Pushing orchard performance boundariesResearch & Extension
AgFirst’s John Wilton hones in on some key factors – particularly chemical thinning in the lead up to spring – that orchardists can concentrate on to optimise yield and fruit colour.
In preparation for writing this article I spent some time trawling through our OrchardNet™ Australian database. The database shows that in general, Australian orchard yield performance is climbing.
The two major varieties in this database, Royal Gala types and Cripps Pink types, both show very healthy increases in per hectare yield performance over the period 2009/10 to 2015. Other varieties, excluding recently introduced cultivars such as Jazz™ and Kanzi™, have generally shown production increases too, but to a lesser extent.
It has also been reported, that with the increasing Australian crop, the market is coming under supply pressure leading to slimmer margins. This may tempt some producers to try and cut production costs to compensate for falling returns. For an intensive crop such as pome fruit this is a dead end road. Unless your production costs are well above industry norms do not try it. Focus on doing the best job you can to produce high quality fruit capable of maintaining or lifting unit profit margins.
Where working capital is likely to become limiting, the best solution to this problem is careful analysis of block and variety performance levels. Then, pull out the lower performers to make sure you have sufficient working capital, and irrigation capacity to maximise or maintain the yield and quality required to produce good margins on the better parts of the orchard.
One of the great myths in the pome fruit industry is that you have to be big to survive. Beyond the orchard gate there are huge economies of scale, but within it, once a production threshold is met, I doubt it.
The key to success within the orchard gate is careful focus and attention to detail with crop husbandry.
If you consider only harvesting costs to be the main variable on orchard expense, then the rest can be considered overheads. The only effective way to reduce overheads is to increase yields of high value, marketable crop.
Identify limiting factors
Scientists estimate that the genetic yield potential for apples is somewhere in the region of 175 to 200 t/ha based on efficient canopies capturing more than 70 per cent of solar energy falling on the planted area. This will vary a bit by variety, eg. large fruited cultivars have significantly higher yield potential than smaller fruited cultivars.
In Hawkes Bay (New Zealand), where we have ideal growing conditions in regard to summer temperatures, there are commercial plantings already doing around 150 t/ha on a sustainable basis.
In Australia, as in other continental production areas such as Chile, Argentina and South Africa, high summer temperatures are a limiting factor so I would not expect apples growing in very warm localities to comfortably achieve the scientists’ estimated yield potential. Even so, there are many Australian microclimates where excessively high summer temperatures do not occur that often. In these localities it should be possible to push orchard productivity well over the 100 t/ha level.
Present average production in Australia for Cripps Pink varieties is around 55 t/ha, and Royal Gala just over 40 t/ha. Top Cripps Pink yield blocks on our OrchardNet database are reaching 150 t/ha with the upper quartile average 92 t/ha. Similar figures for Royal Gala types are just over 100 t/ha with the upper quartile average 64 t/ha packing out 50 t/ha.
If you filter the Cripps Pink data by Class 1 per hectare, the higher yielding blocks drop down the table and the upper quartile Class 1 packed is 70 t/ha from a gross yield of about 91 t/ha. It is interesting to note that where yields were very high, Class 1 recovery was poor. These blocks have lower estimated profit levels than blocks producing only about two thirds of their gross yield, but high Class 1 packout.
Excess crop load becomes a major limiting factor when we consider maximising fruit quality. In addition, with many varieties excess crop load leads to biennial bearing problems.
Excess vigour is another major limiting factor to yield and quality. I note that Australian Fuji performance is low relative to other large fruited varieties. This is a variety that is very sensitive to excess vigour and also rather prone to biennial bearing if not managed well. Are Australian Fuji excessively vigorous and lacking sufficient fruiting sites because of the vigour problem?
Water stress and soil depth, fertility, structure and texture are major limiting factors to orchard performance in Australia. In recent years, high density orchards have become the norm, usually with drip or micro-sprinkler irrigation. As well as pushing yield boundaries, these newer intensive orchards have limited root volumes and consequently are only able to mine a small portion of the soil. Such plantings will be much more sensitive to nutrient and water stress than old, low performing standard plantings.
Is nitrogen a limiting factor?
Managing nitrogen levels in a partial red variety that you are trying to turn into a full red is very tricky. As harvest approaches you need to be aiming for nitrogen deficiency or close to it, then by flowering good nitrogen levels are necessary for fruit set.
Tree vigour is a poor guide to nitrogen status. Excess vigour is more likely to be associated with lack of crop, or inappropriate pruning rather than excessive nitrogen. Application of foliar nitrogen over the pre-bloom period is good insurance against poor fruit set.
We have also seen data supporting the view that low nitrogen status is implicated in biennial bearing as well as poor or irregular bud break. Our experience and observations lead us to believe that marginal nitrogen levels could be limiting fruit set and yield in many Australian orchard blocks.
Managing crop load
Careful attention to flower density and thinning is key to maximising orchard yield and fruit quality. The sooner the crop load can be brought down to optimum, the higher the recoverable Class 1 yield potential.
Where tree growth is poor and flower levels excessive, spur and flower bud thinning should be the first cut of the thinning programme. The actual process of flowering is very debilitating for the tree and in young plantings that are struggling to grow canopy volume, possibly does more harm than cropping. This is largely because by the time you get around to hand thinning the fruitlets have already done their damage to tree growth.
Markets are very demanding these days in regard to fruit colour. If your market requires better than 80 per cent full colour the crop has to be carried in singles, not bunches of two or more.
For high production in this situation you need a large, calm, open canopy with numerous well-spaced fruit buds and low vigour. Well settled canopies of this nature usually have strong blossom, which sets readily, and if crop loads have been well managed in the past do not have too much of a biennial bearing problem.
