seedlings. 

MATERIALS AND METHODS 

Tests were initiated during the summer of 

2000. Each treatment was replicated three 

times; treatment blocks were located within 

three sections of Field 14 in a complete 

randomized block design (figure 1). Each 

treatment block was 50 ft. (16.5 m) in length 

and two seedling beds wide. The treatments 

were: standard methyl bromide/chloropicrin 

(MBC) fumigation in August 2000 at the rate 

of 350 lbs/acre (= 390 kg/ha), bare fallowing 

with periodic cultivation, and two Brassica 

napus green manure crops (cultivars “Dwarf 

Essex” and “Hybrid Mustard”) that were sown 

in the late summer of 2000, grown over the 

winter, and incorporated into the soil 14 days 

before sowing in the spring of 2001. A 

formulation of Trichoderma harzianum (strain 

ThzID1) was added to half of the MBC, fallow, 

and Brassica plots just prior to sowing. 

Soil populations of potential pathogens in the 

genus Fusarium and potential antagonists in 

the genus Trichoderma were assayed prior to 

soil treatments and again just prior to sowing. 

Samples were collected from within each 

replicate plot; three collections within each 

plot were mixed together to represent a single 

sample. Each collection consisted of a soil 

core taken to a depth of about 8 inches (20 

cm). Soil was placed in plastic bags, kept 

refrigerated, and transported to the laboratory 

for analysis. 

Standard soil dilutions (Hildebrand and Dinkel 

1988, James et al. 1990, 1996, Stone et al. 

1995) were conducted to estimate populations 

of Fusarium and Trichoderma spp. Soil from 

each sample was initially sieved (2 mm sieve) 

to remove rocks, pieces of organic matter, and 

soil aggregates. From each sample, an 

approximate 5 g subsample was oven dried at 

about 100o

C for at least 24 hrs. until sample 

weight stabilized. Oven-dry weight was then 

calculated to provide a standard for sample 

comparison. For population assays, 0.05 g of 

field-moist soil was combined with 10 ml of 
3 

0.3% water agar (WA) and thoroughly mixed. 

One milliliter of solution was placed on each of 

three plates of selective agar medium for 

Fusarium and closely related fungi (Komada 

1975) and spread uniformly. Trichoderma

propagules were also enumerated on 

Komada’s medium which supports growth of 

this fungus unless amended with benomyl or 

lithium chloride. Plates were incubated for 7 

days at about 24o

C under diurnal cycles of 

cool, fluorescent light. Fusarium and 

Trichoderma colonies were identified by their 

morphology on the selective medium; 

populations were expressed as number of 

colony-forming units (cfu) per g of oven-dried 

soil. Selected Fusarium isolates were 

transferred to carnation leaf agar (Fisher et al. 

1982) and potato dextrose agar (PDA) for 

identification to species using the taxonomy of 

Nelson et al. (1983). Isolates of Trichoderma

were not identified to species. 

All plots were sown during early May 2001 

with the same seedlot of ponderosa pine 

(Pinus ponderosa Laws.) using standard 

nursery procedures and covered with fine 

sand. After seedling emergence was deemed 

complete (mid-July), three sampling subplots 

(1.5 ft2

 – 0.31 m2) were installed within each 

replicate plot; these subplots were located 

approximately equidistant from each other and 

concentrated within the center of each 

replicate plot (figure 2). Seedling emergence 

and postemergence damping off were 

determined within each subplot in July. At the 

same time, 10 diseased seedlings were 

randomly collected from each replicate plot for 

pathogen analysis in the laboratory. Selected 

seedlings were washed thoroughly, root/stem 

tissues surface sterilized in a 0.525% aqueous 

solution of sodium hypochlorite, and dissected 

into pieces about 5 mm in length. Twenty-five 

randomly selected pieces from seedlings 

Figure 1. Plot layout in Field 14 to evaluate effects of preplant soil treatments on production of 

bare root ponderosa pine seedlings - USDA Forest Service Lucky Peak Nursery, Boise, Idaho. 

Photo taken at the end of the first growing season. 
4 

within each replicate plot were placed on 

Komada’s medium and isolated organisms 

were identified as described above for soil 

samples. 

 At the end of the first growing season 

(October), seedling density and disease were 

determined within each subplot. Heights of 10 

seedlings within each subplot (if available) 

were measured at the same time. At the end 

of the first growing season, 100 diseased 1-0 

pine seedlings were randomly collected from 

throughout the study area. 

