United States 

Department of 

Agriculture 

Forest 

Service 

Northern 

Region 

200 East Broadway 

P.O. Box 7669 

Missoula, MT 59807 

Report 04-10 May 2004

PREPLANT SOIL TREATMENT EFFECTS ON PRODUCTION OF 

DOUGLAS-FIR SEEDLINGS AT THE USDA FOREST SERVICE NURSERY, 

COEUR D’ALENE, IDAHO 

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

ABSTRACT 

Six pre-plant soil treatments were evaluated for their effects on soil populations of potentially-pathogenic 

Fusarium and Pythium spp. and saprophytic Trichoderma spp. and production of bare root Douglas-fir 

seedlings at the USDA Forest Service Nursery, Coeur d’Alene, Idaho. Incorporating green manure crops 

of Brassica juncea and composted sewage sludge resulted in large increases of Fusarium spp. Resulting 

seedling production was not improved over either dazomet fumigation or fallowing by incorporating 

Brassica green manure crops. Steam treatment of soil reduced potential pathogen populations, but did 

not result in improved seedling production when compared to fallowing and dazomet fumigation. Addition 

of the biocontrol agent Trichoderma harzianum following incorporation of Brassica green manure crops 

did not affect either pathogen populations or seedling production. Plastic tarps to reduce volatile losses 

of decomposition products of Brassica residues only reduced soil Pythium levels and did not improve 

seedling production. Results of this evaluation indicated that the Brassica cultivar tested did not provide 

effective disease control and could not be used as a viable alternative to either dazomet fumigation or 

fallowing for producing high-quality conifer seedlings at the Coeur d’Alene Nursery. 

INTRODUCTION 

Bare root forest seedling production in the 

United States has routinely depended on preplant soil fumigation with chemical biocides to 

ensure production of high-quality stock for 

reforestation. Most nurseries have relied on 

methyl bromide/chloropicrin (MBC) mixtures for 

fumigation (Boone 1988; Boyd 1971; Ibarbia 

1995; James 1989). However, methyl bromide is 

currently being phased out and scheduled for 

elimination as a soil fumigant in January 2005, 

primarily because it significantly contributes to 

the deterioration of ultraviolet light-protective 

stratospheric ozone (Shaheen 1996; World 

Meterological Association 1995). Methyl bromide 

has been a very effective soil fumigant for many 

years and, as a result, many nurseries have 

become reliant on this chemical. However, 

evaluations of possible alternatives to methyl 

bromide and/or pre-plant soil fumigation have 

been conducted at some nurseries (Chapman 

1992; James et al. 1996; Linderman et al. 1994) 
2 

The USDA Forest Service Nursery in Coeur 

d’Alene, Idaho has a history of using pre-plant 

soil fumigants to control soilborne plant 

pathogens and weeds. MBC had been the 

fumigant of choice, but was recently replaced 

with dazomet (Basamid granular®) because it 

was as effective as MBC and had less potential 

adverse environmental consequences (James et 

al. 1990, 1996). Dazomet is usually applied in 

the late summer or early fall prior to sowing the 

following spring. It is applied topically, cultivated 

into the soil and activated/sealed with overhead 

irrigation. The chemical becomes volatile when 

wetted and does not require tarping with plastic 

polyethylene like MBC (James and Beall 1999; 

James et al. 1996; Miller and Norris 1970). 

Although dazomet is effective at the Coeur 

d’Alene Nursery (James et al. 1990, 1996), it is 

expensive, requires expert applicators, and still 

presents potential environmental risks at the 

nursery. Therefore, growers have encouraged 

development of possible alternatives to all 

chemical soil fumigation. A series of tests have 

been conducted at the nursery to evaluate costeffective, efficacious alternatives to chemical soil 

fumigation. This report summarizes findings of 

tests involving six different soil treatments on the 

production of Douglas-fir (Pseudotsuga 

menziesii Franco var. glauca [Mayr.] Sudw.) 

seedlings at the nursery. 

MATERIALS AND METHODS 

Tests were initiated during the summer of 1996. 

Each treatment was replicated five times; 

treatment blocks were located within a section of 

Field 9 in a complete randomized block design. 

