The influence of cabbage stem flea beetle (Psylliodes chrysocephala (L.)) on yields of oilseed rape


Purvis, G.

1986 British Crop Protection Conference Pests and diseases Volume 2 Proceedings of a conference held at Brighton Metropole, England, November 17-20, 1986: 753-759

1986


Damage assessment trials to investigate the effects of cabbage stem flea beetle (Psylliodes chrysocephala) on yields of winter oilseed rape are described. Results indicate that if an application of an effective insecticide is made in NovemberDecember when larval numbers are five per plant or greater, a yield response of 0.34 tonnes per ha (at 92% dry matter) can be expected and use of this population level in late autumn as a treatment threshold will avoid significant yield losses. Preliminary results also indicate that no extra yield increment is obtained from spring treatment if effective autumn control measures have been taken, even if subsequently larval numbers increase to over 13 per plant by April. In the absence of autumn control, springapplied treatment appears to give a worthwhile yield response if larval numbers in spring increase to at least five per plant or more. The possibility that incidental control of aphid vectors of beet western yellows virus can affect yield response to cabbage stem flea beetle treatments is also discussed.

1986
BRITISH
CROP
PROTECTION
CONFERENCE—PESTS
AND
DISEASES
7
A
5
THE
INFLUENCE
OF
CABBAGE
STEM
FLEA
BEETLE
(Psylliodes
chrysocephala
(L.))
ON
YIELDS
OF
OILSEED
RAPE
G.
PURVIS
ADAS,
Harpenden
Laboratory,
Harpenden,
Herts.
AL5
2BD,
UK
ABSTRACT
Damage
assessment
trials
to
investigate
the
effects
of
cabbage
stem
flea
beetle
(Psylliodes
chrysocephala)
on
yields
of
winter
oilseed
rape
are
described.
Results
indicate
that
if
an
application
of
an
effective
insecticide
is
made
in
November-December
when
larval
numbers
are
five
per
plant
or
greater,
a
yield
response
of
0.34
tonnes
per
ha
(at
92%
dry
matter)
can
be
expected
and
use
of
this
population
level
in
late
autumn
as
a
treatment
threshold
will
avoid
significant
yield
losses.
Preliminary
results
also
indicate
that
no
extra
yield
increment
is
obtained
from
spring
treatment
if
effective
autumn
control
measures
have
been
taken,
even
if
subsequently
larval
numbers
increase
to
over
13
per
plant
by
April.
In
the
absence
of
autumn
control,
spring-applied
treatment
appears
to
give
a
worthwhile
yield
response
if
larval
numbers
in
spring
increase
to
at
least
five
per
plant
or
more.
The
possibility
that
incidental
control
of
aphid
vectors
of
beet
western
yellows
virus
can
affect
yield
response
to
cabbage
stem
flea
beetle
treatments
is
also
discussed.
INTRODUCTION
During
the
expansion
of
winter
oilseed
rape
production
in
England
and
Wales
since
the
mid-1970s
(Anon.1985),
cabbage
stem
flea
beetle
(CSFB)
Psylliodes
chrysocephala
(L.)
(Coleoptera:
Chrysomelidae)
has
become
a
widespread
and
damaging
pest
(Alford
&
Gould
1975,
John
&
Holliday
1984).
Early
work
showed
that
chemical
control
of
CSFB
on
overwintering
brassica
crops
could
be
achieved
using
gamma-HCH
(Williams
&
Carden
1961)
and
subsequently
more
effective
organophosphorus,
carbamate
and
pyrethroid
insecticides
were
identified
(Alford
1977,
John
&
Holliday
1984).
Experience
of
CSFB
attacks
in
the
Agricultural
Development
and
Advisory
Service
(ADAS),
has
led
to
the
general
adoption
of
a
treatment
threshold
for
advisory
purposes
of
five
larvae
or
more
per
plant
in
autumn.
In
the
present
paper,
data
from
trials
done
by
ADAS
are
used
to
test
the
general
validity
of
this
threshold
and
more
recent
work
on
the
pest
potential
of
late-hatched
larvae
entering
plants
in
spring
is
reported.
METHODS
Autumn
threshold
trials
The
validity
of
the
currently
used
autumn
damage
threshold
for
CSFB
was
investigated
in
six
trials
done
in
Hertfordshire
and
Cambridgeshire
between
1982/83
and
1984/85.
In
each
trial,
yields
following
the
application
of
carbofuran
granules
at
the
rate
of
1.25
kg
a.i.
per
ha
immediately
after
sowing
(before
crop
emergence)
were
compared
with
753
7A-5
untreated
controls
in
a
randomized
block
design
with
either
four
or
five
replications.