They were analyzed for pathogens by placing 

5 root or stem pieces from each seedling on 

Komada’s medium and identifying associated 

organisms as described above. Seedlings 

were washed and surface sterilized prior to 

isolations. 

At the end of the second growing season (fall 

2002), sample seedlings were carefully 

extracted from beds by hand for morphology 

measurements. Sample seedlings were 

located within inner seedling rows (to 

eliminate edge effects) and entire root 

systems were included with each seedling. 

Fifty “average” seedlings were collected from 

each replicate plot and transported to the 

laboratory for measurement. Seedling height 

(from basal cotyledon scar to the tip of the 

terminal bud), diameter (just above the ground 

line) and root mass (oven-dry weight of all 

attached roots) were determined for each 

sample seedling. Seedling heights, diameters, 

and root masses were compared among the 

treatments with an analysis of variance. 

Significant differences (P=0.05) in these three 

morphology categories were located using the 

least significant difference (LSD) procedure. 

RESULTS 

Presowing fumigation with MBC greatly 

reduced, but did not eliminate soil populations 

of Fusarium (table 1). Levels of Trichoderma

were also reduced, but not as drastically. The 

other nonfumigation treatments resulted in 

increased soil Fusarium populations, 

especially following incorporation of both 

Brassica green manure crops into soil. Soil 

Fusarium levels were well above estimated 

disease thresholds (> 1000 cfu/g) (Hildebrand 

and Dinkel 1988; James et al. 1990) in 

Brassica plots prior to sowing the conifer crop. 

Although Fusarium populations increased in 

the fallow treatments, presowing populations 

were slightly below disease threshold levels. 

Effects of the nonfumigation treatments on 

Figure 2. Borders of subplots (white pot labels) used for determining seedling emergence, firstyear survival, and level of disease within pre-plant treatment plots - USDA Forest Service Lucky 

Peak Nursery, Boise, Idaho. Seedlings with postemergence disease are indicated by arrows. 
5 

Trichoderma populations were variable (table 

1). 

Seedling responses to preplant soil treatments 

were evaluated by measuring seedling 

emergence, first-year survival, disease and 

height growth, and height, diameter and root 

mass production at the end of the second 

growing season. Treatment effects on 

seedling emergence and postemergence 

damping-off are summarized in table 2. 

Reduced seedling emergence and higher 

damping-off occurred in nonfumigated plots. 

Biocontrol treatment improved seedling 

emergence for all treatments except soil 

fumigation; effects on damping off were 

variable. Isolations from seedlings with 

postemergence damping-off symptoms (figure 

2) yielded high levels of Fusarium oxysporum

Schlecht. (table 3). Three different 

morphotypes of this species were routinely 

isolated from diseased seedlings. 

Morphotypes were differentiated on their 

cultural variability, i.e., production of aerial 

mycelium, violet pigmentation, and 

sporodochia (pionnotal). All three 

morphotypes produced spores characteristic 

of F. oxysporum: chlamydospores, 

macroconidia, and microconidia borne in false 

heads on short, unbranched monophialides 

(Nelson et al. 1983). Two other Fusarium

species (F. sporotrichioides Sherb. and F. 

solani (Mart.) Appel & Wollenw.) were isolated 

at very low levels (table 3). Trichoderma

isolates were isolated infrequently from 

diseased seedlings.

Table 1. Effects of pre-plant treatments on soil populations of Fusarium and Trichoderma

USDA Forest Service Lucky Peak Nursery, Boise, Idaho1

. 

Fusarium Trichoderma 

Treatment2 Replication 

Pre-Treat Pre-Sow Pre-Treat Pre-Sow 

1 168 0 4176 671

2 452 34 2563 371

3 486 0 3214 1212

Average 340.7 11.2 3317.6 751.2

A1 

% Change - 96.7 - 77.4 

1 349 1004 2775 1606

2 954 706 3031 1847

3 202 807 4297 1479

Average 489.8 838.8 3321.9 1644.3

A2 

% Change + 71.2 - 50.5 

1 1015 3424 1863 2920

2 469 19485 2853 1408

3 1366 4232 2735 6827

Average 945.1 9047.8 2527.9 3739.0

A3 

% Change + 857.3 + 47.9 

1 242 1108 3131 2417

2 442 9629 2141 3118

3 188 607 3178 1651

Average 290.5 3781.0 2816.7 2395.5

A4 

% Change + 1201.5 - 14.9 

1 Values in table are colony-forming units per gram of oven-dry soil. Percent change reflects changes from pre-treatment to 

pre-sowing populations. 2 A1 = fumigation with methyl bromide/chloropicrin; A2 = bare fallow with periodic cultivation; A3 = cultivation and incorporation 

of Dwarf Essex variety of Brassica; A4 = cultivation and incorporation of Hybrid Mustard variety of Brassica. 
6 