Each treatment block was 50 ft (15.5 m). in 

length and one seedling bed width, with the 

exception of the dazomet treatments which were 

two bed widths because of the application 

machinery requirements. The six treatments 

were: (1) standard dazomet soil fumigation (300 

lbs./acre; 335 kg/hectare); (2) bare fallowing with 

periodic cultivation; (3) mustard (Brassica juncea 

– variety Pacific Gold) green manure crop that 

was incorporated into the soil (figure 1) after 6 

weeks’ growth and covered with a 2 mil clear 

polyethylene tarp; (4) mustard green manure 

crop without tarp; (5) topical applications of 

composted sewage sludge to a depth of 2.5 cm 

(figure 3)and then tilled into soil; (6) steam 

treatment of soil with a machine fabricated by 

the USDA Forest Service Technology 

Development Center (Missoula, Montana)(figure 

4). Soil temperatures from steam treatments 

varied with depth and time after treatment. 

Maximum temperatures reached about 68o

C at 

13 cm just after treatment. Temperatures 

exceeding 63o

C were detected below 20 cm 

from the soil surface. To evaluate potential 

effects of a biological control agent on these 

treatments, a formulation of Trichoderma 

harzianum Rifai (strain ThzID1) was added to a 

portion of the dazomet, fallow, and mustard (no 

tarp) treatments just prior to sowing in the spring 

of 1997. 

Soil populations of potential pathogens in the 

genera Fusarium and Pythium and potential 

antagonists in the genus Trichoderma were 

assayed three times during the test. The first 

sample was taken in July, 1996 (pre-treatment); 

the second in October, 1996 (post-treatment) 

and the third in late April, 1997 (pre-sowing). 

Samples were collected from within each 

replicate plot; three cores from near the center 

of each plot were collected and 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 
3 

Figure 1. Brassica juncea green manure crop flowering after being 

grown for 6 weeks at the USDA Forest Service Nursery, 

Coeur d’Alene, Idaho 

Figure 2. Incorporation of Brassica juncea green 

manure crop into soil after chopping - USDA Forest 

Service Nursery, Coeur d’Alene, Idaho 
4 

Figure 3. Topical application 

of sewage sludge compost on 

a replicate-plot - USDA Forest 

Service Nursery, 

Coeur d’Alene, Idaho. 

Compost was incorporated 

into soil after application. 

Figure 4. Injecting steam into 

soil to control soilborne 

pathogens - USDA Forest 

Service Nursery, 

Coeur d’Alene, Idaho. 
5 

Standard soil dilutions (Hildebrand and Dinkel 

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

1995) were conducted to estimate populations of 

Fusarium, Trichoderma, and Pythium 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 h until sample weight 

stabilized. Oven-dry weight was then calculated 

to provide a standard for sample comparison. 

For assays of Fusarium and Trichoderma 

populations, 0.05 g of field-moist soil was 

combined with 10 ml of 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 readily supports 

growth of this fungus unless the medium is 

amended with benomyl or lithium chloride. 

Plates were incubated at least 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 gram of ovendried soil (it was assumed that each fungal 

colony originated from one propagule). Selected 

Fusarium isolates were transferred to carnation 

leaf agar (Fisher et al. 1982) and potato 

dextrose agar (PDA) for species identification 

using the taxonomy of Nelson et al. (1983). 

Ratios of Trichoderma to Fusarium populations 

were calculated for each treatment; these ratios 

may indicate a very rough estimate of potential 

disease suppressiveness of the soil since 

Trichoderma spp. are known antagonists of a 

wide range of soilborne plant pathogens, 

including Fusarium spp. (Papavizas 1985). 

For assays of Pythium populations, 0.5 g of soil 

was combined with 10 ml of 0.3% WA. One 

milliliter of solution was placed on each of three 

plates containing another selective medium 

consisting of V-8 juice agar amended with the 

antibiotics pimaricin, rifamycin, and ampicillin 

and the fungicide pentachloronitrobenzene 

(James et al. 1990, 1996; Stone et al. 1995). 

