The strongly biennial bearing characteristic shown by many bittersweet cider apple cultivars is demonstrated, and problems associated with this are discussed. Recent literature concerning factors associated with apple flower bud production and biennial bearing, and methods of control, is reviewed. Experimental investigations have examined a number of the latter for effectiveness and suitability in the context of current cider apple orcharding. Two methods involving low cost chemical sprays appear most promising, and may be combined for increased effect. Whilst either may be applied overall to whole trees to partially reduce fruit set, practical advantages are suggested for a system of part-tree cropping. One method consists of a single application of 1-NAA within 14 days of petal fall in the on-year to the lower branches of the trees, aiming to reduce fruit set on that portion to a very low level. Spray additions which improve results are described. The other method involves two applications of bromacil applied prior to flower induction in the off-year, which reduces the number of flower clusters in the ensuing on-year. Both methods have given satisfactory indications in first experiments using fully commercial application methods, and have been costed. Differences between some cultivars which affect the responses to and the success of treatments are discussed. Trees in poor health, showing low vigour and/or lacking minimal pruning are unlikely to respond satisfactorily. Some evidence of increased yields following the control of biennial bearing has been obtained, and in no case has cropping been reduced by satisfactory treatments on suitable trees. Indications concerning the balance between growth and cropping, the roles of plant growth substances, and the cause of biennial bearing on the experimental trees are discussed.
|Date of Award||1979|