Table 2. Effects of pre-plant soil treatments on emergence of ponderosa pine seedlingsUSDA Forest Service Lucky Peak Nursery, Boise, Idaho1

. 

Treatment With Biocontrol Without Biocontrol 

Plot2 Emergence. Disease Emergence. Disease 

A-1-1 22.3 1.3 24.7 3.7 

A-1-2 22.7 1.3 25.3 3.7 

A-1-3 19.7 2.7 27.7 3.7 

Average 21.5 1.8 25.9 3.7 

A-2-1 21.3 5.7 14.3 3.3 

A-2-2 22.7 4.0 19.3 2.7 

A-2-3 11.7 4.3 19.0 2.0 

Average 18.5 4.7 17.5 2.7 

A-3-1 21.3 2.3 13.0 3.0 

A-3-2 18.7 2.0 11.0 2.7 

A-3-3 10.3 3.7 8.0 3.3 

Average 16.8 2.7 10.7 3.0 

A-4-1 18.0 3.3 12.3 2.0 

A-4-2 16.0 3.0 9.3 2.7 

A-4-3 15.3 3.7 4.3 5.0 

Average 16.4 3.3 8.7 3.2 

1 Values in table are number of seedlings per 0.31m2

. 2 A1 = fumigation with methyl bromide/chloropicrin; A2 = bare fallow with periodic cultivation; A3 = cultivation and incorporation 

of Dwarf Essex variety of Brassica; A4 = cultivation and incorporation of Hybrid Mustard variety of Brassica.

Table 3. Fusarium and Trichoderma isolated from diseased ponderosa pine seedlings at the 

end of seedling emergence - USDA Forest Service Lucky Peak Nursery, Boise, Idaho1

. 

Fusarium oxysporum3 Treatment2

Type 1 Type 2 Type 3 

Other 

Fusarium4 Trichoderma

A-1 88.0 32.0 9.3 0 9.3 

A-2 78.6 60.0 16.0 1.3 6.7 

A-3 88.0 70.7 24.0 0 14.7 

A-4 69.3 65.3 13.3 1.3 8.0 

All 81.0 57.0 15.6 0.7 9.7 

1 Values in table are percent of sampled root and stem pieces (75 sampled per treatment) colonized with the particular fungus.

2 A1 = fumigation with methyl bromide/chloropicrin; A2 = bare fallow with periodic cultivation; A3 = cultivation and incorporation 

of Dwarf Essex variety of Brassica; A4 = cultivation and incorporation of Hybrid mustard variety of Brassica.

3 Types based on cultural characteristics (aerial hyphae, pigmentation, sporodochial production).

4

 Includes F. sporotrichioides and F. solani.

Effects of preplant soil treatments on first-year 

seedling survival, height growth, and postemergence disease are summarized in table 

4. Seedling densities were less in all nonfumigation treatments, regardless of biocontrol 

agent application. Discernable seedling 

disease was low in all treatments. Seedlings 

were generally slightly taller within plots 

fumigated with MBC, although differences 

among treatments were small. 

Fusarium oxysporum was again the most 

commonly isolated pathogen from diseased 

1-0 seedlings (table 5). All three morphotypes 

of this species were well represented in 

isolations. Fusarium sporotrichioides was also 
7 

isolated; Trichoderma spp. were isolated at 

low levels. 

Preplant soil treatment effects on height, 

diameter, and root mass production of 2-0 

seedlings are summarized in table 6. No 

significant differences were found in any of the 

measured morphology parameters among the 

four treatments. In addition, amendments with 

the biocontrol agent did not significantly affect 

seedling production. Similar-sized seedlings 

were produced from all treatments by the end 

of the second growing season. 