Plates were incubated in the dark at about 24o

C 

for 3 days. Pythium colonies were identified on 

the basis of their diameter after 3 days (15-20 

mm), feathery margin, and growth within rather 

than superficially on the agar surface. 

Populations were expressed as cfu/g of ovendried soil. Selected Pythium isolates were 

transferred to PDA for identification using the 

taxonomy of Waterhouse (1968) 

Brassica juncea tissues were obtained 

immediately prior to incorporating the crop into 

soil by randomly selecting four plants from the 

center of each replicate plot. The plants were 

stored on ice for transport to the laboratory 

where they were frozen, freeze-dried, and 

ground to a fine powder. Glucosinolate analysis 

of plant tissues was performed using GC-MS 

(Gardiner et al. 1999). 

All plots were sown during early May, 1997 with 

the same seedlot of Douglas-fir using standard 

nursery procedures and covered with 

hydromulch. After complete seedling emergence 

(mid-July), three sampling sub-plots (0.5 m2

) 

were installed within each replicate-plot; these 

subplots were located approximately equidistant 

from each other within the center of each 

replicate-plot. Seedling emergence and postemergence damping-off were determined in 

each sub-plot in July; selected damped-off 

seedlings were collected for laboratory analysis 

of associated pathogens. At the end of the first 

growing season (October 1997), seedling 

density and disease were determined within 

each sub-plot. Selected diseased seedlings 

were again collected for laboratory analysis, 

which included thoroughly washing roots and 

incubating them on Komada’s medium and 

identifying associated organisms as described 

above. 

At the end of the second growing season 

(November 1998), seedling density within each 

replicate-plot was determined using standard 

nursery density measurements (number of 

seedlings per 0.32 m with bed widths of 1.12 m 

and 7 rows of seedlings). After density 

estimates, sample seedlings were carefully 

extracted from beds for morphology 

measurements. Sample seedlings were located 

within inner seedling rows to eliminate edge 

effects. Fifty “average” seedlings were collected 

from each replicate plot. Seedlings were 
6 

transported to the laboratory for measurement. 

Seedling height (from basal cotyledon scar to 

the tip of the terminal bud), diameter (just above 

the groundline) and root mass (oven-dry weight 

of all roots) were determined for each sample 

seedling. Seedling heights, diameters, and root 

masses were compared among the six 

treatments with an analysis of variance. 

Significant differences (P=0.05) in these three 

morphology categories were located using the 

LSD procedure. 

RESULTS 

The only soil treatments that resulted in reduced 

populations of Fusarium by the time of sowing 

were dazomet fumigation and steam 

applications (table 1). Adding organic matter in 

the form of incorporated Brassica crops and 

composted sewage sludge resulted in extensive 

increases in Fusarium populations; such 

increases were extremely large in the Brassica

green manure plots by the time of sowing. The 

vast majority of the Fusarium population in all 

plots was comprised of isolates of F. oxysporum

Schlecht. (table 2). Six other Fusarium species 

[F. solani (Mart.) Appel & Wollenw., F. equiseti

(Corda) Sacc., F. avenaceum (Fr.) Sacc., F. 

acuminatum Ell. & Ev., F. sambucinum Fuckel 

and F. culmorum (W.G. Smith) Sacc.] were 

isolated infrequently (table 2). 

Soil populations of Trichoderma spp. were also 

greatly reduced by dazomet fumigation (table 3). 

Trichoderma spp. were lower in plots treated 

with Brassica green manure crops compared to 

pre-treatment levels. However, populations 

increased in fallowed plots and those treated 

with sewage sludge and steam. The ratios of 

Trichoderma to Fusarium populations indicated 

the most desirable values (highest numbers) for 

the fallow and steam treated plots (table 4). In 

general, the higher the ratio, the more potential 

for populations of Trichoderma to limit disease 

development by resident Fusarium populations. 

Pythium populations were greatly reduced by 

dazomet fumigation and somewhat reduced by 

steam treatment and the plastic tarping of a 

Brassica green manure crop (table 5). The only 

treatments that resulted in population levels of 

concern (near 100 cfu/g) by the time of sowing 

were the sewage sludge and Brassica green 

manure crop without tarping. 

