Pollination has been a subject of discussion the last couple of springs.
There has been a lot of chatter about pollination issues because of poor fruit set and lower than desirable crop yields.
In some cases the poor pollination has been attributed to low bee activity (especially during cooler, wet weather) and flowering periods of early varieties out of synchronisation with other varieties for cross pollination.
Need to synchronise flowering
Dormancy breakers can’t influence bee activity but they can have a dramatic affect on synchronising the flowering periods of different varieties.
An emerging problem has been with early flowering varieties such as Pink Lady™ and Sundowner™ as their flowering period can start two to three weeks before another variety is flowering and available for cross-pollination.
This can lead to the abortion of flowers/fruitlets that were out early and result in low yields and reduced fruit quality because fruit has to be left bunchy to meet crop load targets.
It is worth noting that the best fruit comes from the king bloom which flowers first. If this fails to set then there is an over reliance on the secondary (lateral) flowers to set.
Best use of dormancy breakers
If the synchronisation of apple varieties for cross pollination, or compacting the flowering period, or obtaining higher prices for early harvest fruit, resonates with you, then it might be worthwhile considering dormancy breakers.
However, there are a number of things to consider before applying dormancy breaking products:
- the number of chill hours accumulated
- which product to use
- what rate
- application timing (late application of dormancy breakers can lead to dead buds and induce an uneven protracted flowering period)
- which varieties to treat.
Reasons for using dormancy breakers
1. Compacting the flowering period can be an advantage for chemical thinning varieties or blocks that have an extended flowering period.
Unlike Japan and some orchards in the USA where hand thinning of flowers occurs, we rely totally on chemicals for primary thinning during the spring.
Given that the king bloom flower provides the best quality fruit, chemical thinning aims to leave the king bloom set and remove the surrounding flowers. Having a uniform or compact flowering throughout the tree is required to achieve this.
2. Shifting the flowering period can help align the flowering period for different varieties to assist pollination.
There has been more interest in pollination recently because fruit set has been variable and unreliable as a result of cool/cloudy weather during the flowering period.
3. Shifting the budbreak forward can help bring fruit in for harvest earlier.
This can be an advantage for early market premium prices or as a tool for harvest management of large blocks.
Note that moving the flowering period forward may increase the risk of damage from frost in some areas.
4. When the chilling requirement is not met during dormancy. The ability to satisfy the chilling requirement is dependent on temperatures during dormancy, which varies from season to season and region to region.
This can result in trees having reduced fruit set and quality, distorted fruit, delayed foliation and extended bloom. Coastal and sub tropical regions are more prone to not meeting the chilling requirement of deciduous trees.
Products and application
The are many products that can influence bud break. Some of the better known products used as dormancy breakers include oils, potassium nitrate, Dormex® and Waiken®.
Local knowledge or experience is helpful in determining the application rates and optimal time to apply dormancy breakers.
The usual time of application is around 35 days prior to bud burst but does vary with different products.
Using previous bud burst dates together with the number of chill hours accumulated (calculated using local weather data) during the winter can be a good guide for anticipating bud break dates.
For more information on addressing your ‘rest breaking’ requirements, consult your technical expert.
For information and contact details, see the July 2012 Tree Fruit.
