Undercutting during the growing season is the main way producers control the growth of field-grown trees and hedging but effectiveness is determined by the weather. HDC project HNS 187 investigated various chemical plant-growth regulators as possible alternatives.
Fargro Chlormequat (chlormequat), Regalis (prohexadione calcium) and an experimental product were tested on species including Alnus glutinosa, Betula pendula, Populus x canadensis 'Robusta', Prunus avium and Sorbus aucuparia.
All were applied as a foliar spray, with the experimental product also applied via a "weed wiper". All the products were used at the maximum label/EAMU rate to ensure the target level of growth control was achieved.
Results so far show Fargro Chlormequat the most effective growth regulator on alder, beech and poplar, but it caused excessive stunting on sorbus. At the rates used, it also caused leaf yellowing on all species.
Applied as a foliar spray, the experimental product was the most effective on cherry and had some effect on sorbus, but there was no significant growth reduction when applied via the weed wiper. Regalis had some effect on cherry and sorbus.
The second year of the trial (2014) focused on minimising phytotoxicity - reducing the rates of Chlormequat to minimise leaf yellowing while aiming to achieve a useful level of growth regulation. Treatments have also been refined to reflect the species' different responses.
Horticultural Development Company
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