Glucosinolate concentrations in B. juncea tissue 

samples did not differ among the treatments 

(table 6). The dominant glucosinolate contained 

in plant tissues was 2-propenyl. 

The lowest first-year seedling density was 

consistently found in plots treated with 

composted sewage sludge (table 7); much of the 

lack of seedling establishment may have been 

due to pre-emergence damping-off since little 

post-emergence mortality was noted in these 

plots. All the other treatments resulted in 

approximately equal 1-0 seedling densities; 

highest first-year mortality was obtained in plots 

treated with Brassica green manure crops (table 

7). 

The lower seedling density in composted 

sewage sludge treatments extended into the 

second seedling growing season (table 8). 

Highest seedling densities were found in the 

dazomet fumigated plots, but the other 

treatments, particularly the fallow, steam and 

Brassica green manure/no tarp treatments, were 

only slightly less. 

Seedling size was directly proportional to 

density, i.e., low-density stands (composted 

sewage sludge treatment) resulted in 

significantly larger seedlings (table 9). Taller 

seedlings were also produced in dazomettreated plots; significantly taller seedlings were 

produced in fallow and steam-treated plots 

compared to those produced in some of the 

Brassica green manure plots. 
7 

Table 1. Effects of selected pre-plant soil treatments on soil populations of Fusarium at the USDA Forest 

Service Nursery, Coeur d’Alene, Idaho. 

Colony-forming Units/g Oven-dry soil1 Treatment 

Pre-Treatment Post-Treatment Pre-Sowing 

Dazomet 287 [68-685] 7 [0-68] 13 [0-133] 

Fallow/Cultivation 382 [68-819] 352 [68-819] 495 [67-1203] 

Mustard/No Tarp 335 [68-755] 7583 [1489-19210] 10170 [5283-12572] 

Mustard/Tarp 830 272-1904] 7579 [1912-17480] 9593 6413-12025] 

Sewage Sludge 371 [275-412] 326 [68-952] 1244 [134-2675] 

Steam 408 [204-749] 287 [409-2866] 280 [0-1069] 

1 Values in bold are means; ranges are in brackets; means are from 5 replicate plots per treatment. 

Table 2. Fusarium species isolated from soil during assays of populations at the USDA Forest Service 

Nursery, Coeur d’Alene, Idaho. 

Number of Colonies Assayed1

Fusarium 

Species 

Pre-Treatment Post-Treatment Pre-Sowing All Samples 

F. oxysporum 253 [95.8] 1725 [97.4] 2408 [99.1] 4386 [98.2] 

F. solani 1 [0.4] 0 6 [0.2] 7 [0.2] 

F. equiseti 0 31 [1.7] 0 31 [0.7] 

F. avenaceum 9 [3.4] 11 [0.6] 0 20 [0.4] 

F. acuminatum 1 [0.4] 1 [0.1] 5 [0.2] 7 [0.2] 

F. sambucinum 0 3 [0.2] 5 [0.2] 8 [0.2] 

F. culmorum 0 0 6 [0.2] 6 [0.1] 

Totals 264 1771 2430 4465 

1 Percentages are within brackets.

Table 3. Effects of selected pre-plant soil treatments on soil populations of Trichoderma at the USDA 

Forest Service Nursery, Coeur d’Alene, Idaho. 

Colony-forming Units/g Oven-dry soil1 Treatment 

Pre-Treatment Post-Treatment Pre-Sowing 

Dazomet 2550 [953-6855] 14 [0-136] 7 [0-67] 

Fallow/Cultivation 3429 [546-6494] 3904 [1422-6987] 6316 [1537-12028] 

Mustard/No Tarp 1990 [1156-4395] 3085 [815-8349] 428 [67-1939] 

Mustard/Tarp 1442 [748-3808] 464 [341-683] 508 [0-1269] 

Sewage Sludge 2486 [1236-5287] 2584 [1224-3672] 3450 [1471-7757] 

Steam 1606 [544-2927] 1515 [409-2866] 2044 [200-3406] 

1 Values in bold are means; ranges are in brackets; means are from 5 replicate plots per treatment.
8 

Table 4. Effects of selected pre-plant soil treatments on ratios of Trichoderma to Fusarium populations at 

the USDA Forest Service Nursery, Coeur d’Alene, Idaho. 

