Fate of Elm Diseases in Municipal Composting

The Fate of Elm
Diseases in a
Municipal
Composting
Environment

PROJECT OVERVIEW
 Goal:
 To determine whether or not elm diseases are
destroyed during composting

 Implication:
 Determine whether or not diseased
wood must be kept out of compost
feedstocks

PRESENTATION OVERVIEW

 Project Background & Objectives
 Procedures – Inoculation
Experiments and Composting
Trials
 Composting Trials - Results
 Summary and Recommendations

BACKGROUND – PROJECT IMPETUS
 Edmonton’s Gore composter processes
biosolids and wood chips
 Parks Branch provides clean green wood
 Diseased wood from Forestry is diverted to
landfill
 Reduces risk of
disease spread
 Parks Branch is a
major consumer of
Gore compost

BACKGROUND – PROJECT IMPETUS
 Possibility of diverting a portion of
Forestry’s diseased wood from the
landfill.
 There are other contributors of wood to the
Gore process
 Not necessarily screened
 Need to determine the fate of some
common local plant diseases during
composting

BACKGROUND – SOME COMMON
DISEASES
 Dothiorella ulmi
 D. ulmi-infected elm
makes up the majority of
landfilled wood

 Verticillium dahliae
and V. albo-atrum
 Have been isolated from
elm in Edmonton area
 Have wide host ranges

LITERATURE REVIEW
 Plant pathogens can be inactivated by
exposure to heat
 Heat tolerance varies by organism and form
 No time-temperature guidelines for plant
pathogens in North America
 Human pathogens: 55oC for 3 days

LITERATURE REVIEW
 Verticillium dahliae
 Eliminated in small-scale composter when material
turned, Tmax ≈ 70oC, and T > 50oC for 10-14 days
 V. albo-atrum & Dothiorella ulmi
 Nothing in the literature
 D. ulmi laboratory incubation tests suggest that
typical composting temperatures should
be adequate
 Fungi and fungi-like species
 Some species survived T > 55oC

SPECIFIC OBJECTIVES
 Determine to what degree D. ulmi, V.
dahliae, and V. albo-atrum are inactivated
by time-temperature conditions in Gore
composter.
 How likely is it that these organisms will be
eradicated in the Gore composter?
 Does diseased wood need to be diverted from
the composter?

OVERALL EXPERIMENTAL PLAN
 Wood chip inoculation experiments
 Place bagged infected wood chips in the
Gore system during the high-temperature
phase
 Periodically recover bags and evaluate
pathogen survival in composted
elm wood

PROCEDURES - WOOD CHIP
INOCULATION
 Wood chip inoculation procedure optimized
 Inoculum prepared from fungal cultures
 Wood chips sterilized by autoclaving, then
sprayed with inoculum and agar plugs placed
 Incubated for 26 days at 22°C

Verticillium
Dothiorella ulmi albo-atrum

Control Verticillium dahliae

PROCEDURES – SAMPLE
PREPARATION
 Infested wood chips sealed in sterilized
Ziploc bags (with air space).
 Organisms affected by temperature only.
 Ziplocs placed into nylon mesh bags
 “Sample bundles” created
 One bag for each organism,
plus a temperature probe.

PROCEDURES – SAMPLE PLACEMENT

PROCEDURES – SAMPLE PLACEMENT

(October 13 2009)

PROCEDURES – SAMPLE
COLLECTION AND TESTING
 Sample bundles and compost samples
collected periodically
 Every day or two for first week, and weekly or
biweekly thereafter.
 Wood chips tested for pathogen survival
 Temperature data examined

RESULTS – TEMPERATURE
Pile construction/
sample insertion Pile completion

80
Ambient
X1 AVG.
70
X2
X3
60
X4
X5
50
X6
Temperature (oC)

X7
40
On-Site (~0.8m deep)
On-Site (~0.2m deep)
30

20

10

0

-10
0 7 14 21 28 35 42

Time (days)

RESULTS – PATHOGEN SURVIVAL VS.
TEMPERATURE
Sample Location
X1 X2 X3 X4 X5 X6 X7
≥ 70 °C 0 0 0 0 0 0 8.7
Total amount ≥ 65 °C 0 0 0 0 0 0 11.2
of time ≥ 60 °C 0 0 0 0 0.8 0 13.7
(days) that ≥ 55 °C 0 0 0 0 2.6 3.2 21.5
various ≥ 50 °C 0 0 0 0 12.3 16.0 35.6
temperatures ≥ 45 °C 0 0 0 7.1 20.3 26.5 39.7
were ≥ 40 °C 0 0 5.5 11.1 26.1 30.0 39.9
exceeded ≥ 35 °C 0 0 11.7 17.6 34.4 38.5 40.0
≥ 30 °C 0 0 21.3 30.1 38.6 38.9 40.1
Pathogen D. ulmi + + - - - - -
survival at V. albo-
end of atrum + + - - - - -
composting V. dahliae + + - - - - -

RESULTS – PATHOGEN SURVIVAL VS.
TEMPERATURE
 Bags at locations where pathogen
destruction was seen were compressed.
 Testing was done at room temperature in
compressed (anoxic) bags
 Pathogens survived anoxic conditions

CONCLUSIONS
 Appears that D. ulmi, V. albo-atrum, and V.
dahliae will be inactivated if temperatures
exceed 40°C for more than 5.5 days.
 Likely to occur in interior of pile; perhaps not in
outer layer.
 Important to ensure that all materials from
exterior zones in Stage 1 get mixed into higher
temperature zones in subsequent stages.
 May not need to divert diseased wood to
landfill.

RECOMMENDATIONS
 Repeat trial 2x more, with modifications to
improve procedures, e.g.
 Better sorting of wood chips
 Use of rigid sample containers

 Study temperature profiles in Gore Stages 2
and 3 (curing) in detail
 Potential small-scale reactor study
 Pinpoint time-temperature requirements
 Determine suitable indicator organisms

CONTACT INFO

Kristine Wichuk
kwichuk@ualberta.ca

Daryl McCartney
daryl.mccartney@ualberta.ca

RESULTS – COMPOST
 Pathogen survival not affected directly by
MC, pH, or C:N
 MC : ~53% to ~62% at start
~32% to 55% at end
 pH : ~7.6 to ~7.8 at start
~7.3 to ~8.4 at end
 C:N: varied throughout pile at start and end

RESULTS – PATHOGEN SURVIVAL

X2, Day 42

X7, Day 42

D. ulmi V. dahliae V. albo-atrum

Fate of Elm Diseases in Municipal Composting

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