•
DIAMONDBACKMOTH CONTROL
•
THE
VEGETABLE
FARMER •
MARCH 2017
today, but we need to get away
from the idea that DBM is a
sporadic pest in the UK.”
The importance of
diamondback moth as a pest was
emphasised by Dr Rosemary
Collier of Warwick Crop Centre,
who gave an overview of the
pest’s biology and research to
date. The fact that when eggs
first hatch, the very small larvae
burrow into the foliage, and the
rapid life cycle, where the
caterpillar feeding stage can be
completed in just 20 days under
typical summer weather
conditions, and the fact that the
caterpillars are green, means that
spotting the pest and controlling
it in a timely manner is a
challenge. “Last year vast
numbers of moths arrived,” she
pointed out. “They were also
seen in Scandinavia. Themoths
came to the UK in several waves,
but over a fairly short period.”
Meteorologist Charlotte
Wainwright, from Rothamsted
Research described her work
usingweather data and
information onmoth populations
across Europe to track migration
patterns. “The week of 24thMay
saw the first population increases
in the UK, and the big push into
the UK came on 1st June 2016,”
she explained.
“By comparing themoths’
movement withweather patterns
we are able to trace them
backwards and see where they
aremigrating from.” By tracing
the first arrivals, whichwere
found in light traps up and down
the east coast, Charlotte
concluded that these first waves
last year came fromNorway.
“Although there were big
populations in Holland and
Belgium, the winds didn’t
support DBMmovement to the
UK from here during the first big
arrival.”
Charlotte explained that due to
their relatively small size, DBM
aremore dependent on being
carried on the wind than other
species, such as Silver Ymoth. “If
weather patterns had been
different, we could have had a
big influx from Benelux. Because
themoths are so small, they
don’t havemuch speed and
direction of their own,” she
explained. With this modelling of
historic migrations, it should be
possible to give some prediction
about future arrivals, even
though this will depend on being
able to identify moths on the
continent.
Most delegates felt that even
24 hours warningwould be
useful, giving them notice to
watch out for the pest’s arrival.
“We needmore data to find the
locations which provide the best
overwintering sites for
populations,” she added. “Our
model can only improve as we
get data from other countries.”
Being able to predict the arrival
of diamondback mothmore
accurately would be a big step
forward, but growers still need to
be able to control pest
infestations when they occur. Dr
Steve Foster of Rothamsted
explained the testing of DBM
samples that took place in 2016,
which showed strong resistance
to pyrethroids inmany
populations. “Themessage is
don’t use pyrethroids,” he
stressed. Not only will they not
control DBM due to resistance
issues, but they will also reduce
many potential beneficial insects
whichmay otherwise help to
control the population level.
Testing showed no resistance to
diamides or spinosad, but with
restrictions on the total use of
diamides, growers and
agronomists need to be careful in
their choice of products. “We
know that resistance to diamides
does exist elsewhere (in Asia), so
we would need to check that,”
said Dr Foster. “There is also
resistance to Bt and spinosad
(Tracer) in other parts of the
world. We have relatively few
modes of action remaining and
we need to be aware of the risk
of creating and selecting for
home-grown resistance.”
The general feeling among
attendees at the workshopwas
that without access to the new
chemistry of Cyazypyr® in
Verimark, crop damage would
have beenmuchworse, but
Andrew Rutherford and others
pointed out that becoming over-
reliant on a single product could
increase the likelihood of
resistance to that particular active
or mode of action. During
12
Dr Rosemary Collier of Warwick Crop
Centre.
Diamondbackmoth larva and damage [pic courtesy Rosemary Collier].
Dr Steve Foster of Rothamsted
Research.