Such low vigour trees are often difficult to chemically thin. Because of high labour costs, limited labour availability and the short period with which to thin the crop, conventional orchard production has to rely on effective chemical thinning programmes.
Chemical thinning programmes
The Future Orchards® library on APAL’s website has many good papers on crop husbandry including chemical thinning.
Chemical thinning is as much an art as a science so it’s very difficult to write simple recipes for chemical thinning programmes. This is because so many factors, most outside of your direct control, affect the results.
Fear of over thinning is probably the most important limiting factor to successful chemical thinning results. Generally speaking, even with recognised aggressive programmes, instances of over thinning, entirely due to chemical thinning, are rare. Where over thinning occurs other compounding factors will also be present.
Likely factors leading to poor fruit set include:
- Soil water logging.
- Poor cross pollination, which is a big factor under nets.
- Excess vigour.
- High temperatures – caution with ethephon and benzyl adenine (BA).
- Frost – NAA more aggressive after a frost within 7 to 10 days prior to application which may have injured leaf leading to enhanced uptake. Ethephon can accentuate frost injury if frosts occur near time of application.
- Excessive shade – Carbaryl and BA thinners are more aggressive in shaded parts of the canopy.
- Re-wetting with rain – particularly ATS.
Major factors leading to chemical thinning failure include:
- Poor spray coverage.
- Unsuitable weather conditions for application, particularly low temperatures before, during and following application.
- pH of spraying water too high.
- Insufficient concentration of the thinner or its surfactant.
- Application under unsuitable conditions for spraying e.g. too much wind, or very low humidity leading to rapid drying blocking uptake.
- Extended blossom periods.
Sprayers need to be correctly calibrated for chemical thinner applications. This may be a different nozzle layout to that used for general pest and disease spraying
Upper tree fruit is often very difficult to thin well with chemicals, while lower tree fruit thins readily. This means larger nozzles may need to be directed at the upper tree than in general spraying, while nozzles directed at the lower and middle tree may need to be finer, or some even shut off all together.
Apart from blossom burner products such as ATS most chemical thinners are not all that phenologically stage sensitive. Correct weather conditions for application, therefore, overrides precise blossom or fruitlet development stage. Furthermore, under Australian climactic conditions the blossoming period can be stretched out, making it difficult to determine a precise development stage.
For thinners that are less sensitive to precise phenological stage, including NAA and BA, it’s better to think in terms of application windows and apply at the time that suitable conditions for them occur within that window.
The application window can also be broadened by using cocktails of several thinning products. For instance, the addition of ethephon to ATS enables a single spray to cover a range of flower stages, thus reducing the number of chemical thinning spray passes. This combination can be quite aggressive so I tend to use it later in the blossom, rather than early pre-blossom ethephon timing sometimes used in Australia. For this combination I am not game to recommend it until enough king bloom flowers are at petal fall stage to guarantee a crop.
NAA is a useful companion product to BA for those varieties not susceptible to setting pygmy fruitlets. Do not use on Fuji or Red Delicious. We now have good data to indicate that when NAA is added to BA the BA application window can be widened, possibly from average fruitlet size of 10 to 12mm diameter down to 7 to 8mm as a starting point.
In Europe there has been a lot of trial work with NAA plus BA on pears and this shows that the combination is much more aggressive than BA alone. I had a client here try it last year on a block of Beurre Bosc and a russet sport of Doyenne du Comice in their ‘on’ crop. This block had been thinned for a number of seasons with BA alone which for an ‘on’ year was nowhere near aggressive enough. The combination virtually eliminated the need for hand thinning.
There can also be quite large differences in chemical thinner effectiveness across a block depending on factors such as cross pollination pressure, tree vigour variation, and canopy light levels. Rows close to adjacent varieties, or along headlands where there is high tree traffic and high light levels usually set more fruitlets and are much more difficult to chemically thin. These ‘known’ hard-to-thin areas need a targeted, more aggressive chemical thinner approach.
Trees that received a good chemical thinning programme should look as if there is very little crop left three or four weeks later. If you can see lots of fruit, particularly in bunches at this stage, get ready for a big hand thinning job.
The key to pushing up the orchard performance boundary lies in setting optimum crop load levels within four to six weeks of bloom. Chemical thinning is a major part of achieving this goal.
Chemical thinning should never eliminate the need for hand thinning, but significantly reduce the required effort.
This problem continues to receive requests for further research and is well up the research priority list. Generally speaking, the warmer and more stressful the growing season, the bigger the biennial bearing problem.
Biennial bearing has received considerable research attention around the world and, by applying the solutions already developed from that research, it’s possible to bring it down to manageable levels.
Key tools for managing biennial bearing in pome fruit are:
- Low tree vigour.
- Large, calm canopies with adequate bud numbers to always have sufficient vacant bud sites for the following season’s crop.
- Setting crop loads within four to six weeks of full bloom.
- Appropriate use of growth regulators known to stimulate return bloom.
Grow quality fruit
High orchard financial performance depends on maximising the proportion of high quality fruit in the crop rather that maximising gross crop.
High fruit colour is king in the market place. Many markets are demanding 75 to 80 per cent or more fruit colour. Even with good red strains this means growing the crop in spaced singles.
Colour development is inhibited by shade, excess crop load and nutrient imbalance, particularly in regard to nitrogen and potassium. These conditions are only attained through careful attention to detail. The focus has to be on maximising orchard revenue rather than minimising costs.
APAL’s Future Orchards program is funded by Hort Innovation using the apple and pear industry levy funds from growers and funds from the Australian Government. AgFirst is a key Future Orchards partner.