Plots measured
100
m
2
(usually
4
x
25
or
5
x
20
m)
and
yields
were
determined
by
harvesting
strips
of
either
2.23
or
3.66
m
width
from
entire
plot
lengths.
Results
were
expressed
in
tonnes
per
ha
at
92%
dry
matter
(d.m.).
Larval
CSFB
numbers
were
determined
by
dissection
of
20
randomly
selected
plants
per
plot
in
late
November/early
December
and
again
in
February/March.
Spring
threshold
trials
In
three
modified
trials
done
in
the
1984/85
season,
the
effect
on
yield
of
spring-hatched
larvae
was
investigated
using
the
following
treatments:
i
HCH
-
a
single
application
of
gamma-HCH
at
560
g
a.i.
per
ha
in
early
November,
likely
to
give
adequate
autumn
protection
only;
ii
HCH+Ph
-
a
single
application
of
gamma-HCH
as
above
followed
by
the
application
of
phorate
granules
at
200
g
a.i.
per
ha
in
February,
to
give
full
autumn
and
spring
protection;
iii
Ph
-
phorate
alone
applied
as
above
in
February;
iv
U
-
untreated
control.
Each
treatment
was
replicated
four
times
in
randomized
blocks
and
larval
numbers
were
assessed
as
before
in
untreated
plants
in
December,
January,
March
and
April
to
determine
initial
population
levels
and
the
subsequent
extent
of
spring
hatching.
Populations
on
insecticide-treated
plots
were
assessed
in
January
and
April
only.
Yields
were
determined
as
previously
described.
RESULTS
Autumn
threshold
trials
Untreated
larval
populations
varied
considerably
between
autumn
trial
sites
and
years
(Table
1)
and
ranged
from
0.57
to
6.67
larvae
per
plant
at
assessments
made
in
late
November/early
December.
No
notable
increases
in
untreated
populations
were
detected
in
February/March
and
carbofuran
treatment
was
seen
to
give
effective
control
(P<0.05-0.01)
at
both
assessments
in
all
trials
(Table
1).
Significant
yield
responses
to
carbofuran
treatment
(P<0.05)
were
obtained
only
in
the
trials
with
five
or
more
larvae
per
plant
on
untreated
plots
in
December
although
in
all
trials,
the
carbofuran
treatment
gave
a
higher
mean
yield
than
the
control
(Table
1).
Figure
1
shows
yield
responses
obtained
in
a
series
of
similar
damage
assessment
trials
done
by
ADAS
in
recent
years
using
a
range
of
organophosphorus,
carbamate
and
pyrethroid
insecticides
applied
in
autumn.
Only
data
from
treatments
achieving
at
least
70%
reduction
of
larval
populations
in
late
autumn
were
included
in
this
analysis
and
754
7A-5
trials
in
which
substantial
spring
hatching
subsequently
occurred
were
excluded.
A
significant
(P<0.001)
regression
of
yield
response
on
untreated
larval
numbers
indicated
an
expected
yield
loss
of
0.34
tonnes
per
ha
(@
2%
d.m.)
at
the
currently
advocated
autumn
threshold
of
five
larvae
per
plant.
At
this
threshold,
the
95%
confidence
limits
for
the
yield
response
obtained
in
a
single
trial
range
from
0.01
to
0.67
tonnes
per
ha.
Table
1
Summary
of
larval
populations
and
yield
responses
obtained
in
autumn
damage
threshold
trials
comparing
immediate
post-sowing
treatment
with
carbofuran
(T)
and
untreated
controls
(U),
1982-1985
Year
of
trial
(no.
of
replicates)
Treatment
Mean
larvae
per
plant
Nov.-Dec.
Feb.-Mar.
Yield
(tonnes
per
ha
@
92%
d.m.)
1982/83-I
T
0.3**
0.8**
2.19*
(4)
U
5.8
5.4
1.56
1983/84-I
T
0.3
0.5*
4.09
(4)
U
0.6
2.5
4.06
1983/84-11
T
0.4*
0.8*
2.39
(4)
U
2.0
2.1
2.08
1984/85-I
T
0.5*
1.0**
3.59*
(
5
)
U
5.0
7.3
3.38
1984/85-11
T
0.5*
1.0*
2.76*
(
5
)
U
6.7
6.5
2.17
1984/85-111
T
1.0**
1.9*
2.71
(
5
)
U
3.9
4.1
2.50
*
and
**
indicate
significant
difference
from
control
mean
(U)
at
P<0.05
and
0.01
respectively.
Spring
threshold
trials
The
results
of
larval
assessments
made
in
spring
threshold
trials
are
shown
in
Tables
2-4.