Trichoderma/Fusarium Ratio1 Treatment 

Pre-Treatment Post-Treatment Pre-Sowing 

Dazomet 8.95 2.0 0.50

Fallow/Cultivation 8.97 12.24 13.77

Mustard/No Tarp 5.95 0.52 0.04

Mustard/Tarp 1.74 0.06 0.05

Sewage Sludge 6.70 7.93 2.77

Steam 3.94 5.28 7.30

1 The higher the value the more potential the soil has for disease suppressiveness. 

Table 5. Effects of selected pre-plant soil treatments on soil populations of Pythium at the USDA Forest 

Service Nursery, Coeur d’Alene, Idaho. 

Colony-forming Units/g Oven-dry soil1 Treatment 

Pre-Treatment Post-Treatment Pre-Sowing 

Dazomet 123 [68-212] 0 [0] 1 [0-13] 

Fallow/Cultivation 87 [55-164] 43 [7-224] 53 [0-140] 

Mustard/No Tarp 100 [14-163] 72 [0-285] 92 [0-260] 

Mustard/Tarp 107 [54--184] 32 [7-55] 44 [0-80] 

Sewage Sludge 117 [75-144] 53 [20-82] 103 [40-194] 

Steam 101 [75-136] 25 [7-61] 31 [0-67] 

1 Values in bold are means; ranges are in brackets; means are from 5 replicate plots per treatment.

Table 6. Average glucosinolate concentrations in B. juncea plants used as a green manure crop at the 

USDA Forest Service Nursery, Coeur d’Alene, Idaho. 

Glucosinolate Tissue Concentration (μmol/g) 

2-propenyl 35.24 

3-butenyl 0.46 

Phenylethyl 0.50 

3-indolymethyl 0.11 

1-methoxy-3-indolymethyl 0.07 

4-OH-3-indolylmehtyl 0.12 

4-methoxy-3-indolymethyl trace 
9 

Table 7. Effects of selected pre-plant soil treatments on density and mortality of 1-0 Douglas-fir seedlings 

at the USDA Forest Service Nursery, Coeur d’Alene, Idaho.1

Treatment Live Seedling Density Dead Seedling Density 

Dazomet 97 [75-145] 1 [0-5] 

Fallow/Cultivation 92 [51-135] 3 [0-14] 

Mustard/No Tarp 90 [61-123] 10 [0-19] 

Mustard/Tarp 85 [41-108] 12 [0-8] 

Sewage Sludge 55 [33-108] 3 [0-8] 

Steam 88 [65-128] 1 [0-8] 

1 Values in bold are means; ranges are in brackets. Density based on number of seedlings within subplots 

measuring 0.5m2 located within each replicate plot.

Table 8. Effects of selected pre-plant soil treatments on density of 2-0 Douglas-fir seedlings at the USDA 

Forest Service Nursery, Coeur d’Alene, Idaho.1

Treatment Live Seedling Density 

Dazomet 28.4 [25.1-32.2] 

Fallow/Cultivation 24.9 [21.3-28.6] 

Mustard/No Tarp 25.4 [19.6-30.3] 

Mustard/Tarp 21.6 [16.8-23.6] 

Sewage Sludge 19.1 [14.1-26.1] 

Steam 24.8 [22.7-26.9] 

1 Values in bold are means; ranges are in brackets. Density based on number of seedlings per 0.32m with bed 

widths of 1.12m and 7 rows of seedlings.

Table 9. Effects of selected pre-plant soil treatments on height, diameter, and root mass of 2-0 Douglasfir seedlings at the USDA Forest Service Nursery, Coeur d’Alene, Idaho1

. 

Treatment Height2 Diameter3 Root Mass4 

Dazomet 23.8 A 4.7 A 1.42 A 

Fallow/Cultivation 21.7 B 4.6 A 1.48 A 

Mustard/No Tarp 20.1 C 4.4 A 1.25 A 

Mustard/Tarp 21.6 BC 4.6 A 1.44 A 

Sewage Sludge 35.6 D 6.9 B 2.76 B 

Steam 21.6 BC 4.8 A 1.48 A 

1 Based on measuring 50 seedlings per replicated plot for each treatment. Means followed by the same capital 

letter are not significantly different (P=0.05) using LSD.

