Monitoring and control of the silver Y moth on field crops

Silver Y moth is a migratory species and does not overwinter in the UK. Larval feeding damages the foliage of several crops, particularly lettuce, and the presence of larvae or frass can cause contamination issues.

• Lettuce is one of the most susceptible crops
• Infestations may not be detected until after damage has occurred
• It is a migratory pest and crops in the south and east of England may be at greater risk. Large numbers of moths can arrive suddenly

Scientific name: Autographa gamma

Adults are grey to greyish-brown with a distinct silver Y mark on each forewing and a wingspan of 35–40 mm.

Eggs are oval (0.5–0.6 mm diameter) and white, darkening close to hatching.

Larvae are 24–40 mm long, green (ranging from bright green to very dark green) and have a dark green dorsal line edged with white. A light yellow line runs over the sides. The caterpillars ‘loop’ as they walk.

Oct–Mar: This species cannot survive the winter in the UK. It overwinters overseas.

Apr: Immigrant moths may arrive. Migration patterns vary widely from season to season.

May–Jun: Immigration risk period peak.

May–Jul: Eggs laid singly on susceptible host plants. Female moths lay an average of 150–650, eggs but can lay up to 1,500.

May–Jul: Larvae feed.

Jul–Aug: Mature larvae pupate on leaves within a loose web–like cocoon.

Aug–Sep: Moths migrate southwards.

It is estimated that 10–240 million immigrants reach the UK each spring and that summer breeding results in a fourfold increase in the abundance of the subsequent generation of adults, all of which emigrate southwards in the autumn.

Non-chemical control

Several polyphagous predators attack this pest. The larvae may also be parasitised by certain species of wasp or fly, which eventually kill the larvae. The larvae continue to feed for some time after they have been parasitised, so crop damage is not reduced immediately. Larvae may also be killed by viruses.

To date, biological control with predators or parasitoids has not been investigated in the UK. Pesticides based on microbial control agents (for example, Bacillus thuringiensis, Bt) may be effective.

Monitoring

Pheromone traps can trap moths in very high numbers. Light traps, run by moth enthusiasts, also catch moths. In Dorset, the first silver Y moths were captured on 26 April 2013 (a cold spring) and on 28 March 2012 (a warmer spring).

Thresholds

Vining peas: the threshold is reached when the cumulative catch (pheromone traps) exceeds 50 moths by the first pod stage (growth stage 204).

Sugar beet: the threshold is five caterpillars per plant.

Insecticide resistance

None known.