In
trial
I,
autumn
larval
numbers
reached
the
threshold
of
five
per
plant
but
subsequent
spring
hatching
increased
this
population
to
7.5
larvae
per
plant
in
April.
All
combinations
of
autumn
and
spring
treatments
significantly
reduced
populations
at
appropriate
times.
Although
no
significant
yield
responses
were
obtained
in
this
trial,
mean
yields
on
autumn
treated
plots
were
substantially
greater
than
on
untreated
controls
but
the
yield
difference
between
autumn
treatment
alone
and
combined
autumn
and
spring
treatment
was
relatively
small
(Table
2).
755
8
0
0
0
0
0
O
0
O
O
y
=
0.044
+
0.060X
0
0
0
0
0
0
lower
95%
confidence
limit
0
0
0
•••
7A-5
Yield
increase
cf.
mean
untreated
yield
(tonnes
per
ha
@
92%
d.m.)
1.2
Upper
95%
confidence
limit
for
the
1.0
yield
response
of
a
single
treatment
2
4
6
8
10
12
Untreated
mean
number
of
larvae
per
plant
(Dec/Jan)
Fig.
1
Relationship
between
mean
larval
numbers
per
plant
on
untreated
plots
in
December/January
and
yield
response
under
treatments
achieving
at
least
70
per
cent
reduction
of
CSFB
populations;
regression
line
and
95
per
cent
confidence
limits
for
the
yield
response
expected
of
a
single
treatment.
'O
0.8
0.6
0.4
0.2
0.0
756
7A-5
Table
2
Summary
of
larval
populations
and
yield
responses
obtained
in
spring
threshold
trials
in
1984/85
comparing
combinations
of
autumn
control
using
HCH
(HCH)
and
spring
application
of
phorate
(Ph)
with
an
untreated
control
(U);
trial
I
(four
replications
per
treatment)
Treatment
Mean
larvae
per
plant
Yield
(tonnes
per
ha
@
92%
d.m.)
December
January
March
April
HCH
NA
2.1*
NA
1.7***
4.00
HCH+Ph
NA
0.6**
NA
0.3***
3.77
Ph
NA
4.9
NA
1.1***
3.57
U
5.0
5.9
7.3
7.5
3.37
S.E.D.
(9
d.f.)
-
1.58
-
0.77
0.20
*,
**
and
***
indicate
significant
difference
from
control
(U)
mean
at
P<0.05,
0.01
and
0.001
respectively;
NA
=
not
assessed.
In
trial
II,
larval
numbers
exceeded
the
autumn
threshold
and
were
greater
than
six
per
plant
in
December.
A
substantial
spring
hatch
increased
numbers
to
over
13
larvae
per
plant
by
April.
HCH
effectively
controlled
the
autumn
larval
attack
but
failed
to
control
the
subsequent
spring
invasion.
Larval
numbers
were
effectively
reduced
by
the
phorate
application.
All
treatments
gave
significant
yield
responses
compared
with
the
untreated
control,
but
relatively
little
additional
response
accompanied
spring
phorate
treatment
following
an
autumn
application
of
HCH
(Table
3).
Table
3
Summary
of larval
populations
and
yield
responses
obtained
in
spring
threshold
trials
in
1984/85;
trial
II
(details
as
Table
2)
Treatment
Mean
larval
numbers
per
plant
Yield
(tonnes
per
ha
@
92%
d.m.)
December
January
March
April
HCH
NA
2.5**
NA
13.8
2.61**
HCH+Ph
NA
3.0*
NA
2.3**
2.63**
Ph
NA
9.7
NA
4.3**
2.28*
U
6.67
9.2
6.5
13.5
1.85
S.E.D.
(9
d.f.)
-
1.67
-
2.61
0.23
757
7A-5
In
a
third
trial,
autumn
numbers
were
below
four
larvae
per
plant
but
subsequent
hatching
increased
this
population
to
almost
seven
per
plant
by
April.
All
treatments
gave
good
control
and
produced
signficant
yield
responses
but
no
additional
yield
increment
was
obtained
from
the
phorate
treatment
following
an
autumn
application
of
HCH.(Table
4).
Table
4
Summary
of
larval
populations
and
yield
responses
obtained
in
spring
threshold
trials,
in
1984/85;
trial
III
(details
as
Table
2)
Treatment
Mean
larval
numbers
per
plant
Yield
(tonnes
per
ha
@
92%
d.m.)
December
January
March
April
HCH
NA
1.2***
NA
3.6**
2.91**
HCH+Ph
NA
1.1***
NA
0.5***
3.05***
Ph
NA
3.89
NA
0.9***
2.73*
U
3.8
4.7
4.1
6.8
2.54
S.E.D.