2

. Measured from the groundline to the tip of the terminal bud (cm).

3

. Measured just above the groundline (mm).

4

. Based on oven-dry weight of roots at lifting (g).
10 

DISCUSSION 

Preplant soil fumigation with wide-activity 

biocides used in forest seedling nurseries for 

many years. This has usually resulted in 

production of high-quality seedlings, but has 

also required continued reliance on this 

expensive procedure. Because fumigants are 

not selective in their target microorganisms 

(Boone 1988; Boyd 1971, James 1989), 

beneficial as well as detrimental organisms are 

equally affected. Re-invasion of fumigated soil 

by pathogens instead of saprophytes may result 

in greater disease severity than if no fumigation 

had been done (Marois et al. 1983; Vaartaja 

1967). When fumigation is curtailed or 

terminated, it may take several years before soil 

is capable of producing high-quality seedling 

crops unless disease-suppressive amendments 

(composted organic amendments, biological 

control agents) are added (Gouin 1993; 

Papavizas 1985). Fallowing fields may reduce 

pathogen populations (Hamm and Hansen 1990; 

Hansen et al. 1990; James and Beall 2000; 

Stone et al. 1995), but will generally not 

eliminate them like chemical fumigation. The 

transition from routine pre-plant soil fumigation 

to non-fumigation may be difficult, particularly if 

fields cannot be fallowed for several years 

and/or the proper combination of organic 

amendments are not available. 

Brassica spp. may help bridge the transition 

from fumigation to non-fumigation. Certain 

cultivars have shown high toxicity to common 

soilborne plant pathogens (Mayton et al. 1996) 

and may exhibit disease-suppressive 

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); these 

isothiocyanates may be toxic to certain soil 

microorganisms, particularly at high 

concentrations. However, populations of 

Fusarium spp. tend to increase, sometimes 

dramatically, whenever plant organic matter is 

added to soil (Hamm and Hansen 1990; Hansen 

et al. 1990; James et al. 1996; Wall 1984). 

Response to organic matter may outweigh any 

potential toxicity that may be introduced when 

Brassica crops are incorporated into soil (Hamm 

and Hansen 1990; Hansen et al. 1990). This 

apparently happened in the current evaluation. 

Fusarium populations increased dramatically 

after incorporation of the Brassica crop into soil. 

In addition, enough of this high population was 

comprised of pathogenic isolates to result it 

increased seedling mortality, particularly during 

the first growing season when most root disease 

mortality occurs (James 2001, 2002). By the end 

of the two-year crop cycle, seedling densities 

were less and seedlings somewhat shorter than 

those in fumigated plots. Therefore, it appeared 

that incorporating green Brassica juncea 

residues into soil as a biofumigant and added 

source of organic matter was not as effective as 

standard dazomet fumigation and did not 

improve seedling production. Perhaps other 

Brassica cultivars may perform better under 

forest nursery conditions and produce sufficient 

toxic metabolites to overcome stimulation of 

pathogen populations by the added organic 

matter. 

We previously showed that 2-propenyl 

isothiocyanate was the most effective of six 

isothiocyanates tested against several forest 

nursery isolates of F. oxysporum (Smolinska et 

al. 2003), the most prevalent soilborne pathogen 

at the Coeur d’Alene Nursery (James et al. 

1990, 1996). Bioassays conducted with 2-

propenyl isothiocyanate in volatile form inhibited 

mycelial growth and completely suppressed 

condial and chlamydospore germination of the 

pathogen. Therefore, a B. juncea variety with 

high 2-propenyl glucosinolates concentrations 

was selected for our studies. Lack of F. 

oxysporum control may have been due to 

inefficient release of isothiocyanate from 

decomposing plant tissues, a key step that 

requires extensive maceration of tissues and 

ample water (Morra and Kirkegaard 2002). 

