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Sooty Blotch (Gloeodes pomigena) and Fly Speck (Schizothyrium pomi)

 

Sooty blotch and flyspeck on apple fruit

Sooty blotch and fly speck are two distinct diseases of apple but usually occur together. The diseases occur sporadically in conventionally sprayed orchards but are prevalent and can cause serious losses in wet seasons in organic orchards or where fungicide use is reduced.

The fungi cause characteristic symptoms of a sooty-like discolouration (sooty blotch) or black shiny dot blemishes (fly speck) on near mature fruit and, although superficial, this causes fruit to be downgraded and reduced in value.

 

The life cycle and epidemiology of these fungi involves overwintering on apple twigs and on many hedgerow and wild tree species.  In spring spores produced on apple twigs and hedgerow hosts spread in wind and rain to infect apple twigs and subsequently infect fruit from early summer to harvest. The diseases are favoured by cool moist conditions.

Control

At present control is dependent on an integrated approach combining monitoring,  and cultural measures with fungicide use.

  • Trim hedgerows to limit inoculum.
  • Prune apple trees to ensure good light penetration and air circulation so that fruit dries rapidly.
  • Maintain good weed control to ensure good air circulation.
  • Where the disease has been a problem the previous season, apply sprays of an effective fungicide to fruit in early summer (mid-late June) and in July and August.
  • Mancozeb (Karamate) is the most effective fungicide.
  • DMI fungicides such as myclobutanil (Systhane) are ineffective and captan has only limited effectiveness.

Fungicides approved for use on apple which offer some incidental control of sooty blotch when applied to control other diseases – efficacy

Active ingredient Trade name Fungicide group Typh safety Efficacy
boscalid + pyraclostrobin Bellis strobylurin (QoI) safe effective ?
captan Captan 80 WDG

PP Captan 80

phthalimide safe partial
kresoxim-methyl Stroby WG strobylurin (QoI) safe effective ?
mancozeb Karamate Dry FloPenncozeb WDG dithiocarbamate harmful effective

Fungicides approved for use on apple which offer some incidental control of sooty blotch when applied to control other diseases – safety factors

  Hazards     Buffer zone
Active ingredient human fish + aquatic life bees Harvest interval (days)  Max. no. of sprays Width (m)
boscalid + pyraclostrobin h d u 7 4 30
captan h, ir, c t u 31 10 30 
kresoxim-methyl h t u 35 4 sm
mancozeb ir t u 28 4 40 

d = dangerous; h = harmful; ir = irritating, a = may cause allergic reaction, t = toxic

PH = post harvest; Pre bb = pre-bud burst, sm=statutory minimum of 5 m for broadcast air assisted sprayers

u=uncategorised/unclassified/unspecified, c=closed cab required for air assisted sprayers

Control in organic orchards

  • Control is dependent on cultural measures.
  • Sulphur sprays appear to have only limited efficacy against the diseases. Potassium bicarbonate may also give some control.