Post-harvest decay relates to decay developing after the fruit have been harvested or during the handling and storage phase. Although decay development occurs after harvest, the process may manifest prior to harvest, while only emerging during storage. Losses during the post-harvest phase can be rapid and severe.
Various fungal pathogens may cause post-harvest decay on apricots. Severe losses may be encountered, ranging from direct monetary, to indirect loss in market share, where confidence is lost in a product range delivered from an area or fruit from a specific producer.
Causes / rot types:
Apricots may exhibit several post-harvest rot types, caused by fungal pathogens, of which brown rot (Monilinia laxa), grey mould rot (Botrytis cinerea) and rhizopus rot (Rhizopus stolonifer) is most important, occurring in all the production regions of South Africa. Other decay types, such as penicillium rot, mucor rot and alternaria rot may also cause post-harvest losses. The intensity of decay and the causal pathogen may vary annually per area, cultivar and also orchard. Weather conditions, but also fruit physiology and handling conditions may affect the infection process and progress of the decay type.
Fruit can be infected in the presence of fungal matter, if conditions are favourable. The fruit (referred to as the ‘host’) and the environment are the other two components of the disease triangle, which dictates the establishment and progression of infection. The infection process in the case of the fungi most prevalent on apricots relies on the presence of spores (also referred to as conidia) on the fruit, followed by attachment, germination and colonisation of the host tissue. Disease expression may follow if conditions are favourable for further development. Blossoms and mature fruit are by far most susceptible.
Spores and other fungal matter present in the orchard, are referred to as ‘inoculum’. However omni present, the inoculum load may vary during the season. Availability of susceptible hosts and prevailing weather condition, affect the inoculum load. It is important to continuously strive to reduce the available inoculum load, which is mainly infected fruit of the present season, but also the previous season (referred to as ‘mummies”), to lower the risk of infections.
The decay types generally infect fruit more readily the more advanced the maturity, but other structures such blossoms, leaves and twigs, and also immature fruit, may be infected, remaining latent or quiescent (invisible) until factors holding the development back are negated.
Pre-harvest weather conditions may impact on fruit physiology and directly or indirectly on pathogen development. Rain or dew with a wetting period of 10 hours or more and high humidity (>80%), as well as mild ambient temperatures (15 – 25 °C), are favoured by all the pathogens. As a general rule, fruit should be dry before harvest.
Injuries are often the origin of decay development, providing the point of entry for the fungal spores, as part of the infection process. Injuries in the form of abrasions, punctures and bruises, also those caused by the short, stocky spurs of some apricot cultivars, predispose the fruit to infections. Insect damage also provides place of entry for fungal spores and should be minimised.
Decay levels tend to increase the longer the storage and the higher the storage temperature, which enhance fruit ripening and senescence. Low temperatures of ± 0 °C during storage will slow down respiration and fruit deterioration, but also decay progression. Most of the fungi referred to will not be totally controlled by these conditions, but infection will be slowed down. High humidity, or the presence of free water, such as from condensation, promotes germination of fungal spores. This leads to infection or growth of previously established infections with consequential decay development.
Sanitation entails the removal and destroying of any plant material that has become infected, therefore, eradicating, eliminating or supressing the source for future infections.
Diagnosis of which disease or pathogen is involved is necessary to take preventative or corrective actions.
Careful handling and avoidance of injuries
To handle, pack and store apricots with low post-harvest decay risk, it is necessary to reduce the possibility of infections establishing in the orchard. Injuries play a major part in the infection of apricots.
Sanitation practices are essential for the reduction of decay on apricots. Sanitation entails the regular removal of all infected plant material from the orchard. The primary objective is to reduce the infection potential in the orchard prior to harvest, as well as later in the handling chain. All fruit on the orchard floor should be removed and disposed of outside the orchard. After harvest, all remaining fruit and mummies (old and desiccated decayed fruit|) must be removed from the trees.
The use of fungicides or biological products is essential for the control of post-harvest decay. Orchard applications should preferably start at the blossom phase, but continue until prior to harvest. The use of post-harvest fungicides can further assist decay control. For application of chemicals during the pre-harvest phase, refer to guidelines on available registered products as supplied by ‘Agri-Intel’. Refer to their website for an updated list of fungicides acceptable for use on plums to various market segments. All fungicides must be used as per direction on the label.
Fungicide resistance may occur for some chemical groups applied pre-harvest. Repetitive or sustained fungicide treatments of one chemical group or cross-resistance between groups, may increase the risk of resistance. Botrytis and Penicillium spp. are generally regarded as pathogens showing a high risk for the development of resistance to fungicides, while Monilinia is regarded as a medium risk pathogen. For the latest information on resistance or cross resistance status to other chemical groups, contact your local crop protection advisor or product manufacturer representative.
Post-harvest fungicides permissable for use on apricot (and other stone fruit).
Removal of all infected material which could be of potential inoculum source. This is applicable for all places where the fruit is handled during and after harvest. Fruit showing visible signs of decay and/or injury should be removed before reaching the pack-house. Picking units, whether large bins, smaller crates or bags, should be clean and free from soil and plant debri.
Harvesting & packing:
Fruit should be harvested and packed with care, avoiding injuries. Injuries can be in the form of punctures, bruising or skin breaks. Detection of injuries at time of harvest already indicates a high decay risk. Special care should be given to apricot cultivars with strong, short spurs, as tissue tears may occur when harvesting. If fruit need to be harvested a few of days after problematic weather conditions have abated (e.g. rain / prolonged wetting), fruit that are slightly less mature or still of optimum maturity (rather than overripe) have a lower risk of decay development. An orchard inspection is advised after adverse weather conditions, to ascertain which orchard / cultivar is most suitable for harvest, with the objective of providing low decay potential fruit to the pack-house, for subsequent storage.
Apricots should be kept under cold storage conditions, preferably as close to 0 °C possible, for the shortest duration. Decay on apricots caused by all the pathogens listed increases as the storage duration increases.
Only use post-harvest fungicides as listed in the table. The time between harvest and application of fungicides should be minimised, since chemicals become less effective the longer the delay. The efficacy of post-harvest fungicides does not only depend on the dosage, but also on efficacy of deposition and adherence to the fruit surface. Residue limits, referred to as MRL (maximum residue limit) need to be adhered to at all times (refer to the Agri-Intel website for further information; access to this information is by registration).