Ensuring efficient isothiocyanate release from 

Brassica tissues is critical since organic carbon 

inputs without effective control of soilborne 

pathogens is common (Hansen et al. 1990; 

Hamm and Hansen 1990; James et al. 1996). 

No beneficial effects were found when 

Trichoderma harzianum was added to some 

treatments. This fungus has been an effective 

suppressor of soilborne pathogens (Knudsen 
11 

and Bin 1990; Knudsen et al. 1991) and should 

help reduce disease severity when incorporated 

into seedling management regimes. However, in 

our evaluation, it is possible that the large 

increases in potential pathogen populations 

resulting from incorporating organic matter into 

soil may have outweighed any potential benefit 

of adding T. harzianum inoculum. This biocontrol 

agent may have greater potential when applied 

next to sown seed, particularly in fields that have 

been fallowed or otherwise not amended with 

organic matter. Further tests should evaluate 

this potential. 

Composted sewage sludge amendments 

resulted in greatly reduced seedbed densities, 

although surviving seedlings were much larger 

than those from other treatments. This type of 

compost has proven effective in reducing 

soilborne diseases in the past (Gouin 1993), 

although accumulation of soluble salts from such 

composts may result in phytotoxicity of some 

crops (Gouin 1977) 

Steam treatment of soil has potential as an 

effective alternative to chemical fumigation 

(Karsky and Trent 2000). However, currently 

available application equipment requires high 

energy inputs and takes much too long to 

effectively treat sufficient volumes of soil for 

operational use. Further refinements will be 

necessary for steam applications to effectively 

compete with existing preplant chemical soil 

fumigation. 

In conclusion, the various pre-plant soil 

treatments tested in this evaluation were not as 

effective as standard dazomet fumigation which, 

is routinely used at the Coeur d’Alene Nursery. 

Brassica crop amendments were generally 

ineffective in this test. Problems associated with 

Brassica crop production prior to incorporation 

into soil occurred. The crop grew quickly and 

produced mostly above-ground biomass and 

little root mass before it required incorporation 

into soil because of flowering. If greater root 

production had occurred, perhaps our results 

would have been different. Future tests should 

evaluate additional cultivars, including those 

known to produce higher levels of 

glucosinolates. Greater root development with 

less overall biomass production is desired to 

enhance the ability of Brassica crops to act as 

effective biofumigants. 

LITERATURE CITED 

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

Desmarchelier. 1994. Biofumigation: 

isothiocyanates released from Brassica roots 

inhibit growth of the take-all fungus. Plant and 

Soil 162:107-112. 

Boone, A.J. 1988. Soil fumigation in forest tree 

nurseries. Proceedings of the Southern 

Forest Nursery Association – 1988. pp. 33-

38. 

Boyd, R.J. 1971. Effects of soil fumigation on 

production of conifer nursery stock at two 

northern Rocky Mountain nurseries. USDA 

Forest Service, Intermountain Forest & 

Range Experiment Station. Research Paper 

INT-91. 19p. 

Chapman, W. 1992. Alternative treatments to 

methyl bromide. Proceedings of the Southern 

Forest Nursery Association – 1992. pp. 96-

103. 

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

Fisher, N.L., L.W. Burgess, T.A. Toussoun, 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, V. Borek. 1999. Allelochemicals 

released in soil following incorporation of 

rapeseed (Brassica napus) green manures. 

Journal of Agricultural and Food Chemistry 

47:3837-3842. 

Gouin, F.R. 1977. Conifer tree seedling 

response to nursery soil amended with 

composted sewage sludge. HortScience 

12:341-342. 
12 

Gouin, F.R. 1993. Utilization of sewage sludge 

compost in horticulture. HortTechnology 

3(2):161-163. 

Hansen, E.M., D.D. Myrold, 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., 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. 

Ibarbia, E.Z. 1995. Fundamentals of fumigation. 

Greenhouse Grower 13(1):141-142, 144. 

James, R.L. 1989. Effects of fumigation on soil 

pathogens and beneficial microorganisms. In: 

Landis, T.D. (tech. coord.). Proceedings: 

Intermountain Forest Nursery Association 

Meeting. USDA Forest Service, Rocky 

Mountain Forest and Range Experiment 

Station. General Technical Report GTR-184. 

pp. 29-34. 