DISCUSSION 

Root diseases caused primarily by Fusarium 

oxysporum are important in limiting production 

of bare root pine seedlings at the Lucky Peak 

Nursery (James 2002; James and Beall 1999, 

2000). Disease levels tend to vary among the 

different production fields and are also 

influenced by environmental factors, 

particularly moisture and ambient 

temperatures. Most root disease occurs 

during the first growing season (James 2001, 

2002); seedlings surviving the first year 

usually grow well the second season and 

reach desired sizes. However, seedling 

densities may be reduced by first-year root 

diseases and the required number of quality 

seedlings may not be obtained. 

Preplant soil fumigation with MBC has been 

effective at the nursery for many years 

(Marshall 1983). Although expensive, 

fumigation has generally resulted in denser 

seedbeds and larger, healthier seedlings. 

Because of the impending loss of methyl 

bromide as a fumigant, several trials have 

been conducted at the nursery to identify 

viable alternatives. The fumigant dazomet 

(Basamid®) was not as effective at Lucky 

Peak as other nurseries (James and Beall 

(1999), primarily because heavy soils with 

Table 4. Effects of pre-plant soil treatments on first-year seedling survival, disease, and 

height growth - USDA Forest Service Lucky Peak Nursery, Boise, Idaho. 

Treatment With Biocontrol Without Biocontrol 

Plot1 Live2 Dead2 Height3 Live2 Dead2 Height3

A-1-1 20.7 1.3 6.02 23.0 1.3 7.25 

A-1-2 22.0 1.3 7.65 21.3 1.3 8.25 

A-1-3 24.3 0.7 8.17 19.7 1.7 9.70 

Average 22.3 1.1 7.28 21.3 1.4 8.40 

A-2-1 20.7 0.7 7.05 13.0 0.7 8.39 

A-2-2 17.7 2.0 7.22 20.0 0.7 8.67 

A-2-3 10.0 2.0 7.30 16.3 1.0 7.78 

Average 16.1 1.5 7.19 16.4 0.8 8.28 

A-3-1 18.7 1.3 6.70 13.3 0.7 7.55 

A-3-2 10.7 0.3 7.02 16.3 2.0 7.12 

A-3-3 6.7 1.0 7.27 8.3 1.7 6.76 

Average 12.0 0.9 6.96 12.7 1.4 7.16 

A-4-1 15.3 0.3 6.81 13.0 0.3 7.40 

A-4-2 14.0 2.3 7.68 8.0 0.7 7.85 

A-4-3 10.3 0.7 7.89 6.3 1.3 9.32 

Average 13.2 1.1 7.44 9.1 0.8 8.05 

All 15.9 1.2 7.22 14.9 1.1 7.98 

1 A1 = fumigation with methyl bromide/chloropicrin; A2 = bare fallow with periodic cultivation; A3 = cultivation and incorporation of Dwarf 

Essex variety of Brassica; A4 = cultivation and incorporation of Hybrid Mustard variety of Brassica

2 Number of seedlings per 0.31m2

. 3 Average height of 10 seedlings - if available (cm).
8 

Table 5. Fusarium and Trichoderma isolated from diseased ponderosa pine seedlings at the 

end of the first growing season - USDA Forest Service Lucky Peak Nursery, Boise, Idaho.1

Fungus Infection1 Colonization2

Fusarium oxysporum3

Type 1 

82 68.2 

Type 2 82 60.4 

Type 3 62 26.0 

All Isolates 100 100 

Fusarium sporotrichioides 2 0.8 

Trichoderma 20 5.0 

1 Percent of 100 seedlings sampled infected with the particular fungus. 2 Percent of stem and root pieces sampled (5 per seedling) colonized with the particular fungus. 

3 Types based on cultural characteristics (aerial hyphae, pigmentation, sporodochial production).

Table 6. Effects of pre-plant soil treatment on 2-0 seedling density, height, diameter, and 

root biomass - USDA Forest Service Lucky Peak Nursery, Boise, Idaho. 

