Establish the effect of rest breaking agents on vegetative and reproductive development of apples in the Koue Bokkeveld and Witzenberg valley

The objectives of this project were to establish the effect of rest breaking agents on the duration of bud break and flowering, effectiveness of chemical thinning, variance in fruit harvest maturity and long term yield of ‘Golden Delicious’ and ‘Cripps’ Pink’ apples in the Koue Bokkeveld and Witzenberg Valley.

The following rest breaking treatments were applied to the same ‘Cripps’ Pink’ and ‘Golden Delicious’ apple trees from winter 2011 through to winter 2013: 3% oil, 6% oil, 4% Lift and, 0.5% Dormex + 4% oil.  Rest breaking treatments were compared to an untreated control in terms of vegetative and reproductive bud break, bloom duration, yield, fruit maturity and fruit quality.

Richardson chill units (May-Aug) exceeded 1600 in all three years and would therefore be considered to be sufficient for apple production without the need for rest breaking application

2011: 0.5% Dormex in combination with 4% oil condensed both vegetative and reproductive bud break in both cultivars.  Yield data could unfortunately not be assessed.

2012: Lift at 4% seemed to increase and condense vegetative bud break in ‘Cripps’ Pink’, while 3% and 6% oil were able to condense flowering.  Production was not affected by treatments.  No treatment effects were observed on Golden Delicious.

2013: 4% Lift advanced the onset, condensed and increased vegetative bud break. 0.5% Dormex + 4% Oil and 6% oil also increased final vegetative bud break compared to the control.  0.5% Dormex + 4% oil seemed to advance the onset of flowering compared to 3% oil and 4% Lift. 6% oil increased yield and yield efficiency compared to 4% Lift and the control. 3% oil also increased yield efficiency compared to the control. Treatments did not significantly affect cumulative yield over the 2013 and 2014 harvests. Fruit size was not affected while effects on maturity were slight. Treatments did not affect the flower cluster density in 2014.

4% Lift and 0.5% Dormex + 4% oil advanced the onset of vegetative bud break in ‘Golden Delicious’. Lift also increased bud break and decreased the percentage latent buds. 3% oil increased yield and yield efficiency compared to the control. Treatments did not significantly affect cumulative yield over the 2013 and 2014 harvests.  Trees that received 4% Lift as well as 0.5% Dormex and 4% oil over the preceding three years showed increased flower cluster density in 2014 compared to other treatments.

Despite accumulation of >1,600 Richardson chill units, rest breaking treatment improved bud break in all three years in ‘Cripps’ Pink’ and in two years in ‘Golden Delicious’.  Not all rest breaking agents where equally effective – 0.5% Dormex plus 4% oil was effective in 2011 and 2013 while 4% Lift was effective in 2012 and 2013.  The cumulative effect of treatments over the three years started having a positive effect on yield in 2013/14, possibly by increasing bearing positions.  Based on these results, we recommend that Koue Bokkeveld growers seriously consider the application of rest breaking agents.