ASHS 2015 Annual Conference

The adoption of high-density orchards during the last decade has resulted in a significant improvement in yield and fruit quality. With the use of highly feathered trees, important yield can be achieved in the second and third years after planting, which is an essential asset to help pay for increased tree numbers and establishment costs. As the benefits of highly feathered trees were discovered, it became necessary to develop nursery management techniques to stimulate lateral branch development. The number of feathers on U.S.-grown nursery trees has also improved significantly in the last decade. Prior to 2009 most nurseries used a single spray of Promalin combined with leaf removal to obtain trees with three-to-five feathers. MaxCel, a cytokinin plant growth regulator already labeled for several uses on apples, was registered for chemical branching of nursery apple trees in 2013. To further study the use of MaxCel and Promalin to induce lateral branching, we conducted four nursery branching studies in Washington State (2012 and 2013), Pennsylvania (2013) and Chile (2012/2013). To reduce flowering in the first year after planting and susceptibility to fire blight, the effect of Gibberellin sprays in the nursery was evaluated on 'Gala' and 'Pink Lady' apple trees in Washington State (2013). There were significant variety effects with 'Gala', 'Fuji', 'McIntosh', and 'Empire' producing more lateral branches compared to 'Macoun' and 'Cameo'. Maxcel and Promalin both induced significant numbers of feathers. The number of feathers increased linearly with increasing number of sprays from six feathers per tree up to 20 feathers with five sprays. There was little difference in the two rates of Maxcel and Promalin (500 mg/L and 1000 mg/L). However, Maxcel at 1000 mg/L induced more feathers than Promalin or Maxcel at 500 mg/L. Promalin was a slightly less effective branching agent than Maxcel, conversely, Promalin stimulated leader growth rate resulting in improved final tree height. Maxcel reduced leader growth rate and final tree height slightly but gave the widest branch angles. Multiple sprays of Gibberellins 4+7 applied to nursery trees in the late summer inhibited flower bud development and flowering in the orchard the next year. This reduces the risk of fire blight in newly planted trees. Maxcel effectively induced lateral branching in the orchard in years 1 and 2 when developing a new Tall Spindle orchard. We suggest 15 days after bud break and 500–1000 ppm.