A study of the effects of size-controlling rootstocks on spurring, blooming and fruiting habits of two apple varieties

Size controlling apple rootstocks have been known and used for centuries. At present, there is considerable interest in smaller than standard size trees because they allow almost all orchard operations from pruning to harvesting to be done easier and perhaps with less labor. The smaller trees also present more opportunity for mechanical harvesting. Some methods besides rootstocks that may be used to dwarf apple trees are as follows: (1) scoring or ringing the trunk, (2) scion variety selection such as spur types, (3) chemicals such as Alar or B-9, (4) severe pruning, (5) low fertility levels, and (6) site selection such as shallow, infertile or sandy soils. Although all these methods have potential, dwarfing by rootstock is most satisfactory at present. Dwarfing of apple trees offers possible improvement in fruit color and fruit characteristics. Evidence indicates dwarf trees are more open than standard trees. This makes possible more efficient use of sunlight. Therefore, more sugars may be manufactured with better fruit color resulting and more spurs developing. Openness of the tree is probably related to Auxin factors which relates to branch angles. Apple flowers are usually formed from buds on short shoots known as spurs. Spurs are usually formed from leaf buds on wood in its second growing season. Spurs usually produce flower buds the year they are formed and every other year thereafter. Fruit set usually occurs with blooming. Annual production is related to numbers of live vigorous spurs on various aged wood throughout the tree and the fruiting of these spurs. Past studies with dwarfing apple rootstocks have been on tree size, yields and performance of scion varieties with various soils and climates. The objectives of this investigation were to determine the effects of eight size controlling rootstocks on leaf bud numbers, and number of spurs developing, blooming, and fruiting on wood of various ages.