Post-harvest orchard management
Although there is still another month of the apple harvest to go, now is the time to begin setting the orchard up for next season.
These days we are placing a lot of emphasis on growing firm, crunchy, tasty, high coloured fruit. To achieve this objective, trees need to be calm, low vigour and hungry. Towards harvest there needs to be low nitrogen status with leaf nitrogen levels downs to 2% or even slightly under. Leaves need to be pale green, not dark green but still be in top condition.
For adequate spring growth flush and satisfactory fruit set, nitrogen levels need to be restored to normal before leaf fall.the post-harvest fertiliser programme is critical.there also needs to be a good environment for root growth as well to enable the nutrients to be taken up.there is very good research data now to indicate that for root nitrogen uptake the foliage needs to be actively photosynthesising so there is not a lot of nutrient uptake going to occur once the leaves begin to senesce and fall.
The spring growth flush is dependent on mobilisation of stored reserves and there is little uptake of nitrogen from the soil in spring until the stored nitrogen reserves have been used. Uptake from the soil usually commences about six weeks after bud break.
Post-harvest foliar nitrogen applications are capable of supplying up to 50% of nitrogen requirements, and compared to soil applications are at least twice as efficient. Leaf uptake is rapid, and nitrogen applied as foliar tends to accumulate in flower buds and annual shoots rather than the roots. Postharvest soil applications are largely stored in the roots, with little making its way up to the buds until spring.apply several post-harvest foliar applications of Urea at 2–3% concentration, 10–14 days apart well before leaf fall to minimise the adverse effect foliar nitrogen applications could have on European Canker control.
Adequate spring nitrogen leaf levels, usually around 2.8–3% in spring leaf samples are necessary for satisfactory fruit set. Where there is concern in regard to adequate spring nitrogen levels, foliar nitrogen sprays in the pre-flower period can be applied to lift spring nitrogen levels. The nitrogen fertiliser programme needs to be a combination of foliar and soil applications. Soil applications need to be targeted at times when there is efficient uptake, i.e. in the autumn well before leaf fall, or in the spring four to six weeks after budbreak. Spring dressings are generally only necessary where tree vigour is poor because excess available nitrogen at this time can depress fruit colour development as well as lead to soft fruit.
Many orchards now have micro irrigation systems capable of fertigation. Fertigation is a very efficient way to apply fertiliser. In deep, fertile soils with good drainage, established apple tree roots are able to tap deep soil water supplies. Because most of soil organic matter and soil nitrogen supply is largely confined to the top soil layers, minimising water uptake from the upper soil layers over most of the growing season will lower fruit nitrogen levels leading to very good fruit quality, particularly in regard to fruit colour and firmness.
Our soil moisture monitoring shows that for high quality soils with deep rooting, it is not necessary to irrigate these soils until well into the summer period. This strategy minimises pre-harvest growing season nitrogen uptake, leading to low
fruit nitrogen status. Incidentally, there is some research data from pears which shows that nitrogen soil applications within a month or so before harvest does not influence fruit nitrogen levels.this probably applies to apples too.
Over the summer, there can be quite a build-up of soil available nitrate, particularly in dry climates. Once autumn rains occur roots become active through the whole soil profile, so there will be significant nitrogen uptake from that already available in the soil. These days there are nitrogen test kits available for measuring soil mineral nitrogen levels. These are Kwik N Test strips. A recent Sustainable Farming Fund (SFF) project investigated available soil mineral nitrogen in vegetable and arable cropping land and found that by measuring soil nitrogen and taking it into account, nitrogen fertiliser rates could be substantially reduced with little effect on yield. As excessive nitrogen has such a huge adverse impact on tree fruit quality, these test strips look like a useful tool for determining the need for nitrogen fertiliser on orchards.
Our general impression is that nitrogen use in orchards is not all that efficient and often well in excess of requirements due to inappropriate timing for efficient uptake.we can do a lot better for the environment and our fruit quality by fine tuning nitrogen fertiliser programmes.
Check drainage systems and where necessary carry out maintenance before soils become waterlogged in the winter. In recent years, heavy rain in late winter or early spring has been a feature of the climate in our fruit growing districts.
