Pre-harvest orchard performance appraisalResearch & Extension
By John Wilton
Just before harvest is a great time to assess the performance of your orchard management strategy, so there is time to start implementing changes to optimise next season’s crop.
I consider that just prior to harvest commencing is a key time to view the orchard and its crop. It is at this stage when any weakness in crop husbandry becomes most obvious so it is a good time to formulate future management policies.
Key things to look for are:
- Canopy density
- Crop uniformity
- Tree size variability
- Tree support weakness
Key things to do are:
- Firm up harvest strategies
- Prioritise block maturity monitoring
- Check fruit size ranges
- Identify where fine tuning of crop husbandry practices are necessary
- Check the state of orchard access tracks
Top dollar returns require perfect fruit
Fruit growing financial success and long term viability requires the production of high margin products. Buyers and consumers want a crisp, tasty fruit that meets a consistent quality standard. You need repeat sales to survive so your buyers and their customers need confidence that each time they purchase your product it will give a similar level of satisfaction as the last consignment.
Product consistency is the aim, and this requires a uniform orchard canopy that has been well thinned, then harvested at optimum maturity and given best practice post-harvest treatment.
Top quality fruit requires an open canopy that allows good light penetration down into the fruiting zones. Fruit taste and colour is very dependent on the fruit having been grown in a good light environment. Calm, low vigour branches are needed to produce this light environment.
Identify any areas in the orchard where there is too much vigour leading to excessive shading of fruiting zones. In later varieties where the harvest period is four to five weeks away there is still time to open up the canopy with a bit of judicious summer pruning or even a leaf plucking if variety value is sufficient to justify the expense.
Summer pruning to let more light in needs to be very carefully supervised to avoid taking out too much leading to sunburn problems, or reducing next season’s crop potential by taking next year’s fruiting wood.
I generally view this type of summer pruning as a temporary solution to the problem. The long term solution is to be able to recognise the characteristics of the branches that are causing the problem and taking them out before next season.
Uniform crop loads are critical for maximising both yield and fruit quality. It will also tell you whether or not there are biennial bearing problems. However, in my experience, irregular hand thinning is the main cause of variable crop loads.
Variable crop loads are often linked to tree vigour variation. Vigorous trees readily shed fruit while weak growing trees hold onto their crop. Chemical thinners are generally less effective on low vigour trees and it’s mighty difficult to get the hand thinners to take enough fruit off the weaker trees.
Provided the initial thinning pass has been reasonably good with fruit singled, or in no more than twos, pre-harvest re-thinning is possible without running a high sunburn risk. Re-thinning at this time can be done by fruit size and this means that only trees with excess crop will be thinned.
In New Zealand, pre-harvest touch up thinning for our premium high value crops is generally considered necessary in order to maximise Class 1 packout, as well as spread some of the harvest labour requirement to a less busy time. Often there is a process market outlet for these thinnings, which helps defray some of the re-thin cost.
Where high fruit colour is required it is necessary to have fruit in singles to avoid the within bunch fruit to fruit shading problem.
Bunchy crops are extremely difficult to manage for both uniform fruit quality and harvest. Where you are caught with a bunchy crop now, it is necessary to take out whole bunches, or live with it and hope that the packing line can sort the mess out, which they will be willing to do at a price that may not leave you much margin.
It is also a good time to check pollination. If there is a fall off in crop density with increasing distance from pollinator trees then there are not enough of them.
Tree size variability
Uniform tree size is the key to high orchard performance.
Areas of weak-growing or excessively vigorous trees need to be mapped, and then the reasons for the divergence from the average tree size investigated.
Weak growing areas are usually related to a problem with root health, water stress or poor drainage. Often it’s an area in the orchard where there is shallow top soil due to soil levelling at some time in the past. Further down the row there will be some very vigorous trees growing where the lost top soil now resides.
Strategies to encourage weak trees to grow are much more difficult than taking the vigour out of high vigour trees. The best tools we have to make them grow include:
- Improving drainage
- Mulching to conserve moisture
- Reducing flower bud numbers during pruning
- Removal of any choking branches during pruning
- Giving good upper tree leader support
- GA3 sprays to stimulate growth
Compared with making stubborn trees grow, calming down excess vigour is relatively easy. The tools we have include:
- Minimal pruning regimes
- Selective removal of high vigour branches
- RDI (reduced deficit irrigation)
- Root pruning
- Trunk girdling
- Growth regulators, e.g. Regalis®, Ethephon
Once you start pushing up orchard performance, tree support becomes more critical. Each year we see a few rows fall over due to insufficient tree support.
The pre-harvest period is a critical time to check tree support structures are performing as they should. Crop weight is beginning to rise rapidly at this time so structure weakness is easily spotted.
In intensive plantings be wary of any trees that are leaning off the row centre. Where central leader trees are vertical their trunk takes most of the crop weight, but once they get a lean on it is the support structure that takes the weight.
Check tree ties, trellis attachment to support structures, and appraise if there are sufficient posts in the trellis to do the job.
Where support structure problems are found an effort should be made to address the problem immediately. This may involve aggressive upper tree thinning to re-balance the crop weight, use of tree props to give added support for the trees, or checking and replacing tree ties and staples.
As part of this programme, gathering data on block maturity and fruit size range is necessary in order to make rational decisions. Maturity monitoring should begin three to four weeks prior to the anticipated harvest date.
Checking fruit size six or eight weeks before harvest will give a good indication of the fruit size range at harvest. There is now good data on fruit sizing curves available on OrchardNet® which can be used to forecast harvest size.
Tracking fruit size data will also indicate if the trees can handle the crop load. Where crops are too heavy, growth rates stall. If your fruit sizing rate falls behind others in your district, this would indicate that re-thinning to take off smaller sized fruit will be well worthwhile.
Having good fruit sizing data will also indicate if it’s necessary to apply Retain® to hold maturity back. As a general rule, fruit size increases by about 1 per cent a day through the harvest period. Delay your harvest by 10 days and you will have a 10 per cent increase in both yield and fruit size.
For red and partially coloured varieties, laying down reflective mulch between the rows three or four weeks before harvest can make a huge difference to fruit colour. This increases crop value markedly, speeds up harvest, and enables the crop to be harvested at a more optimum maturity due to improved fruit colour.
Stop drop sprays
Pre-harvest drop can be quite a problem in some varieties. We do not see it much in Royal Gala types, but varieties such as Red Delicious and particularly Scifresh and Braeburn, fruit drop can be quite severe.
NAA applied sequentially from about three weeks pre-harvest at 5ppm has been found to be very effective for reducing the drop problem. Retain® also gives good control of pre-harvest drop.
Handling damage, such as bruising and stem punctures can be a major quality problem. Although the pickers get saddled with much of the blame, it’s my opinion that their role in the problem is minor compared to the injury that poor orchard tracks and rough forklift drivers can cause. Orchard tracks need to be in good condition at harvest to minimise fruit injury.
We have also noticed over the years that fruit maturity at harvest has a profound influence on handling damage. Fruit harvested early in the harvest period always fares much better than that harvested at advanced maturity.
APAL’s Future Orchards® program is funded by Horticulture Innovation Australia Ltd using the apple and pear industry levy funds from growers and funds from the Australian Government. AgFirst is a key Future Orchards partner.
About the author
John Wilton was a Horticultural Consultant at AgFirst, New Zealand.