Processors and Growers Research Organisation
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PGRO Crop Update Number 2: 21st May 2024

PGRO Crop Update: CB2402
Silver Y moth
There have been reports of high numbers of Silver Y moths across the country. The caterpillar of the Silver Y moth feeds on foliage and pods and can cause a degree of defoliation when infestation levels are high. Given the high numbers reported this year, foliar damage is a possibility. The main problem occurs when the caterpillar becomes a contaminant in vined peas, or when feeding damage to pods of fresh market peas or beans makes them unmarketable. Adult moths are about 10 – 15 mm in length, have a brownish grey hairy body and greyish coloured wings, with a distinctive silver coloured y marking on each forewing. They can fly during the day or night and may be seen actively flying in crops on warm days. They can often be found flying from plant to plant within the main foliage and at rest, often are seen with the wings folded back and rapidly ‘shivering’.
Most moths migrate to the UK from Mediterranean countries or North Africa. The moths feed on nectar and lay eggs singly or in pairs on the foliage. The eggs are white, round, flattened and about 0.5 mm in diameter. After 10 – 14 days, the eggs hatch and caterpillars begin feeding on the leaves. At first, the damage appears as small discrete craters on the leaf surface, but as the caterpillars grow over the following two weeks, the damage becomes more extensive to both leaves and pods.
Caterpillars are bright green in colour varying in size up to 20 - 25 mm in length. There is a light-coloured thin stripe along the sides of the caterpillars, and they possess only two pairs of abdominal ‘pro-legs’ which allows them to move with a looping action.
Silver Y moth migration is sporadic and because of this, populations vary between years, and it is difficult to predict numbers in any one season. Order silver Y moth traps to be placed in fields as soon as possible. Traps are available from the following suppliers:
Dragonfli, Unit 4 Rippers Court, Sible Hedingham, Halstead, Essex, CO9 3PY, UK
Tel: 01376 563322
Andermatt UK, 47 Compton Road, Brighton, West Sussex, BN1 5AL, UK
Tel: 07939 395059
 In peas, the trap is placed at crop height in the field in mid-May and moths, caught in the base, are counted on three occasions during each week of monitoring. A threshold is reached when a cumulative total of 50 moths has been reached by the time that the peas have reached the first pod stage (BBCH 67).
When the threshold has been reached, a single spray of a pyrethroid insecticide, approved for pea moth control, should be applied 10 - 14 days later. This application will control both large and small caterpillars, which fall off the plants before the crop is harvested. The same trap can be used in green beans or runner beans for monitoring populations although a threshold for treatment has not been formulated. However, where significant numbers of moths are caught regularly, crops should be inspected for caterpillars 7 - 14 days after first recording moths, and a spray applied where caterpillars can be found on crops which are about 7 days from harvesting.

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