South African experience
In most areas where apples and pears are growing in South Africa, the trees do not get enough winter chill to break dormancy satisfactorily. This results in delayed foliation, a protracted bloom period and poor yields.
A great deal of research has been done on rest breakers and South African researchers are at the forefront of this research.
Below is a list of fundamentals and materials developed in South Africa for good rest breaking results that orchardists can use in Australia when it is suspected that their apple and pear trees do not get enough winter chill.
Good tree health is critical for successful rest breaking.
•Need good quality, strong healthy buds.
•Too heavy crop load in the previous season makes it very difficult to achieve good rest breaking.
•Post-harvest fertiliser is very important to build up reserves. Fertiliser, especially nitrogen, should be applied from April 1 and must be completed ideally by mid-April, but not later than the end of April.
For late apple varieties, such as Granny Smith, Pink Lady and Sundowner, fertiliser can be applied before harvest (there is no risk of nitrogen being translocated to the fruit).
•Post-harvest foliar nutritional sprays are very important, especially where tree roots are not functioning well because of drought, Woolly Apple Aphid damage etc. Foliar nutritional sprays must be applied from mid-March and be applied immediately after harvest thereafter.
•Irrigation is very important to achieve good tree health status. It may be necessary to irrigate lightly in winter to prevent killing off hair roots. Soil moisture must be monitored regularly.
•Remember that it is very difficult to wake up a sick and stressed tree.
Warm weather after applying rest breaking sprays is very important
•Have your spray cart ready if weather forecast predicts three days of warm sunny weather, and spray immediately so that buds can sweat under the oil film.
Application points
•Spray to point of run off.
•70% of tree row volume is usually sufficient.
•Direct at least two–thirds of spray to the top half of trees.
Spray products to use
•Fruit growers in South Africa commonly spray twice. The first spray, six weeks before anticipated bud swell, is applied to the entire tree or just the tops of the trees with a 3% Dormex solution, followed a week later with 4% winter oil plus 1% Dormex solution.
This works particularly well on high chill varieties such as Golden Delicious.
On varieties of apple and pear that require less chill, the second application can be 3% oil plus 0.5% Dormex.
•Apply low biuret urea 14 to 31 days after the oil spray. Recommended rate is 500g per 100 litres water for pears, and 1000g per 100 litres water for apples.
A high dose of nitrogen helps the buds to come out of rest quicker after the oil spray. Low biuret urea must contain less than 0.4% biuret.
•A common practice is also to apply the high rate of urea 7-10 days before the oil spray.
•High urea sprays in autumn will also build strong healthy buds for the following season.
•Potassium nitrate can be used as a supplement (to top-up initial program), 21 days after oil spray, at 3 kg/100 L water. Can repeat application seven days later.
•Apply 25 kg zinc sulphate hepta hydrate (23% Zn) per 1000 L water to apple and pear trees before oil together with low bio urea. Low zinc values will increase the incidence of delayed foliation.
The responses to the specific rest breaking recipes with the above products can differ from region to region, from orchard to orchard, and from variety to variety. A continuous program is recommended so that the trees get used to it.
See this article in Tree Fruit July 2018
