Evaluation of alternative chemical thinning programs for apples

Variation between cultivars and seasons in reaction to chemical thinning and rest-breaking is large.  However, it was clear that there is a difference between Lift and Dormex in the bud break pattern observed.  The yield in Lift treated trees was higher than in Dormex treated trees which is a reversal of what was observed in the previous season.  An interaction with the chemical thinning program was also observed.  Especially important was the increased occurrence of malformed fruit in ‘Golden Delicious’ when Lift application was followed by GoldenThin/Promalin as a chemical thinning program.  This was enhanced when the rest-breaking treatment was applied after the optimum time and at the higher rate.  The alternative chemical thinning agents evaluated during the past three seasons were ATS and 6-BA.  The results with the ATS were disappointing and overthinning occurred and this is not seen as a viable alternative for the apple industry.  The results with 6-BA are promising.  6-BA on its own at either 100 or 150 ppm or in combination with NAA seems to provide good thinning effects.  At which rate it is applied and whether the product is used on its own or in combination with NAA  is dependant on cultivar and probably area.   All further research on these aspects will be funded by Valent BioSciences.