Treatment1

Average Height 

(cm) 

Average Diameter 

(mm) 

Average Root Mass 

(g) 

A1 + Biocontrol 25.8 6.2 2.54 

A1 – Biocontrol 22.7 5.4 1.94 

A2 + Biocontrol 23.1 6.1 2.78 

A2 – Biocontrol 21.7 5.9 3.07 

A3 + Biocontrol 21.7 6.4 3.21 

A3 – Biocontrol 22.2 6.2 2.94 

A4 + Biocontrol 22.1 6.6 3.50 

A4 – Biocontrol 22.5 6.1 2.99 

All “A1” 24.3 A2 5.8 A2 2.24 A2

All “A2” 22.4 A 6.0 A 2.93 A 

All “A3” 22.0 A 6.3 A 3.08 A 

All “A4” 22.3 A 6.4 A 3.25 A 

All + Biocontrol 23.2 A3 6.3 A3 3.01 A3

All – Biocontrol 22.3 A 5.9 A 2.74 A 

1

A1 = fumigation with methyl bromide/chloropicrin; A2 = bare fallow with periodic cultivation; A3 = cultivation and incorporation 

of Dwarf Essex variety of Brassica; A4 = cultivation and incorporation of Hybrid Mustard variety of Brassica. Biocontrol treatments 

were addition of Trichoderma harzianum strain ThzlD1. 2 For comparisons among the four treatments, means followed by the same letter are not statistically different (P=0.05) using the least 

significant difference (LSD) procedure.

3 For comparisons between treatments with and without biocontrol amendments, means followed by the same letter are not statistically 

different (P=0.05) using the least significant difference (LSD) procedure.

high clay content restricted distribution of the 

fumigant throughout the soil profile (Munnecke 

and Van Gundy 1979). Likewise, fallowing 

fields with periodic cultivation was not very 

effective in reducing soil pathogen inoculum or 

improving seedling production, particularly in 

fields with heavier soils and poorer water 

drainage (James and Beall 2000). 

Our results indicated that incorporating 

Brassica green manure crops into soil initially 

caused extensive increases in soil Fusarium

populations, including F. oxysporum. This 
9 

population increase adversely affected 

seedling emergence and growth during the 

first growing season. Higher levels of preemergence disease probably resulted from 

increased Fusarium levels; postemergence 

disease may not have been as severe. 

However, during the second growing season, 

seedlings were much less affected. Seedlings 

surviving to the end of the second growing 

season grew well and were generally healthy 

regardless of the preplant treatment. By the 

time of lifting, seedlings produced in all areas 

were similar. Therefore, the most important 

benefit of soil fumigation was first-year 

seedling establishment and performance. 

Reductions in seedling density may occur 

because of higher first-year root disease. 

However, root diseases did not greatly affect 

seedlings during the second growing season. 

If sufficient area is available for bare root 

seedling production at the nursery, reduced 

seedling densities may not be of concern. 

However, high first-year disease means that 

sowing densities must remain high to achieve 

desired number of seedlings. 

Biological control with one strain of 

Trichoderma harzianum has thus far not 

effectively controlled soilborne diseases in 

tested forest nurseries (James 2000; James et 

al. 2004). We found little effect of this 

biocontrol agent in our tests, other than limited 

improvement in seedling emergence in plots 

treated with Brassica green manure crops. 

There may have been some amelioration of 

resident Fusarium populations by the 

biocontrol agent, but this was difficult to 

measure. 

Tests of Brassica green manure crops to 

reduce soilborne diseases in forest nurseries 

have so far been disappointing. Although such 

treatments were effective in some agricultural 

systems (Angus et al. 1994; Chung et al. 

2002), similar results have not been 

forthcoming in forest nurseries (Hansen et al. 

1990; Hamm and Hansen 1990; James et al. 

2004). It is likely that the level of 

glucosinolates produced by tested Brassica

cultivars following soil incorporation is 

insufficient to offset the proliferation of 

pathogen populations that occur because of 

adding large amounts of organic matter 

(Hansen et al. 1990). This could be caused by 

inefficient release of isothiocyanates from the 

tissues, a key step that requires extensive 

tissue maceration and ample water (Morra 

and Kirkegaard 2002). Alternatively, 

glucosinolates present within B. napus tissues 

may not produce products that are biologically 

active against F. oxysporum. The latter 

possibility is plausible, given the fact that B. 

napus does not container glucosinolates that 

release 2-propenyl isothiocyanate (Gardiner et 

al. 1999), an isolthiocyanate that was shown 

to inhibit mycelial growth and completely 

suppress conidial and chlamydospore 

germination (Smolinska et al. 2003). 

