L.D. Tukey
The cost of producing apples has risen sharply in the last years. The greatest increase has been in orchard overheads, which now appears to represent over 50 % of total costs. Returns also have increased, but not as much as total costs. Thus, to meet rising costs, the production of premium-valued fruit must be increased, especially on an annual basis.

There have been several approaches to increasing productivity. One method has been to design orchards for greater potential productivity by maximizing the volume of the bearing mantle and increasing fruit density in this volume. For annual cropping there needs to be a balance between fruiting buds and vegetative buds. Although regulation and control can be achieved by proper pruning and training, this can be made easier by the inclusion of growth regulators in the management practices for intensive orchards. Two potential regulants are Alar (succinic acid-2,2-dimethylhydrazide) and Promalin (a mixture of gibberellic acid A4 + A7 and benzyl adenine). A possible third regulant is NAA (napthaleneacetic acid). In research these have been used singly or in combination, and applied from early bloom to 30 days after bloom.

Alar was used to increase return bloom and to inhibit vegetative extension slightly, as an annual application. Promalin was used not only to increase the typiness of Delicious, but also to increase fruit weight and yield of apple cultivars by lengthening the fruit. In addition, Promalin was used to counter the fruit flattening action of Alar. NAA was combined with Alar to enhance return bloom when Alar was used at a low concentration to lessen the flattening effect of a spring application. Treatments were applied to trees in intensive orchard plantings, especially the Penn State low trellis hedgerow.

Promalin 25 ppm at full bloom, or Promalin 12,5 ppm at full bloom and again at calyx to calyx closing, has lengthened fruits of several apple cultivars. In some cases the split rate and timing have been better than a single full rate. Yield has not been substantially increased, but overall size-packout has been increased. Alar 1 000 ppm at 30 days after full bloom in even years and Promalin 25 ppm at full bloom in odd years have tended to bring fruits back to the length of non-treated fruits, but fruits tended to be smaller than the non-treated. Overall yield benefit was questionable for this treatment.

The mixture of Alar 500 ppm and NAA 5 ppm applied annually at 50 days After full bloom (shoots 15 to 30 cm) appeared to give the highest repeatable

Tukey, L.D. (1981). ALAR AND PROMALIN IN INTENSIVE ORCHARD SYSTEMS. Acta Hortic. 114, 152-153
DOI: 10.17660/ActaHortic.1981.114.18

Acta Horticulturae