Researchers are assessing the value of dormancy–breaking sprays to help growers encourage compact and uniform flowering in their apple orchards when it’s just not cold enough for the trees to do it on their own.
The use of dormancy-breaking sprays could help apple and pear growers adapt to warmer years because dormancy breakers can stimulate earlier, more homogenous bud burst and flowering in a number of crops grown in mild climates worldwide.
There is also some evidence that these products reduce the length of the harvest window by inducing a more compact flowering period.
In the 2015–16 season, a trial was undertaken in Gala apple trees at three locations (Queensland, Western Australia and Tasmania) to assess the efficacy of using dormancy-breaking sprays under current Australian climates and, the potential to use these sprays as an orchard management adaptation to inadequate winter chill under future Australian climates.
The trial compared the effect of Waiken®, Dormex® and Erger on the timing of green tip and flowering, the duration of the flowering period, fruit set, yield, harvest time and variability of maturity at harvest.
Spray application
Getting the timing right for dormancy-breaking spray applications is important, but can be difficult as growers need to estimate the green tip date.
The aim in this trial was to spray all products at around 35 days before green tip. Historical records, together with in-season chill accumulation calculations, were used to predict green tip date.
By comparing the current season’s chill accumulation curve with that of the previous few seasons, a best estimate of green tip date was determined. However, the actual spray date was then further dictated by the weather. All products were sprayed at the label rate and there was no phytotoxicity observed.
Green tip & flowering
The impacts of the dormancy-breaking sprays varied between sites.
In Queensland, all sprays advanced green tip and flowering, and resulted in a more compact flowering period.
Dormex treated trees were significantly different from Waiken and Erger treated trees, while there was no difference between trees sprayed with Waiken and Erger.
Dormex advanced green tip and flowering, and caused a more compact flowering period in Western Australia. Waiken advanced green tip but had no effect on the full bloom date, and actually increased the duration of the flowering period.
In Tasmania, Dormex and Waiken delayed green tip, but did not affect the timing of full bloom, or the length of the flowering period. This delay in green tip is possibly a result of the much higher level of accumulated chill at that site. Unseasonably hot weather just prior to, and during, the flowering period also significantly reduced the length of the flowering period in all trees.
Fruit set, yield & maturity at harvest
Fruit set was not significantly different between treatments at any location indicating the compaction of the flowering period did not negatively, or positively, impact the effectiveness of pollination.
In Queensland, fruit maturity was advanced in trees treated with Dormex, Erger and Waiken compared with untreated trees, reflecting the difference in flowering dates.
(continued next month)
See this article in Tree Fruit August 2016
