Management Strategies for Lettuce
Drop in Arizona and California
Lettuce Drop
Barry Pryor
Department of Plant Pathology
University of Arizona
The Pathogens:
Sclerotinia minor and S.
S. sclerotiorum
sclerotiorum
•
•
•
•
over 1500 recorded hosts
cottony rot, white mold, watery rot on
fruits, flowers, leaves, stems, and roots
growth is favored by moist conditions
both species produce longlong-lived resting
structures known as sclerotia
S. minor
Eruptive Germination
Lettuce drop
disease cycle
S. sclerotiorum
S. minor
1
Lettuce drop
disease cycle
Apothecium discharging
ascospores
Integrated disease
management of lettuce drop
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„
„
„
host resistance
cultural practices
chemical control
biocontrol
2
Host Resistance
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„
„
No commercially acceptable cultivar exist
Most breeding programs have focused on
Cultural Practices
„
S. minor
-“slow“slow-dying” phenotypes have been
described
Little progress has been made on
resistance to S. sclerotiorum
„
Crop rotation
-broccoli rotation for control of S. minor
-fallow rotation for control of S. sclerotiorum
Irrigation
water management is key to reduced disease
-furrow…sprinkler…subsurface drip
2003 Yuma Fungicide Trials
Chemical control of lettuce drop
Treatment
„
„
„
„
Rovral 4F
Ronilan 50DF
Endura 70WG
Serenade AS
Pristine 38WG
Botran 5F
Endura 70WG
Pristine 38WG
Botran 5F
Switch 62.5WG
Endura 70WG
Switch 62.5WG
Contans
Contans
Non-treated control
iprodione (Rovral)
Rovral)
vinclozolin (Ronilan)
Ronilan)
dicloran (Botran)
Botran)
boscolid (Endura)
Endura)
Rate
lb a.i./A
S. minor S. slerotiorum
1.0
1.0
0.35
4.0 qt prod.
0.4
1.87
0.45
0.45
3.75
0.43
0.35
0.56
4.0 lb prod.
2.0 lb prod.
--------
6.4
9.8
10.0
10.0
10.2
10.8
11.0
11.0
11.0
11.6
11.8
12.4
12.6
16.8
23.2
29.2
21.2
16.6
27.4
27.8
24.6
17.2
19.8
28.2
27.6
37.2
30.0
12.8
18.2
37.8
*each plot contained approx. 55 plants
Benefits of biocontrol strategies
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„
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complement other disease management
strategies
development of resistance unlikely
cost effective
few restrictions on use
worker and environmental safety
development of specialty markets
Objectives 20022002-2003
•
•
•
evaluate the efficacy of commercially
available biocontrol agents for the control
of lettuce drop
evaluate the survival of biocontrol agents
in the field
evaluate the sensitivity of biocontrol
agents to Botran,
Botran, Rovral,
Rovral, and Ronilan
3
120
100
100
40
20
0
80
60
40
20
0
Pla
Yuma S. Minor Trial 2003
Yuma S. Sclerotiorum Trial 2003
120
120
100
80
60
40
20
100
80
60
40
20
n
rd
ua
pa
nio
ilg
m
so
co
ld
ev
it
an
s
ie
es
pr
su
nt
sh
co
pla
nt
tr
n
ar
d
pa
nio
co
m
re
se
vit
so
ilg
u
ta
ns
ol
hie
ld
su
p
pla
nts
co
n
ntr
ro
vr
al
co
ol
0
0
bla
nk
Tu
sa
Tr
l
ic
ho
de
x
So
ilg
ar
C
om
d
pa
nio
Su
n
pr
es
ev
it
60
R
ov
ra
l
C
on
ta
ns
nt
sh
ie
ld
R
oo
ts
hie
ld
80
vr
al
„
record incidence of lettuce drop
record number and weight of marketable
lettuce heads
Yuma S. minor trial 2002
120
ro
„
Yuma Biocontrol Trials
Yuma S. sclerotiorum trial 2002
Healthy heads/50' bed
Evaluate the efficacy of
commercially available biocontrol
agents for the control of lettuce drop
B
la
nk
C
on
tr
ol
Sporidesmium sclerotivorum
he althy heads/ 50' bed
„
nk
„
bla
„
co
n
Trichoderma harzianum
Companion – Bacillus subtilis
RCBD with 4 blocks
biocontrol treatments plus one
fungicide treatment plus control
two trials - high and low density of
sclerotiasclerotia- S. minor and S. sclerotiorum
two application schedules - prepre-plant
application and prepre-plant plus side
application
healthy heads/50' bed
„
„
la
nk
on
tr
ol
R
ov
ra
l
C
on
Pla tan
s
nt
sh
ie
R
ld
oo
ts
hi
el
d
Tu
sa
Tr
l
ic
ho
de
x
So
i lg
ar
C
om
d
pa
Su nio
n
pr
es
ev
it
„
„
B
„
Contans - Coniothyrium minitans
Soilgard - Gliocladium virens
Trichodex,
Trichodex, Supresivit,
Supresivit, TRI 002 -
C
„
Evaluate the efficacy of
commercially available biocontrol
agents for the control of lettuce drop
healthy heads/ 50' bed
Evaluate the efficacy of
commercially available biocontrol
agents for the control of lettuce drop
Blank
Untreated control
Rovral
Contans
Imperial Valley Biocontrol Trials
Holtville S. minor trial 2003
120
healthy heads/50' bed
140
120
100
80
60
40
20
100
80
60
40
20
n
pa
ni
o
co
m
ta
ns
co
n
an
ts
hi
el
d
pl
tr
ol
ro
vr
al
co
n
bl
n
co
m
pa
nio
ta
ns
co
n
pla
nt
sh
ie
ld
tr
ol
ro
vr
al
co
n
an
k
0
0
bl
an
k
healthy heads/50' bed
Holtville S. sclerotiorum trial 2003
140
4
Blank
Untreated control
LongLong-term Objective
To develop biocontrol strategies for
desert winter lettuce production that
are compatible with chemical and
cultural management strategies
Rovral
Contans
5