Thresholds (Pest and disease assessment)

  • If the threshold for a pest or disease is reached appropriate action should be taken.
  • The thresholds given here are simple (i.e. they do not take into account variety or crop or other factors).
  • They are generally conservative to ensure a margin of safety.
  • If a pest or disease is just below the threshold, repeat sampling after a short period may be appropriate.

Sampling methods, treatment thresholds and actions and their timings if thresholds are exceeded for apple pests and diseases in Integrated Pest and Disease Management

Time/growth stage

Sampling unit per tree (visual inspection unless beating specified)

Pest/disease threshold

Threshold

Action and time for treatment
Dormant period
2 vegetative buds on one-year shoots Apple rust mite Average 10 mites per bud Treat with a suitable selective acaricide at mouse-ear
4 branch nodes on 2-3 year old wood Fruit tree red spider mite winter eggs 30% branch nodes with >5 eggs Treat with clofentezine (Apollo) before flowering, preferably before mouse-ear
Whole tree

Wood scab

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Apple mildew (silvered shoots) ] ]
Apple canker and wood-rotting fungi ] Presence Remove during winter pruning
Mummified brown rot fruit ] Remove or push into alleyway to be macerated by mower
Whole orchard Over-wintering leaf litter Easily found Macerate to encourage breakdown prior to bud-burst
Bud-burst to mouse ear
Beat 2 branches (if pest present previous year) Apple blossom weevil adults 5 weevils per 50 beats Treat with chlorpyrifos (Dursban etc.) as soon as possible
2 outer rosette leaves Apple rust mite Average of 5 mites per outer leaf Treat as soon as possible pre-blossom
Green cluster to pink bud
Whole orchard Rosy leaf curling aphid Presence on rosette leaves Spot treat with aphicide
Whole tree Apple scab % trees infected:
<5% = low

5-20% = moderate

>20% = high

 Intensify programme of eradicant and protectant fungicide sprays at full dose, reduce spray interval according to severity and risk of infection
Beat 2 branches Apple blossom weevil adults 5 weevils per 50 beats Treat with chlorpyrifos (Dursban etc.) as soon as possible
4 blossom trusses Rosy apple aphid 1 infested per 25 trees ]
Apple grass aphid 30% trusses infested ]
Apple sucker 30% trusses infested ] Treat with suitable insecticide at
Winter moth or tortrix  moth caterpillars 2% trusses infested ] Late green cluster to pink bud
Primary apple mildew 2% mildewed blossoms ]Intensify programme of eradicant and protectant fungicide sprays at full dose and medium volume (500 l/ha), reduce spray interval
Early blossom
Whole orchard Blossom wilt Presence previous year Apply suitable fungicide at early blossom and repeat 10 days later
Late blossom to 80% petal fall
Whole orchard Apple sawfly 1 or more adults caught in white sticky trap or pest present  at threatening levels previous year Treat with suitable insecticide within 7 days of petal fall
Whole tree Apple scab Presence of visible symptoms Intensify programme of eradicant and protectant fungicide sprays at full dose, reduce spray interval
Primary vegetative mildew 2% mildewed shoots Intensify programme of eradicant and protectant fungicide sprays at full dose and medium volume (500 l/ha) reduce spray interval.
European apple canker, Neonectria fruit rot >25% with canker Indicates high risk of fruit infection and need to apply sprays at petal fall and 14 days later to protect fruit
Rosy apple aphid 1 infested per 25 trees Treat with suitable insecticide at petal fall
Capped blossoms caused by apple blossom weevil Presence Earmark for treatment with thiacloprid (Calypso) at bud burst the following year
4 trusses Apple sawfly 10 egg insertions per 100 trusses Treat with suitable insecticide within 7 days of petal fall
Winter moth or clouded drab moth caterpillars 3 caterpillars per 100 trusses Treat with suitable insecticide at petal fall
Capsid 2 trusses per 100 trusses infested or damaged Treat with suitable insecticide promptly at petal fall
Receptacles of 2 flowers per tree Apple rust mite on receptacle or calyx An average of 1 or more mites per flower or fruitlet Treat with suitable acaricide promptly at petal fall
Mid-May
10 trusses on each of 4 branches Scab on leaves, flowers or fruitlets % trusses infected:
<2.5% = low

