Articles
NEW REST-BREAKING AGENTS FOR THE CONTROL OF DELAYED FOLIATION OF APPLES
Annual production of fresh fruit totals 600000 tonnes of fresh fruit are produced annually, 90% of which are apples, most of which are exported (Unifruco, 1989). Situated at 180W and 340S, this region may be regarded as marginal for the production of high chill apple cultivars.
If the climatic suitability of the major production areas is characterised by Richardson Chill Units (RCU), it is found that the major apple producing region receives only 50% of the chilling required to completely satisfy the crops cold requirement (Matthee, 1982). The many microclimatic zones that characterise the W. Cape further complicate the selection of production sites suitable for fruit production, thus the interest in climatic modelling.
The insufficient winter chilling and hot dry summers lead to abnormal plant growth generally referred to as delayed foliation (DF) (Black, 1952). Some characteristics of DF are insufficient blossom synchronisation between cultivars and pollinators, abnormal growth and bearing, and poor and uneven fruit-size.
For fruit production to be profitable the extent of these abnormalities has to be reduced.
Management techniques such as the application of chemical rest-breaking agents and physical manipulation are extensively used (Saure, 1985).
For more than 20 years commercial chemical control in pome fruit orchards has depended on the use of DNOC/oil, a relatively cheap and effective compound applied during late winter as a full cover spray.
However, the response is not only erratic, but the potential banning of this toxic compound and our dependence on exports necessitates the introduction of new, more ecological-friendly rest-breaking agents.