Fusarium spp. are excellent saprophytes on a 

wide range of organic matter. Their 

populations respond directly to soil additions 

of organic matter and may stabilize when food 

sources become scarcer. Fusarium 

oxysporum responds to added organic matter 

like other Fusarium spp. This fungal species 

makes up the vast majority of the Fusarium

population at the Lucky Peak Nursery (James 

and Beall 1999, 2000) and is almost 

exclusively the species isolated from diseased 

as well as healthy seedling root systems 

(James 2000, 2001, 2002). Not all isolates of 

F. oxysporum are pathogens (Gordon and 

Martyn 1997; Gordon and Okamoto 1992). 

However, pathogenic and nonpathogenic 

isolates appear morphologically similar and 

cannot easily be differentiated. Controlled 

pathogenicity tests have been successful in 

locating pathogenic strains (James et al. 

2000), but more promising techniques include 

molecular genetic analyses (Assighetse et al. 

1994; Gordon and Martyn 1997; Kim et al. 

1993; Kistler 1997). If molecular probes can 

be developed to locate pathogenic strains of 

F. oxysporum from forest nurseries, growers 

will be in a much better position to predict 

disease severity from information about 

resident populations of this fungus. 

The Lucky Peak Nursery has a long history of 

producing high-quality bare root forest 

seedlings, particularly pine species. This has 

been possible by routine preplant soil 

fumigation with MBC. The future without 
10 

methyl bromide may result in greater 

problems with bare root seedling production, 

primarily because of expected higher levels of 

root disease. This may partly be overcome by 

conversion of production to containers, which 

is being actively pursued at the nursery. For 

example, a new greenhouse facility was 

recently installed which will be able to produce 

thousands of container seedlings annually. 

This will likely reduce the need for but will not 

eliminate bare root production in the future. 

Therefore, continued efforts to identify viable 

alternatives to methyl bromide fumigation at 

the Lucky Peak Nursery will be necessary. 

LITERATURE CITED 

Angus, J.F., P.A. Gardner, J.A. Kirkegaard 

and J.M. Desmarchelier. 1994. 

Biofumigation: isothiocyanates released 

from Brassica roots inhibit growth of the 

take-all fungus. Plant and Soil 162:107-112. 

Assigbetse, K.B., D. Fernandez, M.P. Dubois 

and J.-P. Geiger. 1994. Differentiation of 

Fusarium oxysporum f.sp. vasinfectum

races on cotton by random amplified 

polymorphic DNA (RAPDs) analyis. 

Phytopathology 84:622-626. 

Chapman, W. 1992. Alternative treatments to 

methyl bromide. In: Conference 

Proceedings: Southern Forest Nursery 

Association 1992:96-103. 

Chung, W.C., J.W. Huang, H.C. Huang and 

J.F. Jen. 2002. Effect of ground Brassica

seed meal on control of Rhizoctonia

damping-off of cabbage. Canadian Journal 

of Plant Pathology 24:211-218. 

Evans, G.R. and L.M. Greczy. 1995. Methyl 

bromide: the cure-all of the horticulture 

industry will be banned by 2001. When this 

happens, what, if anything, will take its 

place. American Nurseryman 182(7):95-105. 

Fisher, N.L., L.W. Burgess, T.A. Toussoun 

and P.E. Nelson. 1982. Carnation leaves as 

a substrate and for preserving cultures of 

Fusarium species. Phytopathology 72:151-

153. 

Gardiner, J.B., M.J. Morra, C.V. Eberlein, P.D. 

Brown and V. Borek. 1999. Allelochemicals 

released in soil following incorporation of 

rapeseed (Brassica napus) green manures. 

Journal of Agricultural and Food Chemistry 

47:3837-3842. 

Gordon, T.R. and R.D. Martyn. 1997. The 

evolutionary biology of Fusarium 

oxysporum. Annual Review of 

Phytopathology 35:111-128. 

Gordon, T.R. and D. Okamoto. 1992. 

Population structure and the relationship 

between pathogenic and non-pathogenic 

strains of Fusarium oxysporum. 

Phytopathology 82:73-77. 

Hansen, E.M., D.D. Myrold and P.B. Hamm. 

1990. Effects of soil fumigation and cover 

crops on potential pathogens, microbial 

activity, nitrogen availability, and seedling 

quality in conifer nurseries. Phytopathology 

80:698-704. 

