Pre-blossom visual assessment
- Inspect at least 100 trusses (e.g. 4 on each of 25 trees) per orchard for signs of damage or infestation by winter moth larvae at the green cluster to pink bud growth stage of apple.
- Inspect trees at the edge of the orchard adjacent to woodland or hedgerows where the risk of infestation is high, as well as those in the centre and other parts of the orchard where the risk of infestation is lower.
- If damage is seen, open up truss to see if a winter moth larva is present.
- A hand lens should be used to distinguish small caterpillars of the winter moth (2 pairs of prolegs) from those of tortrix or noctuid (e.g. clouded drab) moths (5 pairs of prolegs).
- Treatment with an insecticide is justified if 5% or more of trusses are infested.
Late blossom visual assessment
- The same methods are used as for the pre-blossom visual assessment.
- However, the treatment threshold is 3% of trusses infested, lower than the pre-blossom threshold.
Late blossom assessment using the beating method
- Beat at least 20 branches per orchard over a beating tray.
- The treatment threshold is 1 caterpillar or more per 20 beats.
Damage at harvest
- The percentage of fruits with corky scars, characteristic of early caterpillar feeding, should be monitored at harvest and during grading.
- If the percentage exceeds 0.1%, this is an indication that control methods that season were not optimal and more effective measures are likely to be needed the following year.
Pheromone traps for adults
- The female-produced sex pheromone of winter moth has been identified and lures containing synthetic pheromone can be acquired from specialist manufacturers and suppliers.
- Pheromone traps placed in orchards from October to January often catch large numbers of males but these may be attracted over considerable distances from woodland and hedgerows and may have little significance in terms of populations in the orchard. For this reason they are not used commercially.
Grease banding of trunks
- A band of a recommended grease may be pasted round the lower trunk of a sample of trees in September to October to monitor the number of ascending females in winter.
- Note that grease bands may be phytotoxic to young trees.