O26 Webber
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Persistence of Phytophthora kernoviae and P. ramorum on
infested sites: impact on disease management
3rd International Phytophthora Workshop
Joan Webber, Forest Research
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P. kernoviae / P. ramorumBoth apparently introduced invasives in BritainBoth aerial Phytophthoras which cause foliar/shoot symptoms on rhododendronRhododendron is the UK ‘bay laurel’Both cause bleeding lesions on trees, mainly beech (Fagus sylvatica)Both thrive under similar climatic regimes typical of Cornwall in south west England, so the majority of outbreaks are there
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Disease outbreaks: 2002/03 - 08England, Scotland and Wales
279 (70*)615 (501*)Total55 (2*)4 (3*)P. kernoviae
224 (68*)611 (498*)P. ramorum
Managed/ unmanaged
Nurseries/ retail plant sales
Pathogen
Data derived from Defra Consultation document 2008
* eradicated outbreaks
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Distribution of Pk
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Distribution of Pr
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Current measures in the UK
• EU emergency measures apply to Pr– eradication of infection in nurseries– containment/eradication of infection in
natural and semi-natural environments• Similar measures apply to Pk
– containment or eradication via the removal of infected understorey plants as the majority of outbreaks are in woodlands with a dense understorey of R. ponticum
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Impact of rhododendron eradication over 1-3 years
• Time frame for persistence in naturally infected leaves of rhododendron?
• Persistence in litter and soil?• Regrowth and re-infection of the
rhododendron?
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How long does inoculum persist?
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Persistence of Pkinoculum
Naturally infected leaves put into bags and air suspended or put in litter layer
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Survival of Pk in naturally infected leaves: 2005 - 06
0102030405060708090
100
0 1 2 3 4 5 6 8 12
Month
% le
aves
with
Pk
Air exposed Litter embedded
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Deterioration of leaves over in the litter layer
3 months 9 months
12 months6 months
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Survival of Pk in naturally infected leaves: 2006 - 07
0102030405060708090
100
0 1 2 3 4 6 8 10 12
Months
% le
aves
with
Pk
Air exposed Litter embedded
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05
1015202530354045
0 1 2 3 4 6 8 10
Months
% re
cove
ry
P. kernoviae P. citricola
Survival of Phytophthora in naturally infected leaves: 2006 - 07
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Survival of Pr in naturally infected leaves: 2006 - 07
0102030405060708090
100
0 1 2 3 4 6 8 10 12
Months
% le
aves
with
P. r
amor
um Air exposed Litter embedded
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Pre and post R. ponticum removal in a Pkinfested woodland
0
10
20
30
40
50
60
70
80
Pre-treatment(Sept '04)
Post-treatment (Sept '05)
Post-treatment(Sept ’07)
Perc
ent P
k po
sitiv
e sa
mpl
es Litter Soil
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◄ Re-sprouting from rhododendron stumps with infection
What happens to inoculum………
Recruitment of new ►rhododendron seedlings
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Seedling Foliage Soil Roots123456789101112131415161718192021222324252627282930
Fichtner et al., 2008: APS
Impact of persistent Pk inoculum on rhododendron recruitment
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Conclusions• Both Pr and Pk are proving to be difficult to
eradicate from infected natural or semi- natural environments– eradication process must involve litter removal– but persistence is extended and signs of disease by
Pk return after more than 3 yr following eradication– additional issue of asymptomatic infection of
rhododendron roots by Pk• Is it worthwhile?
– removing the infected rhododendron does safeguard trees in woodlands from Pk infection
– reduces inoculum and therefore likely to reduce the opportunities for Pk to get into the nursery trade
– consultation on ‘is it worthwhile’? www.defra.gov.uk/corporate/consult/phytophthora-ram-kern/index.htm