Hamm, P.B. and E.M. Hansen. 1990. Soil 

fumigation, cover cropping, and organic soil 

amendments: their effect on soil-borne 

pathogens and the target seedlings. In: 

Rose, R., S.J. Campbell and T.D. Landis 

(eds.). Target Seedling Symposium: 

Proceedings, Combined Meeting of the 

Western Forest Nursery Associations. 

USDA Forest Service, Rocky Mountain 

Experiment Station. General Technical 

Report RM-200. pp. 174-180. 

Hildebrand, D.M. and G.B. Dinkel. 1988. 

Evaluation of methyl bromide, Basamid 

granular, and solar heating for pre-plant pest 

control for fall-sown eastern redcedar at 

Bessey Nursery. USDA Forest Service, 

Rocky Mountain Region, Timber, Forest 

Pest, and Cooperative Forestry 

Management. Technical Report R2-41. 13p. 

James, R.L. 2000. Effects of topical 

application of the biological control agent 

Biotrek on production of bareroot Douglasfir and western white pine seedlings – USDA 

Forest Service Nursery, Coeur d’Alene, 

Idaho. USDA Forest Service, Northern 
11 

Region, Forest Health Protection. Report 00-

5. 8p. 

James, R.L. 2001. Effects of pre-sowing soil 

treatments on root colonization of 1-0 

ponderosa and lodgepole pine seedlings by 

potentially-pathogenic fungi - USDA Forest 

Service Lucky Peak Nursery, Boise, Idaho. 

USDA Forest Service, Northern Region, 

Forest Health Protection. Report 01-9. 9p. 

James, R.L. 2002. Effects of preplant soil 

treatments on Fusarium and Trichoderma

populations and fungal root colonization of 

1-0 nondiseased ponderosa pine seedlings - 

USDA Forest Service Lucky Peak Nursery – 

Boise, Idaho. USDA Forest Service, 

Northern Region, Forest Health Protection. 

Report 02-3. 9p. 

James, R.L. and K. Beall. 1999. An evaluation 

of the effects of dazomet on soil-borne 

diseases and conifer seedling productionUSDA Forest Service Lucky Peak Nursery, 

Boise, Idaho. USDA Forest Service, 

Northern Region, Forest Health Protection. 

Report 99-9. 15p. 

James, R.L. and K. Beall. 2000. Effects of 

fallowing on Fusarium-associated root 

diseases and production of bare root 

ponderosa pine seedlings at the USDA 

Forest Service Lucky Peak Nursery, Boise, 

Idaho. USDA Forest Service, Northern 

Region, Forest Health Protection. Report 

00-3. 13p. 

James, R.L., G.R. Knudsen and M.J. Morra. 

2004. Effects of pre-plant soil treatments on 

production of Douglas-fir seedlings - USDA 

Forest Service Nursery, Coeur d’Alene, 

Idaho. USDA Forest Service, Northern 

Region, Forest Health Protection. Report 04-

10. 14p. 

James, R.L., S. Metzger and C.J. Gilligan. 

1990. Effects of soil fumigation on conifer 

seedling production at the USDA Forest 

Service Nursery, Coeur d’Alene, Idaho. 

USDA Forest Service, Northern Region, 

Forest Pest Management. Report 90-11. 

18p. 

James, R.L., D.S. Page-Dumroese, S.K. 

Kimball and S. Omi. 1996. Effects of 

Brassica cover crop, organic amendment, 

fallowing, and soil fumigation on production 

of bareroot Douglas-fir seedlings - USDA 

Forest Service Nursery, Coeur d’Alene, 

Idaho. USDA Forest Service, Northern 

Region, Forest Health Protection. Report 96-

6. 10p. 

James, R.L., R. Perez, R.K. Dumroese and 

D.L. Wenny. 2000. Virulence of Fusarium 

oxysporum on Douglas-fir germinants: 

comparison of isolates from nursery soil and 

roots of healthy and diseased seedlings. In: 

Lilja, A. and J.R. Sutherland (eds.). 

Proceedings of the 4th Meeting of IUFRO 

Working Party 7.03.04 – Diseases and 

Insects in Forest Nurseries. Finnish Forest 

Research Institute, Research Papers 781. 

pp. 49-64. 

Kim, D.H., R.D. Martyn and C.W. Magill. 1993. 

Mitochondrial DNA (mtDNA) relatedness 

among formae speciales of Fusarium 

oxysporum in the Cucurbitae. 

Phytopathology 83:91-97. 