(9
d.f.)
-
0.73
0.71
0.07
DISCUSSION
Analysis
of
data
available
from
damage
assessment
trials
on
CSFB
confirms
the
general
validity
of
the
currently
used
autumn
treatment
threshold
of
five
or
more
larvae
per
plant
in
November/December
and
shows
that
by
acting
upon
this
threshold,
signficant
yield
losses
will
normally
be
avoided.
Preliminary
data
on
the
significance
of
spring
populations
enhanced
by
late
hatching
indicate
that,
in
the
absence
of
previous
autumn
treatment,
an
effective
spring
treatment
will
give
a
worthwhile
yield
response
if
larval
numbers
in
February-March
exceed
five
per
plant.
However,
if
autumn
control
has
already
been
achieved
subsequent
spring
hatching
at
the
levels
recorded
does
not
appear
to
warrant
the
use
of
further
control
measures.
This
probably
reflects
the
greater
damage
potential
of
larger
instars
derived
from
autumn
hatching
and
the
relatively
greater
susceptability
of
plants
to
mining
damage
prior
to
the
resumption
of
rapid
growth
in
spring.
In
consequence,
effective
autumn
treatments
which
prevent
mining
by
large
overwintered
larvae
before
the
resumption
of
spring
growth
appear
to
produce
the
greatest
yield
benefit.
Early
ADAS
experience
of
trials
work
on
CSFB
using
the
then
standard
and
comparatively
non-aphicidal
treatment
gamma-HCH,
frequently
failed
to
show
signficant
yield
responses
at
autumn
larval
population
levels
of
at
least
five
per
plant
(D.V.
Alford,
personal
communication).
Evidence
presented
here,
however,
shows
clearly
that
using
materials
of
wider
and
improved
insecticidal
activity,
significant
yield
responses
are
readily
obtainable
at
this
population
level.
In
view
of
this
anomaly,
recent
758
7A-5
evidence
of
the
widespread
occurrence
of
Best
Western
Yellows
Virus
in
winter
oilseed
rape
in
the
UK
(Smith
&
Hincks
1985)
is
particularly
suggestive;
at
least
some
of
the
yield
response
obtained
in
CSFB
damage-
assessment
trials
using
current
insecticides
may
be
attributable
to
the
incidental
control
of
the
aphid
vectors
of
BWYV.
As
yet,
little
is
known
about
the
epidemiology
of
this
virus
in
OSR
or
about
its
effect
on
yield.
Further
ADAS
trials
on
CSFB
have
therefore
been
modified
to
include
a
specifically
aphicidal
treatment
which
will
not
affect
CSFB
and
BWYV
infection
is
being
measured
on
all
treatments.
In
this
way,
it
is
hoped
to
quantify
any
virus
component
in
yield
responses
to
CSFB
treatments
which
may
then
enable
further
revision
of
the
treatment
threshold
for
CSFB
in
those
areas
where
virus
is
not
present.
ACKNOWLEDGEMENTS
The
author
is
indebted
to
colleagues
in
ADAS
who
made
the
results
of
their
trials
work
available
for
regression
analysis
and
especially
to
Dr
D.V.
Alford
and
H.J.
Gould
for
their
comments
on
the
manuscript.
REFERENCES
Alford,
D.V.
(1977)
Chemical
control
of
the
cabbage
stem
flea
beetle,
Psylliodes
chrysocephala,
on
winter
oilseed
rape.
Annals
of
Applied
Biology
85
(3),
369-374.
Alford,
D.V.;
Gould,
H.J.
(1975)
Surveys
of
pest
incidence
on
oilseed
rape
in
the
U.K.
Proceedings
8th
British
Insecticide
and
Fungicide
Conference
2,
489-495.
Anon.(1985)
Annual
Review
of
Agriculture
1985.
H.M.S.O.,
London,
50
pp
John,
M.E.;
Holliday,
J.M.
(1984)
Distribution
and
chemical
control
of
Psylliodes
chrysocephala
and
Ceutorhynchus
picitarsis
in
winter
oilseed
rape.
Aspects
of
Applied
Biology
6,
281-292.
Smith,
Helen
G.;
Hinckes,
Jennifer
A.
(1985)
Studies
on
beet
western
yellows
virus
in
oilseed
rape
(Brassica
napus
ssp.
oleifera)
and
sugar
beet
(Beta
vulgaris).
Annals
of
Applied
Biology
107
(3),
473-484.
Williams,
J.J.W.;
Carden,
P.W.
(1961)
Cabbage
stem
flea
beetle
in
East
Anglia.
Plant
Pathology
10,
85-95.
759