The combination of NAD and NAA for thinning of ’Jonagold’ and ‘Idared’ apple trees

Abstract

Mature apple trees ‘Jonagold’/M.9 and ‘Idared’/M.9 were thinned with different concentrations of naphthaleneacetamid (NAD, - 25 ppm, 50 ppm and 100 ppm) at petal fall time, with 1-naphthaleneacetic acid (NAA, - 6 ppm and 12 ppm) at 10 mm fruitlet diameter and with their combinations sprayed in a sequence. On ‘Jonagold’, all single agent applications and all multiple sprayings of NAD + NAA thinned and increased the yield of fruit from bigger size class by 2-3 fold. Reduced total fruit number was compensated with better fruit growth so the yield per tree was not significantly decreased. Single applications of NAD thinned to the same extent as single NAA applications (for ‘Jonagold’ and ‘Idared’). A tendency of both thinners to produce stronger effect when applied in higher concentrations was observed on ‘Jonagold’. In comparison to single NAD or single NAA applications, no additional thinning was found on ‘Jonagold’ when the combination spraying of NAD + NAA was applied in a sequence. On ‘Idared’, all single applications of NAD or NAA as well as all their combinations slightly overthinned trees to the point that the yield of fruit > 75 mm was decreased. The remaining ‘Idared’ fruit grew so big that no significant total yield reduction was observed with the exception of the treatments with NAD 50 ppm or NAD 100 ppm in combinations with NAA 12 ppm which resulted in strongly decreased number of fruit. All thinning treatments on both cultivars enhanced flower formation for next spring.