Where drainage is inadequate, trees suffer poor root health, leading to high stress levels and increased disease and nutrient deficiency incidence. There is good data linking pipfruit susceptibility to European Canker and also fireblight to poor drainage. In summerfruit, bacterial blast incidence is higher where trees are under stress.
Autumn is the time to address drainage and compaction problems. Some soils are prone to compaction problems, leading to perched water tables. Providing there is free draining soil underneath the compacted layer, deep ripping will solve the problem. For maximum effect, soils need to be very dry at time of ripping to amplify the shattering effect.
Where drainage is poor, deep ripping may not solve the problem and can make it worse if the compacted layer is preventing subsoil water rising to the surface. Where mole drainage is part of the drainage system, autumn is not the time
to renew the mole drains. Mole drains should be pulled in the late spring when the subsoil is drying out and has reached the stage when the clay through which the mole is being pulled will give a glazed surface. Incidentally, pale foliage in early spring may not indicate nutrient deficiency. Often it is chill injury, particularly in frost tender plants. Chill symptoms normally disappear after a few days of warm weather.
We have also observed through our soil moisture probes that deep, well drained soils with high moisture holding capacities do not need much supplementary irrigation for well established, deep rooted tree fruits.
PEST AND DISEASE MANAGEMENT
As a general rule, application of insecticides in the postharvest period is not necessary. In our Integrated Fruit Production (IFP) programmes the predator population will mop up most insect pests.the only exception to this rule I can think of is pear/cherry slug which can be a problem in pears and cherries. This insect can quickly destroy leaves if it goes uncontrolled, with adverse effects on the next season’ s crop. It is very susceptible to insecticides including summer oils, so is easily controlled.
Fungi and bacterial diseases require post-harvest control. In pipfruit European Canker is the main disease of concern. On arrival of autumn rain, conidia spore production where the disease is present becomes rampant and can readily infect picking wounds and leaf scar tissue, both of which are major entry points for this troublesome fungous disease. As well as controlling European Canker, post-harvest fungicides also do a pretty good job of reducing the build-up of black spot inoculum in those varieties, such as the gala group which tend to have an autumn growth flush.
Autumn is a very active period for Phytophthora root rots, so in situations where these root rots are likely to be troublesome, a post-harvest phosphorous acid spray should be applied. Summerfruit need post-harvest disease control for brown rot and bacterial diseases.
In the case of brown rot, any unharvested crop is likely to become infected, and this infection moves from the fruit into the wood where it establishes a lesion that becomes a source of inoculum for blossom and fruit infection next season. Any fruit remaining on the tree after harvest should have been removed to prevent the brown rot fungus entering the wood. Where brown rot lesions have become established, these should be pruned out in the autumn while they are easily seen, to minimise disease carryover.
Where labour resources are available, trees should be pruned in the post-harvest period.at this time silver leaf susceptibility is lowest due to hot, dry weather and the tree sap flow is least favourable for the silver leaf fungus to establish. Pre-leaf fall and leaf fall copper sprays are necessary in summerfruit to protect leaf scar tissue from bacterial infection.the objective is to prevent bacterial populations, which are always present in the orchard, from reaching the critical mass necessary for tissue invasion. The first copper spray, usually at a relatively low rate, just as leaf fall is commencing.this spray should be followed by several more at higher rates, with the final one coinciding with the end of leaf fall.
Incidentally, copper is very poisonous to sheep and other grazing animals, so sheep grazing of orchards where a leaf fall copper spray programme has been applied needs to be delayed for six to eight weeks or more until any copper residues in the sward have dissipated, otherwise you will have a crop of dead sheep on your hands.
Where labour resources are available, the post-harvest period is a good time to address excessive vigour and shading problems in the earlier harvest pipfruit varieties.this mainly involves complete removal of large, excessively vigorous branches high in the canopy. Their removal at this time has an overall effect of reducing the amount of photosynthate being translocated to the rest of the tree to fuel next year’s excessive vigour problem, as well as lifting light levels in canopy to improve the quality of next season’s fruit buds.
It is not necessary to attempt detailed pruning at this time. What is needed is a quick pass with a chainsaw, taking out two or three branches per tree. John Wilton is a deciduous fruit specialist with Agfirst.