James, R.L. 2001. Root disease of 1-0 bareroot 

Douglas-fir seedlings – USDA Forest Service 

Lucky Peak Nursery, Boise, Idaho. USDA 

Forest Service, Northern Region, Forest 

Health Protection. Nursery Disease Notes 

#144. 10p. 

James, R.L. 2002. Root disease of 1-0 bare root 

ponderosa pine seedlings – Lone Peak 

Nursery, Draper, Utah. USDA Forest Service, 

Northern Region, Forest Health Protection. 

Nursery Disease Notes #147. 8p 

James, R.L., K. Beall. 1999. An evaluation of the 

effects of dazomet on soil-borne diseases 

and conifer seedling production - USDA 

Forest Service Lucky Peak Nursery, Boise, 

Idaho. USDA Forest Service, Northern 

Region, Forest Health Protection. Report 99-

9. 15p. 

James, R.L., 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., R.K. Dumroese, D.L. Wenny. 1991. 

Fusarium diseases of conifer seedlings In: 

Sutherland, J.R., S.G. Glover (eds.). 

Proceedings of the First Meeting of IUFRO 

Working Party S2.07-09 (Diseases and 

Insects in Forest Nurseries). Forestry 

Canada. Pacific and Yukon Region. 

Information Report BC-X-331. pp. 181-190. 

James, R.L., S. Metzger, 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, 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. 

Karsky, D., A. Trent. 2000. Nusery soil steam 

fumigation. USDA Forest Service, 

Technology & Development Program, 

Missoula, Montana. 16p. 

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., L. Bin. 1990. Effects of 

temperature, soil moisture, and wheat bran 

on growth of Trichoderma harzianum from 

alginate pellets. Phytopathology 80:724-727. 
13 

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

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

and sporulation of pelletized biocontrol fungi. 

Applied and Environmental Microbiology 

57:2864-2867. 

Linderman, R., W. Dixon, S. Fraedrich, R.S. 

Smith, Jr. 1994. Alternatives to methyl 

bromide: assessment of research needs and 

priorities for forestry, nursery, and ornamental 

crops. Tree Planters' Notes 45:43-47. 

Marois, J.J., M.T. Dunn. G.C. Papavizas. 1983. 

Reinvasion of fumigated soil by Fusarium 

oxysporum f.sp. melonis. Phytopathology 

73:680-684. 

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

1996. Correlation of fungicidal activity of 

Brassica species with allyl isothiocyanate 

production in macerated leaf tissue. 

Phytopathology 86:267-271. 

Miller, W.O., M.G. Norris. 1970. A new review of 

soil fumigation practices for use in forest 

nurseries. Down to Earth 26(3):9-12. 

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

Isothiocyanate release from soil-incorporated 

Brassica tissues. Soil Biology & Biochemistry 

34:1683-1690. 

Nelson, P.E. T.A. Toussoun, 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., 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., P.M.F. Rodrigues. 1999. Towards 

a more sustainable agriculture system: The 

effect of glucosinolates on the control of soilborne 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. 

Smith, R.S., Jr., R.V. Bega. 1966. Root disease 

control by fumigation in forest nurseries. Plant 

Disease Reporter 50:245-248. 

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

Vaartaja, O. 1967. Reinfestation of sterilized 

nursery seedbeds by fungi. Canadian Journal 

of Microbiology 13:771-776. 

Wall, R.E. 1984. Effects of recently incorporated 

organic amendments on damping-off of 

conifer seedlings. Plant Disease 68:59-60. 

Waterhouse, G.M. 1968. The genus Pythium 

Pringsheim. Commonwealth Mycological 

Institute, Kew, Surrey, England. Mycological 

Papers No. 110. 70p. 

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. 
14 

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. M.J. Morra and G.R. Knudsen are with the Soil Science Division, University of 

Idaho, Moscow 83844-2339; email (M.J. Morra): mmorra@uidaho.edu; (G.R. Knudsen): 

microbes@moscow.com