Gloeosporium and Colletotrichum can be important causes of rotting in stored Cox and other varieties and both have increased in incidence in recent years causing significant losses. They rarely occur as rots in the orchard.
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| Gloeosporium fruit rot | Gloeosporium fruit rot | Colletotrichum spp. on Bramley |
The rots are caused by three species of fungi, mainly G. album and G. perennans and Colletotrichum spp. (formerly G. Fructigenum).
Symptoms caused by the three fungal species on fruit are similar and symptoms are similar on all cultivars.
The fungus usually enters the fruit via a lenticel producing a cheek rot, but it may also occur around the stalk or calyx where it enters via a wound or small crack.
The rot is mid-brown (possibly darker on Egremont Russet), circular, moderately firm and frequently, but not always, forms concentric zones of different colours as the tissue is invaded.
Lesions usually have yellow centres on Cox, progressing to dark brown at the interface between healthy and infected tissue. On Egremont Russet the rots are often uniform brown.
Cream-coloured slimy pustules may be produced during storage on rots caused by Gloeosporium spp. Pink / orange slimey pustules may be present on rots caused by Colletotrichum spp., particularly after they have been in the rot bin for a day or two.
The life cycles and epidemiology are similar for all three fungi. They all over-winter in the orchard as cankers (G. perennans), on dead twigs, leaves or on mummified fruit (G. album and Colletotrichum spp.)
Spores produced on these in wet weather during the growing season infect fruit from blossom to harvest. Infection remains latent and subsequently develops in store usually after December.
The risk of rotting in store can be determined pre-harvest based on rot history from packhouse records and the rainfall in the month pre-harvest (>average = risk).
For Cox, fruit mineral composition (low calcium – status fruit, K/Ca ratio >30) is also important in determining risk.
Control
- Control is based on an integrated approach combining cultural measures of inoculum removal in the orchard with chemical control where a risk has been identified.
- Only fruit of the correct mineral composition should be stored long-term.
- Orchards with a history of Gloeosporium or Colletotrichum rot should be sprayed pre-harvest with sprays of captan, Switch (cyprodinil + fludioxonil) or Bellis (pyraclostrobin + boscalid) in July and August.
Organic production
Control of Gloeosporium and Colletotrichum rot in organic orchards is dependent on cultural measures in the orchard, ensuring fruit for storage is of correct mineral status and using rot risk assessment to determine risk in store.