Winter moth is an important pest of apple and pear. The life cycle involves wingless females crawling up the tree trunk to lay eggs in the bark.
The green caterpillars feed amongst the blossom trusses from green cluster to early June. They damage developing fruitlets by feeding on them. The cavities heal to form characteristic corky scars.
The pest is usually most abundant at the edges of orchards adjacent to woodland (especially oak) and hedgerows.
Although superficially similar to some other caterpillar pests they can be distinguished by having only two pairs of prolegs.
Populations of larvae should be monitored by visually inspecting trusses at green cluster to pink bud before bloom. If more than 5% of trusses are infested, a pre-blossom insecticide application is justified.
A wide range of insecticides are approved for control of caterpillar pests on apple and all these are likely to control winter moth, which is sensitive to insecticides. In the past, some growers traditionally applied a pre-blossom spray of a broad-spectrum insecticide such as chlorpyrifos (no longer approved on apple) to control aphids and caterpillars including those of the winter moth. But many other insecticides when applied before blossom will also control winter moth and have varying degrees of activity against different pests.
- Indoxacarb (Steward or Explicit) is a selective material which is likely to control caterpillars only and have little effect on aphids.
- Spinosad (Tracer) may also be effective.
- Pyriproxyfen (Harpun) is approved for use on apples for codling moth control but may offer incidental control of winter moth. It inhibits egg hatch, metamorphosis of nymphs to adults and reduces the fecundity of adult females. However, as a new product to the UK in 2020, further experience is required to inform growers and agronomists of its efficacy at controlling winter moth.
- Synthetic pyrethroids are also highly effective against winter moth but their use should be avoided because they are harmful to important orchard natural enemies including the orchard predatory mite.
Insecticides approved on apple for control of winter moth, codling moth, tortrix moths or caterpillars or offer incidental control when applied to control other pests
| Choice of insecticides – efficacy factors | ||||||
|---|---|---|---|---|---|---|
| Active ingredient | Trade name (examples) | Class1 | Selectivity | Label rec’s2 | Safety to Typhs | Suggested interval between sprays (days) |
| Bacillus thuringiensis var. kurstaki | Dipel DF | bacterial insecticide | selective to caterpillars | c (SOLA) | safe | 7 |
| deltamethrin | Decis Forte etc. | pyrethroid | broad spectrum | c, cm, t | harmful | none stipulated |
| indoxacarb | Steward, Explicit | oxadiazine | selective | c, cm, ftt, sft, wm | u | Varies with product |
| pyriproxyfen | Harpun | metamorphosis inhibitor | selective | cm | safe | none stipulated |
| spinosad | Tracer | neural blocker | selective | C, cm, ftt,sft | safe | u |
| Choice of insecticides – Safety factor Read and and follow the label before applying any sprays |
|||||||
|---|---|---|---|---|---|---|---|
| Hazards2 | Harvest interval (days) | Max. no. sprays | Buffer zone width (m) | ||||
| Anticholin-esterase? | Humans | Fish & aquatic life | Bees | ||||
| Bacillus thuringiensis | no | u | u | u | Varies with product | Varies with product | 5 |
| deltamethrin | no | h, i | ed | d | 7 | u | 50 |
| indoxacarb | no | h | ed | u | 7 | 3 | 15 |
| pyriproxyfen | no | d | t | u | fruit diameter up to 40mm | 2 | 20 |
| spinosad | no | u | ed | h | 7 | 4 | 40 |
| Keys: 1CSI=chitin synthesis inhibitor2c=caterpillars, cm=codling moth, ftt=fruit tree tortrix, sft=summer fruit tortrix, t=tortrix, wm=winter moth 3d=dangerous, ed=extremely dangerous, h=harmful, i=irritant, t=toxic, u=no hazard specified |
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Control in organic orchards
Winter moth is often one of the most damaging pests in organic orchards.
- In organic orchards it should be controlled using cultural control methods (see ‘Cultural control’).
- Spinosad (Tracer) and Bacillus thuringiensis(Dipel DP) are the only materials approved for organic orchards.
- Bacillus thuringiensis can be fairly effective providing temperatures are warm at and shortly after application so that caterpillars are feeding actively.