Harvest Management For Frost Affected Crops

These are:

1. Wider than normal range of fruit size and maturity both within the orchard block and also within the tree.
2. Lighter than normal crop and a wide variation in crop levels from tree to tree depending on the level of frost and stage in the biennial bearing cycle the block was in. There is also significant within tree variation with the lower tree very light while the upper tree is carrying a normal or even heavy crop.

The implications on harvest are:

1. Mixed maturity problems.
2. Increased risk of inherent vice problems, particularly bitter pit in Braeburn.

Mixed Maturity

This is expected to have a major impact on the Royal Gala types. Flowering was drawn out over a long period due to the cold spring and on many orchards there was a wide variation in timing between lower tree and upper tree flowering. In some instances this range of maturity is accentuated where dormancy breakers were used because the frost killed off most of the early flower and the cool spring delayed development of later flower on one year wood lateral flower bud which set heavily this year.

The upper tree fruit, and also lateral bud of one year wood fruit, is most likely to be 10 to 14 days later than older spur fruit which escaped the frost. On many blocks the upper tree fruit will be much later than lower tree fruit due to delayed bud break and flowering in the upper tree this year.

The implications for harvest are that careful selective picking based on maturity will be necessary. This means harvesting on a four to five day schedule.

Maturity will need careful monitoring using objective maturity testing. With the large variation in maturity likely between the upper and lower tree, it may be necessary to consider separate maturity testing for upper tree and lower tree fruit. Upper tree fruit tends to colour better so to the casual observer will look more advanced than the generally less well coloured lower tree fruit. This is why it is necessary to check its' correct maturity status through objective maturity testing. It is my expectation that on a lot of blocks it will not be necessary to attempt to harvest upper tree fruit at the time of the first two skim picks.

Braeburn can show a huge variation in maturity due to crop load. Trees with light crops tend to ripen their fruit well ahead of heavy crop trees. In those blocks with wide tree to tree variation in crop load expect to find those trees with light crops to show advanced maturity.

This year it's going to be necessary to train and supervise pickers carefully to make sue that lines with uniform fruit maturity can be presented for packing. Pickers will need a clear instruction on which fruit should be picked.

Inherent Vice Risk

The main problems here are likely to occur with the Braeburn group due to their susceptibility to calcium disorders such as lenticil blotch pit, and bitter pit.

The probability of problems from these disorders is directly related to tree vigour and crop load. Heavy crop, low vigour trees are low risk which light crop, high vigour trees are high risk.

In blocks where there is a variable crop load the trees should be categorized on the basis of crop load and tree vigour, then each vigour category sampled separately for fruit calcium analysis. This may help identify the boundary between acceptable risk and unacceptable risk on the basis of crop load level.

Some blocks are showing normal, or high crop load in the upper tree, and low cropping in the lower tree which was hit by the frost. Many years ago we looked at the incidence of bitter pit in light and heavy cropping parts of the same tree of the variety Cox's Orange. This study showed that fruit from the lighter cropping parts of the tree expressed higher levels of bitter pit than that from the heavier parts. It is our opinion that where cropping is variable within the tree, such as heavy cropping tops, and light bottoms, the fruit from the tops will carry much lower bitter pit risk than that from the bottom of the tree.

Fruit from trees in the high risk category, and parts of the tree with light crops should be harvested separately from the export fruit lines. It is probably best to take this fruit off prior to the export pick when there is less pressure on harvesting labour such as in the harvesting gap between the Royal Gala and start of export Braeburn.

Another way to check the storage risk of a marginal line of fruit may be to harvest a sample about a week ahead of export and then accelerate its' ripening. Dipping the sample in 3000 ppm Ethrel. and holding for 14 days at ambient room temperature will ripen the fruit rapidly. We tried this many years ago but have not developed the technique any further. To be able to interpret the results it's probably necessary to take a check sample from a low risk heavy cropping block to calibrate the technique against.

In some countries a similar technique based on magnesium infiltration has been developed for the same purpose. To the best of my knowledge this technique has not been tested here.