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Winter moth (Operophtera brumata (L.))

Winter moth larva

Winter moth caterpillar feeding cavities in fruitlet

Winter moth damage to truss

Corky scars on fruit at harvest

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.

Control  

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.

  • Diflubenzuron (Dimilin), indoxacarb (Steward) and methoxyfenozide are selective materials which are likely to control caterpillars only and have little effect on aphids.
  • Indoxacarb (Steward) may give some control of capsids. Spinosad (Tracer) may also be effective.
  • Fenoxycarb (Insegar) is not a good choice because it only controls caterpillars in their later stages of development and will not prevent early damage to buds, blossoms and fruitlets.
  • 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 intervalbetweensprays(days)
Bacillus thuringiensis Dipel bacterialinsecticide selective to caterpillars c (SOLA) safe 7
deltamethrin Decis pyrethroid broad spectrum cm, t harmful none stipulated
diflubenzuron Dimilin CSI selective c, cm, ftt safe none stipulated
indoxacarb Steward oxadiazine selective c, cm, ftt, sft u 10
methoxyfenozide Runner MAC selective c safe u
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 zoneWidth (m)
Anticholin-esterase?  Humans Fish & aquatic life Bees
Bacillus thuringiensis no u u u 0 u u
deltamethrin no h, i ed d 7 u 50
diflubenzuron no u u u 14 2 20
indoxacarb no h ed u 7 3 15
methoxyfenozide no u u u 14 3 5
spinosad no u ed u 7 4 40
Keys:     1CSI=chitin synthesis inhibitor2c=caterpillars, cm=codling moth, ftt=fruit tree tortrix, sft=summer fruit tortrix,  t=tortrix

3d=dangerous, ed=extremely dangerous, h=harmful, i=irritant,  t=toxic, u=no hazard specified

 

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) 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.

 

Further reading