Kistler, H.C. 1997. Genetic diversity in the 

plant-pathogenic fungus Fusarium 

oxysporum. Phytopathology 87:474-479. 

Komada, H. 1975. Development of a selective 

medium for quantitative isolation of 

Fusarium oxysporum from natural soil. 

Review of Plant Protection Research 

(Japan) 8:114-125. 

Knudsen, G.R. and L. Bin. 1990. Effects of 

temperature, soil moisture, and wheat bran 

on growth of Trichoderma harzianum from 

alginate pellets. Phytopathology 80:724-727. 

Knudsen, G.R., D.J. Eschew, L.M. Dandurand 

and Z.G. Wang. 1991. Method to enhance 

growth and sporulation of pelletized 

biocontrol fungi. Applied and Environmental 

Microbiology 57:2864-2867. 

Marshall, J.P. 1983. Effectiveness of methyl 

bromide/chloropicrin fumigation in reducing 

Fusarium populations in two major soil types 
12 

at the USDA Forest Service Lucky Peak 

Nursery. USDA Forest Service, 

Intermountain Region, Forest Pest 

Management. Report 83-6. 9p. 

Mayton, H.S., C. Oliviker, S.F. Vaughn and R. 

Loria. 1996. Correlation of fungicidal activity 

of Brassica species with allyl isothiocyanate 

production in macerated leaf tissue. 

Phytopathology 86:267-271. 

Morra, M.J. and J.A. Kirkegaard. 2002. 

Isothiocyanate release from soilincorporated Brassica tissues. Soil Biology & 

Biochemistry 34:1683-1690. 

Munnecke, D.E. and S.D. Van Gundy 1979. 

Movement of fumigants in soil, dosage 

responses, and differential effects. Annual 

Review of Phytopathology 17:405-429. 

Nelson, P.E. T.A. Toussoun and W.F.O. 

Marasas. 1983. Fusarium species: an 

illustrated manual for identification. The 

Pennsylvania State University Press, 

University Park. 193p. 

Papavizas, G.C. 1985. Trichoderma and 

Gliocladium: biology, ecology, and potential 

for biocontrol. Annual Review of 

Phytopathology 23:23-54. 

Ramirez-Villapudua, J. and D.E. Munnecke. 

1988. Effect of solar heating and soil 

amendments of cruciferous residues on 

Fusarium oxysporum f.sp. conglutinans and 

other organisms. Phytopathology 78:289-

295. 

Rosa, E.A.S. and P.M.F. Rodrigues. 1999. 

Towards a more sustainable agriculture 

system: The effect of glucosinolates on the 

control of soil-borne diseases. Journal of 

Horticultural Science & Biotechnology 

74:667-674. 

Shaheen, L. 1996. Potential loss of methyl 

bromide to prompt changes in Clean Air Act. 

Pest Control 64(5):68,74 

Smolinska, U., M.J. Morra, G.R. Knudsen and 

R. L. James. 2003. Isothiocyanates 

produced by Brassicaceae species as 

inhibitors of Fusarium oxysporum. Plant 

Disease 87:407-412. 

Stone, J.K., D.M. Hildebrand, R.L. James, 

S.M. Frankel and D.S. Germandt. 1995. 

Alternatives to methyl bromide for control of 

soil-borne diseases in bare root forest 

nurseries. In: Proceedings: Annual 

International Research Conference on 

Methyl Bromide Alternatives and Emissions 

Reductions. November 6-8, 1995, San 

Diego, CA. Methyl Bromide Alternatives 

Outreach, US Environmental Protection 

Agency and US Department of Agriculture. 

pp. 77-1 – 77-4. 

World Meterological Association. 1995. 

Scientific assessment of ozone depletion: 

1994 executive summary. Global Ozone 

Research and Monitoring Project Report No. 

37. Global Ozone Observing System, 

Geneva, Switzerland. 36p.

R.L. James is Plant Pathologist, USDA Forest Service, Northern Region, Forest Health Protection. 

Address: USDA Forest Service, 3815 Schreiber Way, Coeur d’Alene, ID 83814; email 

rjames@fs.fed.us. G.R. Knudsen and M.J. Morra are with the Soil & Land Resources Division, 

University of Idaho, Moscow 83844-2339; email: (G.R. Knudsen): microbes@moscow.com; 

(M.J. Morra): mmorra@uidaho.edu.