The timing and management of the harvest is a compromise. Early harvesting usually means lower harvesting rates, losses due to harvesting of immature cherry, and incomplete removal of ripe cherry from the tree. As the harvest is delayed, the cherry matures and becomes easier to harvest. Delaying the harvest therefore increases harvesting rates but also increases losses due to a higher proportion of lower quality overmature and tree-dried cherry being harvested, and the associated high risk of total loss of this cherry falling to the ground.
Smaller growers are restricted in their harvesting options by the availability of a harvester and processing equipment suitable for machine-harvested cherry. Some growers may hand-harvest a proportion of the crop early in the season before a single pass of the harvester later in the season if they cater for the higher priced gourmet market. More recently small, low cost hand-held pneumatic harvesters have become available.
The limited availability and high cost of labour dictate that harvesting must be fully mechanised in large scale operations in Australia. Due to the time taken to achieve one harvester pass over the entire crop, the harvest strategy chosen must aim to maximise total recovered yield.
Results of harvesting trials, coupled with the experience of commercial operators, has led to the development of guidelines for maximising the recovery from machine-harvesting.
- Determine when the maturity peak should occur, based on the timing of peak flowering (seven to eight months from flowering in North Queensland; nine to ten months in northern New South Wales).
- Tag one or more representative laterals in the top, middle and bottom section of each of about 20 randomly chosen trees. Regularly assess the maturity of cherry on these laterals.
This information is then assessed against the following standards:
- Immature cherry has little or no value, and can be considered as the lowest value product. High levels (>20%) of immature cherry in any sample mean significant losses. High levels of immature cherry also increase the probability of contamination of prime cherry in all but the most sophisticated processing systems.
- Overmature cherry has some value, but is prone to falling from the tree, particularly if wet by rain or overhead irrigation during the latter stages of maturity.
- For ease of harvest, prime cherry should be fully ripe (purple if possible) (see below, stages six to eight).
- If conditions are cool and dry, and undertree irrigation is used, cherry life will be many weeks. If conditions are warm and humid, cherry life will be reduced.
- Remember that cherry life is shorter for cherry exposed at the top of the tree than for cherry shaded in the middle or bottom section of the tree.
- The top third of the tree usually carries 20% to 30% of the cherry. The middle third of the tree carries 40% to 50% of the cherryand the bottom third the remaining 20% to 40%.
In machine-harvested plantations, the first crop of cherry is unlikely to be harvestable because of the low yield, poor accessibility by the harvester to cherry on lower laterals, and the potential for tree damage. It is usually commercially viable to harvest the second crop, particularly if the harvester can harvest laterals to within 400 mm of the ground.
The following techniques will help fine-tune harvest management for young trees:
- Delay the harvest until most of the crop has reached either mature (full red) or preferably very mature (purple) (see Table above). This ensures easy removal and limits damage to young trees. It is not normally advisable to harvest young trees if more than 20% the cherry on the tree accessible to the harvester is immature. flowering synchronisation has been poor, delay the harvest; it will have little effect on prime cherry recovery, and will ensure more complete removal of all cherry from the tree.
- If, due to extreme variability in maturity, and after consideration the above recommendations, more than one harvester pass is necessary, ensure that both passes are very gentle, and that the trees are good health and well-watered.
Once trees are fully mature (five years), strategies for maximising recovered yield of prime cherry become important. Climate, cultivar type, tree health and degree of flowering synchronisation affect cherry maturity patterns which develop on the tree. There are three main ripening patterns:
- The top is significantly more mature than the lower sections of the tree
- A wide range of cherry maturities exist throughout the tree
- An even ripening pattern exists throughout the tree
Identifying the ripening pattern allows the development of a harvesting strategy to maximise recovery.
Significant ripening pattern
Providing a reasonable degree of flowering synchronisation has been achieved, a significant ripening pattern is normally established, although variability in cherry maturity will still exist. In this case, a two or three pass selective layer harvest is suggested. As explained earlier, the timing and severity of each pass depends on the proportion of immature cherry in the zone to be harvested.
No significant ripening pattern
This is the worst harvesting scenario, usually resulting from poor flowering synchronisation and weather conditions which do not favour a long cherry life. The rate at which cherry becomes harvestable must be compared with losses due to cherry becoming overmature and falling. A two or three pass selective harvesting regime is probably the most appropriate regime to adopt. The first pass should not be attempted until less than 50% of the total cherry on the tree is immature, and a very selective harvesting pass should be used (low speed, low shaker frequency). Although the cherry in the top section of the tree is highly visible, it usually represents less than 25% of the total cherry on the tree. For this reason, data from the tagged laterals should be used to assess correct harvest time. After the first pass there will he some acceleration of ripening. If cool and dry weather conditions are likely to extend cherry life, further delaying of the harvester passes is desirable.
Very even ripening
This will only exist where there has been a high degree of flowering synchronisation, where the trees are still young, where the tree structure has been modified by pruning, or where shade from adjacent rows has affected tree structure. If conditions are conducive to extended cherry life, it is best to delay harvesting until most cherry is very mature and harvest in a single pass.