Evaluating the potential of plant growth regulators to limit plant growth on tree and hedging species

Benefits to Industry:

Field grown stock is graded by height, so excessive growth can result in stock exceeding height specifications. This can result in extra cost where stock has to be cut back, reductions in profitability, or increased wastage where cutting back is not a feasible option (particularly where stock is destined to be sold as a tree).  Increased control of crop growth and more uniform crop height is thought to reduce grading costs by 5%. Improved growth control should reduce the percentage of stock exceeding 90cm (the maximum transplant height required by the forestry sector); resulting in increased marketability of the crop. As growers within the tree and hedging sector have their own sprayers or use contractors to apply plant protection products, the application of plant growth regulators would not require additional capital investment.

Aims and Objective:

1. To determine optimum rates and growth stages for the application of growth regulators suitable for use to manage growth of cuttings and transplants of tree and hedging species.
2. To evaluate optimum rates of chlormequat (Stabilan 750) & trinexapac ethyl (Cutaway) on key field grown HNS species
   1. To quantify the effectiveness of tank mixing (Stabilan 750) & trinexapac ethyl (Cutaway) for their effect on growth of two field grown deciduous transplanted species (Alnus & Betula). 
   2. To investigate the use and optimum timing of plant growth regulators on transplants and one cutting raised subject to prevent excessive growth. 
   3. To identify any negative effects of the use of these plant growth regulators.
   4. To produce an article for HDC news which summarises and promotes the results of the experimental work.
   5. To organise a nursery based open afternoon to allow growers to view the results at the end of the growing season, prior to lifting. This could be part of a wider technology transfer day for producers of field grown stock as provisionally discussed with Wayne Brough (if required by HDC/the industry)