Gloeosporium and Colletotrichum rots are difficult to monitor in the orchard, since the rots are rarely seen, the cankers not easily distinguishable from those caused by Nectria and the fungi not readily distinguishable on other inoculum sources such as weeds.
- An estimate of the incidence of Gloeosporium and Colletotrichum rots in the orchard can be obtained by examination of about 100 rotted fruit from the rot bin, when the fruit from that orchard is graded and identifying the rots present.
- Disease forecasting systems have not been developed.
- During the six years in which rot risk assessment was developed, the incidence of Gloeosporium rot in the Cox orchards used in the study was very low and sporadic.
- Consequently it was difficult to get any clear correlations between Gloeosporium incidence and other factors.
The following criteria are suggestions based on the limited data available.
Assessment of the risk of rotting in store
The assessment for rots due to Gloeosporium and Colletotrichum spp. On Cox is based on:
- Orchard rot history (from packhouse records).
- Crop load – light crops with larger fruit size are more prone to Gloeosporium and Colletotrichum rots because of lower calcium levels.
- Rainfall in the month prior to harvest. Above average rainfall increases risk of Gloeosporium and Colletotrichum rots.
- Fruit mineral composition – low calcium high potassium levels giving a K/Ca ratio of >30.
- While on Cox fruit with low calcium levels are more prone to Gloeosporium rotting, the rot may occasionally occur at high incidence in store on fruit of good mineral composition.
- Reasons for the occurrence of Gloeosporium rots in these instances are not clear but must be assumed to be associated with high inoculum in the orchard and favourable weather prior to harvest.
The rot may occasionally occur at high incidence in store on Gala, a variety which is usually of high calcium content and does not merit pre-harvest calcium sprays.
- Reasons for the occurrence of Gloeosporium rots in these instances are not clear but must be assumed to be associated with high inoculum in the orchard and favourable weather prior to harvest.
- Gloeosporium and Colletotrichum rots often occur in orchards with a high incidence of Nectria canker.
Decisions on Gloeosporium and Colletotrichum rot risk
- Cox apples of low calcium status and where K/Ca ratio is >30 should not be stored long term.
- For Cox apples suitable for long-term storage but with a history of Gloeosporium and Colletotrichum rots, monitor the rainfall in the month prior to harvest.
- Where rainfall is >than average then schedule fruit for marketing before January if fungicide sprays have not been applied.
- At present the incidence of Gloeosporium and Colletotrichum rots in Gala and Bramley is low (except where fruit has deteriorated prematurely due to a physiological disorder) and does not merit special action.