Late season Vigour management – Have you got the tiger by the tail?
By Meg Becker
Balancing shoot growth (vigour) is critical to good fruit production. Leaves supply all the energy for tree growth and fruit development, but shoots are greedy and excessive vigour will limit fruit size, yield, and quality.
Deficit irrigation. The first sign of water stress (before impacting fruit size) is the termination of vegetative shoots. This is a common practice, however, should be carefully managed so as not to impact fruit quality outcomes.
Summer pruning has multiple benefits, letting light into the canopy which improves fruit colour and sets buds up for next season. Removing shoots that generate carbohydrate that is not being partitioned into cropload reduces tree vigour.
Cropload is the most effective form of vigour management in any canopy system, however, achieving appropriate croploads in a high vigour block can prove challenging. Altering the leaf to fruit ratio helps improve vigour responses.
Plant growth regulators (PGRs) are an effective tool for managing vigour. Ethephon (Ethrel) and Prohexadione-Calcium (Regalis) are the two most broadly used in pipfruit.
Regalis suppresses growth-promoting plant hormone synthesis resulting in shorter internodes (shorter shoots) and less vigour within the plant in that growing season.
Ethrel is often used as an alternative and supports return bloom (important in a high vigour canopy).
These two products may be used in unison in excessively vigorous blocks.
Post-harvest pruning cuts can made while the tree is still in leaf. In doing this, the carbohydrate reserves are removed from the tree prior to senescence – managing the vigour response at the start of the next growing season. If you miss this window or need to spread labour, pruning at full bloom can be just as effective, this can also be beneficial in blocks where you need to ensure flower numbers prior to branch removal.
Summer girdling can decrease vigour and improve fruit size and return bloom when done correctly. Girdling can be carried out from petal fall through to the end of November/early December. The efficiency of girdling diminishes later in the season.
The depth of the girdle determines success in vigour management. The bark, phloem and cambium tissue should be removed down to the hard white xylem tissue.
Two opposing half C cuts, overlapping and, approximately 50mm apart – the closer the cuts, the harsher the girdle.
As a last resort, root pruning may be used when a block is completely out of control and everything else has failed. Root pruning is harsh, and after the last there wet seasons would be a last resort. Root pruning is also known to reduce fruit size outcomes.
