Project number
P04000236
Project leader
Halleen, F
Institution
ARC Infruitec-Nietvoorbij, Stellenbosch
Start date
2019
EXECUTIVE SUMMARY
Objectives and Rationale
The study aimed to determine the effect of mechanical pruning (MP) on the occurrence of grapevine trunk disease pathogens compared to conventional hand pruning (HP).
Methods
During the dormant seasons of 2019, 2020, 2021 and 2022, selected vineyards in Robertson, Goudini / Aan de Doorns, Vredendal and Upington were hand or mechanically pruned. From the mechanically pruned vines (MP), 10 pruning stubs plus at least 4-5 years older growth were removed (as one intact piece). In the hand-pruned vineyard (HP), the distal spur, together with ~10cm of the cordon were removed. Fungal isolations were conducted from samples, and the pathogen incidences and severities were determined.
Key Results
In general, HP vines had significantly higher incidences and severities of aggressive canker and dieback pathogens, especially wood-rotting Basidiomycetes, Botryosphaeriaceae, Togniniaceae, and Diatrypaceae (only in 2019). Very few basidiomycetes were observed in the mechanically pruned vines; however, they were abundant in the HP vineyards.
Key Conclusion of Discussion
Mechanical pruning is a viable option to limit the effect of trunk pathogens and increase the lifespan of the vineyards. The explanation for the higher incidence in hand-pruned vines could be two-fold, firstly, the hand-pruned vines had larger wounds. This is likely due to the technique of conventional hand pruning, which generally cuts back to two-bud spurs, resulting in “severe” cutback of spurs to prevent the build-up of old wood, creating larger wounds. Secondly, the length of the two-bud spur is significantly shorter in hand-pruned vines, and the pathogen only has a short distance to colonise before it reaches the older wood of the spur and cordon, where it can colonise and kill the wood. Even though mechanically pruned vines have more wounds since there is a larger number of shoots and wounds can be uneven and jagged, the wounds are smaller, further from the older wood, and the longer canes give the vine more opportunity to compensate when infection occurs.
Take Home Message for Industry
Mechanical pruning could increase the lifespan of vineyards to complement other benefits of MP, like reduced labour costs, increased yield and acceptable or increased wine quality. However, mechanical pruning is a good alternative to hand pruning if vines have sufficient vigour and are trained on the correct trellis system. The larger crop load and expanded growth above ground require more water and fertiliser to apply mechanical pruning sustainably. Additionally, mechanically pruned vines must be mechanically harvested. For these reasons, hand-pruned vineyards should not be converted to mechanically pruned vineyards. Preparation is key. Before considering mechanical pruning, ensure that you have the correct trellis system, row spacing, rootstock-scion combination, etc. and consult experts in the field.