Transcript Fungicide effects on Sclerotinia rot of lettuce

The New Zealand Institute for Plant & Food Research Limited
Fungicide effects on
Sclerotinia rot of lettuce
Peter Wright and Robert Beresford
Sclerotinia rot – White mold – ‘Drop’
• Caused by the fungi Sclerotinia minor
(Sm) and S. sclerotiorum (Ss)
• Serious pathogens of several other
horticultural crops
• Soilborne pathogens - can survive in
soil as sclerotia for >3 years
• Infect plants by hyphal germination of
sclerotia that are in contact with
senescing lower leaves on the soil
surface (Ss & Sm)
• Infect plants by airborne ascospores,
which infect senescent or dead lettuce
leaves (Ss) (see apothecia in photo ->)
The New Zealand Institute for Plant & Food Research Limited
Sclerotinia rot – White mold – ‘Drop’
• All commercial cultivars of lettuce are susceptible to both
Sclerotinia species
• Fungicides are the primary method of disease control (others
include bio-control agents, crop rotation and soil amendments)
• The only chemical currently registered in NZ for control of
Sclerotinia rot of lettuce is the benzimidazole fungicide carbendazim
• Benzimidazoles are generally at high risk for development of
fungicide resistance
The New Zealand Institute for Plant & Food Research Limited
Fungicide resistance
• Sclerotinia isolates may be developing resistance to some
fungicides – including carbendazim
• Resistance arises from repeated use of an at-risk fungicide – the
fungus changes genetically allowing it to survive in the presence of
the fungicide
• Resistance development can be slowed by limiting use of the atrisk fungicide groups through a resistance management strategy
• When resistance develops, local data are required to scope the
problem and to develop a strategy tailored to the local situation.
The New Zealand Institute for Plant & Food Research Limited
Fungicides to control Sclerotinia in NZ
Product
Carbendazim
Topsin M-4A
Sumisclex 500SC
Fluazanim
Iprodione
Taratek 5F
Chlorocarb
Pristine
Flint
Chemical Group
Benzimidazole
Benzimidazole
Dicarboximide
Dicarboximide
Dicarboximide
Nitrile & benzimidazole
Nitrile & benzimidazole
Carboxamide & strobilurin
Strobilurin
Crop
Lettuce, bean, tomato
Bean, tomato
Bean, cucurbit, tomato
Potato, tomato
Ornamentals, kiwifruit
Bean, tomato
Tomato
Kiwifruit
Kiwifruit
The New Zealand Institute for Plant & Food Research Limited
Fungicides to control Sclerotinia in lettuce overseas
Chemical
Fungicide Group
Boscalid
Iprodione
Vinclozolin
Procymidone
Carboxamide (7)
Dicarboximide (2)
Dicarboximide (2)
Dicarboximide (2)
Anilinopyrimidine (9)/
Phenylpyrrole (12)
Aromatic hydrocarbon (14)
Triazole (3)
Benzimidazole (1)
Cyprodinil/Fludioxonil
Dichloran
Tebuconazole
Carbendazim
Possible
resistance
issues?
yes
Yes
Yes
Yes
Yes
Yes
Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC)
according to different modes of actions. Fungicides with a different group number are
suitable to alternate in a resistance management program.
The New Zealand Institute for Plant & Food Research Limited
Fungicide resistance methodology
Disease
controlled
Fungicide applications
Disease not
controlled
Fungus
Sensitive
Fungus
Resistant
Decreasing sensitivity
Low EC50
Increasing resistance
High EC50
EC50= Effective concentration of fungicide that gives 50% inhibition
(Fungus tested at different fungicide concentrations)
The New Zealand Institute for Plant & Food Research Limited
EC50= Effective concentration of fungicide
that gives 50% inhibition of the fungus
The New Zealand Institute for Plant & Food Research Limited
Growth of Mycelium in Fungicide-amended
media
The New Zealand Institute for Plant & Food Research Limited
Inhibition of mycelial growth of S. sclerotiorum on PDA
containing fungicide
Radial growth (mm) of
mycelium each 24 hours
16
14
Carbendazim
12
10
Dichloran
Trifloxystrobin
8
Tebuconazole
6
Iprodione
4
2
Procymidone
0
0.1
0.5
1
5
10
Fungicide concentration (ppm)
The New Zealand Institute for Plant & Food Research Limited
Nation-wide survey
• Nation-wide survey to determine S. sclerotiorum and S.
minor sensitivity to several fungicides.
• S. minor and S. sclerotiorum isolates used in this study will
originate from mycelium from a single sclerotium of each
fungal species taken from naturally infected lettuce leaves.
• Laboratory assay – growth of Sclerotinia isolates on
fungicide-amended media.
• If/when resistance has occurred we can look at developing
disease control strategies tailored to the local situation.
The New Zealand Institute for Plant & Food Research Limited
To collect Sclerotinia isolates (sclerotia) for me
for my fungicide resistance tests
The New Zealand Institute for Plant & Food Research Limited