Chemical thinning influence on ‘Golden Delicious’ apples Fruit number
|Fruit thinning is a common agricultural practice in apple orchards, necessary to ensure profit|
|Omer Crane, Ayelet Sar Shalom, Yuval Ogny, Northern R&D MIGAL, Galilee Technology Center|
|September 14, 2018|
Results and discussion:
Fig 1 - Percentage of persisting fruit in 3 successive years
In 2012 and 2013 the second thinning treatment was with BA and in 2014 with Dilamide. Percentage of persistent fruits was the same (30%) for the control trees in 2012 and 2013 and natural fruit drop was more severe in 2014 with only 20% persisting fruits. In 2012 the effect of the first thinning was milder compared to 2013 and 2014 with 17.4%, 8.8% and 12% persisting fruits, respectively. Accordingly, in 2012 the second thinning lead to further fruit dropout and the rate of persisting fruits was 12% while in 2013 and 2014 no further fruit dropout was evidenced.
Therefore, it can be concluded that both thinning treatments will lead to ˜10% persisting fruits and further decline is not expected. If the reaction to the first thinning treatment is mild, advanced thinning is expected in reaction to the second one. But if a rate of 10% persisting fruits was already obtained by the first treatment, no further fruit drop is expected. This phenomenon is permanent even when natural fruit drop is high.
Table 1 - Average number of fruits per tree
This phenomenon had an influence on the final fruit size and fruits harvested in 2014 were small as can be seen by comparing fruit size distribution between years (Fig 2).
Fig 2 - Fruit size distribution at harvest after 2 thinning treatments at 3 successive years
Since final fruit size that is preferred by the marked in 70 millimeter in diameter it can be concluded that for the current ‘Golden Delicious’, grafted on M9 rootstock trees, 300 fruits per tree is the preferred number for desirable size. This number has no influence on alternate bearing since decrease in return bloom has been observed only when fruits number per tree was above 580 (Fig 3).
Fig 3 - Percentage of return bloom
From integrating the data above, it was assumed that since percentage of persisting fruits was the same after thinning in all years and fruit number per tree was variable, inflorescence number at bloom is the key factor for determining chemical thinning effect. During 2015 and 2016 we have evaluated inflorescence intensity (see Material and methods) as representing inflorescence number and determined its effect on final fruit number at harvest after chemical thinning (Fig 4).
Fig 4 - Correlation between inflorescence intensity and fruits per tree
A Significant correlation (R2>0.5) between inflorescence intensity and fruit load at harvest was found for both FB and FB+14 thinning treatments (Fig 4). From analyzing the obtained data, it can be concluded that Agriton thinning will not lead to over thinning (fruit number lower than 300 per tree) when inflorescence intensity is under 2 (very low). A second thinning will not lead to over thinning when inflorescence intensity is lower than 3.