Browsing by Author "Truter, Werner Van Heerden"

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    Management practices to improve quality of apple nursery trees in containers
    (Stellenbosch : Stellenbosch University, 2019-04) Truter, Werner Van Heerden; Theron, K. I.; Steyn, Wiehann J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: The quality of nursery trees at planting has a significant effect on productivity during the early years of newly established orchards. Trees need to grow and fill their allocated space in the orchard as quickly as possible for optimal return on investment. One of the main concerns when establishing new orchards is the quality of nursery trees as well as the prolonged establishment period commonly referred to as transplant shock. Transplant shock occurs due to damage to the root system, which is aggravated by an imbalance in root to shoot volume. Different management practises and timing of these practises were evaluated on containerised apple nursery tree. The practises focussed on growth cessation and hardening-off, nitrogen reserve build-up, and defoliation. The effect of these management practises as well as different planting times and methods on spring bud break and new growth during the first growing season in a commercial orchard was investigated. Prohexadione calcium and abscisic acid showed no significant effect on growth cessation during the nursery phase, and no significant effect in spring bud break or new growth in the orchard. Trees planted in autumn showed earlier bud break whereas trees planted in spring had a higher bud break percentage. Foliar nitrogen (urea) during the nursery phase did not significantly affect spring bud break and new growth. At the rates applied, foliar copper, in comparison to 1-aminocyclopropane-1-carboxylic acid proved to be a more successful chemical defoliant in the nursery with no significant negative effect on the subsequent performance in the orchard. Dormancy management practises improved bud break in spring as well as the architecture of young trees planted in a commercial orchard. It is recommended that trees receive a six-week 6 °C cold storage period and a chemical rest breaking treatment to improve establishment. Different planting methods of containerised nursery trees did not significantly influence bud break in spring, but planting containerised trees with an undisturbed growing medium or only slightly loosening the growing medium before planting improved new lateral shoot growth and apical extension growth. Producing “feathered” single or double-leader apple nursery trees in containers proved to be difficult. Either the container was too small, thus restricting the root volume too much, or the rate and number of plant growth regulator (PGRs) applications were not enough. No clear conclusion could be made on the use of PGRs to harden-off trees or chemical defoliants in our trials. Trees planted during autumn, in a warm winter region, did not accumulate sufficient chilling, which resulted in reduced bud break during spring. This time of planting resulted in a basal dominant tree architecture. As trees were probably not managed ideally in the orchard, the treatment effects could have been masked by a lack of tree vigour during the first growing season in the orchard. A period of a six-week cold storage at 6 °C as well as a chemical rest breaking treatment are important dormancy management practises, regarding spring bud break and tree architecture, when trees are planted in warm regions. Because containerised nursery tree propagation is a new concept in South Africa, further research is needed on propagation and subsequent management of these trees.