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CATERPILLAR PESTS OF BRASSICA CROPS – 21st May 2019
Summaries of sightings of diamond-back moth and silver Y moth in several northern European countries in 2019 can be found here: https://warwick.ac.uk/fac/sci/lifesci/wcc/research/pests/plutella/sightings2019/. These are moths captured or seen and reported on 'biodiversity monitoring' websites.
The summaries of ‘citizen science’ moth sightings in the UK and on the continent will be supplemented by on- farm monitoring of diamond-back moth by several members of the Brassica Growers Association.
Large numbers of diamond-back moths arrived in the UK on Friday 17th May https://warwick.ac.uk/fac/sci/lifesci/wcc/research/pests/plutella/sightings2019/. The moths were first seen along the east coast of England but may have moved since then. This seems to have been the only ‘pulse’ of moths so far as lower numbers have been seen since then.
If they arrive in brassicas then it is likely that the female diamond-back moths will lay eggs quite rapidly. You can get some idea of how long the eggs might take to hatch from the table on this web page https://warwick.ac.uk/fac/sci/lifesci/wcc/research/pests/plutella/.
On-farm monitoring of diamond-back moth by members of the Brassica Growers Association and others
Date Location Number of moths Number of traps 30 April Lancashire 1 2 7 May Lancashire 15 6 14 May Cornwall 1 2 14 May Lancashire 7 6 17 May Wellesbourne 1 2 20 May Scotland Moths seen in crops - 21 May Lancashire 11 6
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Citizen Science – sightings of diamond-back moth and silver Y moth
Sightings of diamond-back moth and silver Y moth reported on websites since mid-April 2019 are summarised below.
3000 Diamond-back moth
2500
2000 Finland Norway 1500 Sweden Netherlands Belgium
Number of moths seen moths of Number 1000 UK Twitter UK Atropos
500
0
In partnership with
30 Silver Y moth
25
20 Finland Norway 15 Sweden Netherlands Belgium
Number of moths seen moths of Number 10 UK Twitter UK Atropos
5
0
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Numbers of butterflies and moths captured at Wellesbourne in 2019.
Date Diamond-back Cabbage moth Silver Y moth Turnip moth (2 Small Large moth (2 (2 pheromone (2 pheromone pheromone white white pheromone traps) traps traps) butterfly butterfly traps) (6 water (6 water traps) traps) 14 May 0 0 0 4 1 0 17 May 1 0 0 1 0 0 20 May 0 0 0 0 0 0
In partnership with
2018
Sightings of diamond-back moth and silver Y moth reported on websites in 2018 are summarised below.
1800 Diamond-back moth
1600
1400
1200 Finland Norway 1000 Sweden Netherlands 800 Belgium
UK Atropos Number of moths seen per day perseen moths of Number 600 UK Twitter
400
200
0 01-Apr 01-May 01-Jun 01-Jul 01-Aug 01-Sep 01-Oct
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3500 Silver Y moth
3000
2500
Finland 2000 Norway Sweden Netherlands 1500 Belgium
UK Atropos Number of moths seen per day perseen moths of Number UK Twitter 1000
500
0 01-Apr 01-May 01-Jun 01-Jul 01-Aug 01-Sep 01-Oct
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Moth and butterfly captures at Wellesbourne 2018
Date Diamond-back Silver Y moth Cabbage moth Small white Large white moth (2 traps) (2 traps) (2 traps) butterfly (3 butterfly (3 traps) traps) 3 July 9 0 0 0 0 6 July 6 1 0 3 0 10 July 11 2 0 0 1 13 July 6 5 0 0 0 17 July 7 15 0 0 0 19 July 3 4 0 0 0 24 July 0 5 0 0 0 27 July 0 4 0 0 1 31 July 3 2 0 0 0 3 August 1 0 0 0 0 7 August 2 0 0 0 0 10 August 0 0 0 1 0 14 August 1 0 0 0 0 17 August 1 2 0 0 0 21 August 0 0 0 1 0 24 August 0 0 0 2 0 28 August 0 1 0 1 0 31 August 0 0 0 1 0 4 September 0 2 0 0 0 7 September 0 0 0 0 0 11 September 0 4 0 0 0 14 September 0 1 0 0 0 18 September 0 0 0 0 0 21 September 0 0 0 0 0 25 September 0 0 0 0 0 28 September 0 0 0 0 0 2 October 0 0 0 0 0 9 October 0 0 0 0 0 16 October 0 1 0 0 0 23 October 0 2 0 0 0 30 October 0 0 0 0 0
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Background
The caterpillars of a number of species of moth and butterfly can be pests of brassica crops:
Species Activity periods Importance
Small white butterfly May/June and late summer – more Can be damaging and hard to see on (Pieris rapae) abundant in late summer plants
Large white butterfly May/June and late summer – more Can be damaging but usually attacks a (Pieris brassicae) abundant in late summer small number of plants and damage is generally obvious
Cabbage moth May/June and late summer – more Localised pest – can be hard to see on (Mamestra brassicae) abundant in late summer plants when young
Garden pebble moth May/June and late summer – more Localised pest – hard to see on plants (Evergestis forficalis) abundant in late summer
Diamond-back moth Migrant and can arrive at any time – Can be very damaging and hard to see on (Plutella xylostella) usually from June onwards plants when small
Silver Y moth Migrant and can arrive at any time Rarely causes significant damage on (Autographa gamma) from early spring brassicas
Turnip moth Late May-early July, sometimes a Rarely causes significant damage on (cutworm) (Agrotis second generation in later summer – brassicas segetum) forecast available