2.5-9.0% = moderate

>9% = high

 Intensify programme of eradicant and protectant fungicide sprays at full dose, reduce spray interval according to severity and risk of infection
2 leaves per tree Fruit tree red spider mite Average of 2 mites per leaf Treat with suitable acaricide promptly
Apple rust mite Average of 5 mites per leaf

(greater numbers of mites may be tolerated if the orchard predatory mite Typhlodromus pyri is abundant.  See sections on fruit tree red spider mite and apple rust mite)

 Treat with suitable acaricide promptly
Fortnightly after petal fall (June, July, August and, where necessary, September)
Whole tree Rosy apple aphid 1-2 colonies Treat with suitable aphicide as soon as possible
Woolly aphid 4% of trees with aphids on extension growth Treat with suitable aphicide as soon as possible
Rosy leaf curling aphid Presence Spot treat with suitable aphicide
Sawfly Presence Earmark for treatment following year
Blossom wilt Presence Prune out. Treat with fungicide following year
Canker in 1-2 year old shoots Presence Prune out. Treat with fungicide at leaf fall
Neonectria eye rot Presence A moderate to high incidence indicating risk of rotting in store
4 shoots per treeScab on leaves Scab on leaves % shoots infected:
<2.5% = low

2.5-9.0% = moderate

>9% = high

 Intensify programme of eradicant and protectant fungicide sprays at full dose, reduce spray interval according to severity and risk of infection
Top (apical) 5 leaves in 2 growing shoots per tree Secondary apple powdery mildew 8% of leaves mildewed = 30% shoots infected Intensify programme of fungicide sprays at full dose and medium volume (500l/ha), reduce spray interval
2 leaves per tree Fruit tree red spider mite Average of 2 mites per leaf Treat with suitable acaricide as soon as possible
Apple rust mite Average of 10-50 mites per leaf, higher value later in season

(greater numbers of mites may be tolerated if the orchard predatory mite Typhlodromus pyri  is abundant.  See sections on fruit tree red spider mite and apple rust mite)
Fruit on whole tree Sooty blotch and fly speck Presence Earmark for treatment next year. Implement cultural control measures
Pheromone traps Codling moth >5 moths per trap per week for 2 weeks, not necessarily successive.
Applications of granulovirus may need to be made slightly before this threshold is reached.		 Treat 7-10 days after threshold catch (exact interval calculated from max and min daily temperature)
Fruit tree tortrix moth >30 moths per trap per week Treat about 2 weeks after threshold catch
Summer fruit tortrix moth 30 moths per trap per week
or significant damage previous year		 Treat 7-10 days after threshold catch (exact interval calculated from max and min daily temperature).
Shortly before harvest (14-7 days before harvest)
Whole orchard Storage rots Conduct rot risk assessment  
Brown rot Assess incidence on fruit: > 1% indicates high risk of rot in store Selective picking at harvest
Phytophthora rot Assess incidence of bare ground in tree row (20% or more = risk) and % of crop less than 0.5 m from ground (15% or more = risk) 20 mm or more rain in 15 days before harvest in orchards at risk = risk of rot in store. Options: avoid harvesting low fruit for store or market early.
Post harvest in orchard
Whole orchard Canker Damaging levels present (25% of trees or more) Apply copper sprays at leaf fall – check status of current authorisation
10-20 leaves per tree Late scab infection on undersides of leaves Present
< 3% scabbed = low

>3% scabbed = high

 Spray urea shortly before leaf fall and macerate fallen leaves in winter

Place at least one trap for each species (codling, fruit tree tortrix and where it occurs, summer fruit tortrix moth) in each major block of fruit.