Disease Control Products for
Stored Potatoes
Jill Thomson and
Doug Waterer
Dept of Plant Sciences,
University of
Saskatchewan
Control of Storage Diseases
• Challenge - need dependable
control of various diseases
during storage/handling
• Challenge - need safe,
affordable products
• Challenge - products must be
readily applied with available
equipment
Control of Storage Diseases
• Traditional options
– Mertec (TBZ)
•
•
•
•
•
spray applied during load-in
good coverage critical
not effective against bacteria
not effective against Late Blight
extensive resistance in Dry Rot
and Silver scurf
• $ 6.40/tonne at CDN label rate
Control of Storage Diseases
• Available options
– Dithane (Mancozeb)
•
•
•
•
spray applied during load-in
good coverage critical
not effective against bacteria
effective against Dry Rot and
Silver scurf
• $ 11.06/tonne
• only registered for use on seed
Control of Storage Diseases
• Alternate options
– Purogene
– Oxidate
– Ozone
Control of Storage Diseases
• Purogene (Anthium)
– UAP
– Sodium chlorite + acid =
Chlorine dioxide (gas) + other
Cl species
– applied as spray to potatoes
going into storage and/or
– added to ventilation air
Control of Storage Diseases
• Purogene
– works by oxidation reactions
– label indicates effective against
L. blight, Silver Scurf, Dry Rot
and Bacterial Soft rot
– inactivated by soil
– no residual activity
– repeated or continuous
treatment recommended
Control of Storage Diseases
• Purogene - Status
– Researched by MSU, NDSU,
Idaho, MB and AB.
– 5th year of Class 18 Exemption
in U.S.
– Emergency use in Canada in
1999, 2000 and 2001 but not in
2002
Control of Storage Diseases
• Purogene Efficacy against Soft rot
– MB data
– some control
Soft Rot Control with
Purogene
100
80
%
60
Soft
40
Rot
20
0
0
50
100 400
PPM Purogene
Russets
Shepody 1
Shepody 2
Control of Storage Diseases
Effect of Purogene on the amount of rot found on tubers (MANITOBA)
Cultivar
Russet B.
Shepody
Shepody
Concentration Avg Rot per Tuber (%)
0
23.5
50
3.8
200
1.1
400
2.2
0
9.1
50
5.8
400
3.2
0
1.1
50
2.4
200
0.2
400
0.3
Control of Storage Diseases
• Purogene vs Late Blight
– MB data
– Tubers treated immediately after
inoculation
– some control
Control
Purogene
100
80
60
40
20
0
Trial 1
Trial 2
Trial 3
Trial 4
Control of Storage Diseases
• Purogene vs Rhizoctonia, Silver
Scurf, Soft Rot and Dry Rot
–
–
–
–
AB data
Tubers sprayed at load in
Tubers treated in storage (weekly)
minimal control
Control of Storage Diseases
• Purogene - Safety
– mixing step requires safety
equipment (ClO2 vapors)
– ventilate storage for 2 h prior to
re-entry
– potatoes must be washed prior
to consumption
– slowly corrodes copper, brass,
aluminum
Control of Storage Diseases
• Purogene - Economics
– 16-32 ml/ton applied at load-in
– max rate of 16 ml/ton/month
applied during storage
humidifaction
– $25/L
– $ 2.50/ton for pre-treatment +
continuous application over 5
months
Control of Storage Diseases
• Purogene Conclusions
– variable results
– problems getting full activation
– problems with inactivation by
soil
– problems with uniformity of
distribution of effective dosages
– problems with adding humidity
to problem storages
– relatively safe and affordable
Control of Storage Diseases
• Oxidate
– BioSafe
– Hydrogen Peroxide + acetic
acid
– applied as spray to potatoes
going into storage and/or
– added to ventilation air
Control of Storage Diseases
• Oxidate
– works by oxidation reactions
– label indicates effective against
L. blight, Silver Scurf, Dry Rot
and Bacterial Soft rot
– inactivated by soil
– no residual activity
– continuous treatment
recommended
Control of Storage Diseases
• Oxidate - Status
– approved in U.S. for use in wide
range crops in field and storage
– approved as an “organic” pesticide
– “Emergency Use” in BC and AB in
2002
– full registration anticipated for April
2003
– NB has done some testing in
potatoes
Control of Storage Diseases
• Oxidate - Efficacy
Control of Storage Diseases
• Oxidate - Efficacy
FDR development after Oxidate
treatment for 16 weeks
Average % dry
rot
25
20
15
Shepody
Norland
10
5
0
0
1%
2%
Oxidate treatment
Control of Storage Diseases
• Oxidate - Efficacy
Incidence silver
scurf (av.%)
Silver scurf development after Oxidate
treatment for 16 weeks
100
80
60
Shepody
Norland
40
20
0
0
1%
2%
Oxidate treatment
Control of Storage Diseases
• Oxidate - Efficacy
Soft rot development after Oxidate
treatment for 16 weeks
Soft rot (%)
5
4
3
2
Shepody
Norland
1
0
0
1%
2%
Oxidate treatment
Control of Storage Diseases
• Oxidate - Safety
– no mixing step
– concentrated product is
corrosive
– no re-entry restriction
– no limit to amount applied
– no requirement to wash prior to
consumption
– slowly corrodes copper, brass,
aluminum
Control of Storage Diseases
• Oxidate - Economics
– 1-2% solution applied to wetness at
load-in
– 1:100 to 1:300 applied during storage
humidifaction
– $17.78/L
– pre-treatment = $ 0.71-1.42/tonne
– 1% in humidification system = $1.78
per injection
– How many injections into system
over 5 month period?
Control of Storage Diseases
•
Oxidate – Conclusions
– potential to reduce disease
levels
– high dosages and continuous
application most effective
– safe and affordable
– need uniform delivery of
effective dosages
– adding humidity to problem
potatoes ?
– Impact on sprouting ??
Control of Storage Diseases
• Ozone
– various manufacturers
– O2 + high energy = O3 (gas)
– applied at high levels to
potatoes going into storage
and/or
– added to ventilation air
Control of Storage Diseases
• Ozone
– works by oxidation reactions
– lab studies indicates effective
against range of bacteria and
fungi
– inactivated by soil
– no residual activity
– continuous treatment
recommended
Control of Storage Diseases
• Generator unit, outside storage
Control of Storage Diseases
• Monitoring equipment mounted above
conveyor. Injection of O3 into conveyor
system, removal of excess O3.
Control of Storage Diseases
• Ozone - Status
– well established in other food
areas
– data for storage use is limited
– advantage = does not depend
on water for delivery (spray or
humidity)
Control of Storage Diseases
• Ozone – Efficacy
% Incidence
FDR on surface-inoculated tubers
80
70
60
50
40
30
20
10
0
OZONE
Control
1 day
1 wk
3 wks
Exposure time
Control of Storage Diseases
• Ozone – Efficacy
% Incidence
Silver scurf after ozone treatment
30
25
20
15
10
5
0
Ozone
Control
1 day
1 wk
3 wks
Exposure time
Control of Storage Diseases
• Ozone – Efficacy
– O3 applied loading into storage
20
15
10
Norland
Yukon Gold
5
O
zo
ne
M
er
te
c
D
ith
an
e
on
tr
ol
0
C
Extent of FDR
damage (sq.cm)
FDR development in wounded,
inoculated tubers
Control of Storage Diseases
• Ozone - Safety
– widely used to sanitize food and
buildings
– corrosive at high
concentrations
– exposure levels well
established
– no limit to amount applied
– no requirement to wash prior to
consumption
Control of Storage Diseases
• Ozone - Economics
– generators + power
– 500 ppm during loading
– 2 ppm during storage
ventilation
–$?
Control of Storage Diseases
• Ozone - Conclusions
– primarily provides contact
control
– most effective against surface
problems (scurf and bacteria)
– ineffective against aggressive
or well established infections
– economics ?
– Impact on product/facilities ?
Control of Storage Diseases
• Conclusions
– Purogene and Oxidate
demonstrated to provide some
control under certain conditions
– Ozone also shows potential
– Most effective against new,
surface problems
– Supplement to good harvest
and storage management
practices
Control of Storage Diseases
• In the future ?
– No new chemical products in
the pipeline
– BioCide is developing granular
products for time-release uses
– Help overcome short reaction
times of chlorine dioxide and
improve in-storage distribution
– Further out … Bacterial
antagonists to common
diseases