Use of Plant Growth Regulators for Feathering and Flower Suppression of Apple Nursery Trees

in HortScience

The use of highly feathered trees can make high-density apple plantings more profitable through enhanced precocity and increased early yield. Currently, nurseries are asked to provide highly feathered trees with wide branch crotch angles. The use of plant growth regulators (PGRs) can play a key role when it comes to branch induction; however, dose and timing both need to be tested to enhance branching without compromising other tree quality attributes. Over the last 4 years, we have conducted studies of the use of MaxCel® (6-benzyladenine) and Promalin® (a mixture of 1.8% 6-benzyladenine and 1.8% GA4+7) in comparison with Tiberon™ SC (cyclanilide) at several nurseries in NY, WA, DE, Ontario (Canada), and Chile. The best results were obtained with four applications of MaxCel® or Promalin® (400 mg·L−1) beginning when leader growth reached 70 cm above the soil line and reapplied at 10–14 days intervals. Promalin® was a slightly less effective branching agent than MaxCel®. On the other hand, Promalin® stimulated leader growth resulting in improved final tree height, whereas MaxCel® induced the widest branch angles. Overall, we observed good response and quality ratings with ‘Cameo’, ‘Cripps Pink’, ‘Enterprise’, ‘Fuji’, ‘Ambrosia’, ‘Crimson Crisp’, ‘Gingergold’, and ‘Granny Smith’, whereas less quality ratings were observed on ‘Ambrosia’, ‘Cortland’, ‘Goldrush’, ‘Honeycrisp’, and ‘Suncrisp’. Response with ‘Gala’ varied depending on the temperature range. Multiple sprays of Gibberellins (GA4+7, or GA3) at 250 mg·L−1 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 infection in newly planted trees.

Contributor Notes

This research was partially supported by the International Fruit Tree Association, the Northwest Nursery Improvement Institute, the New Jersey State Horticultural Society, and the New Jersey Agricultural Experiment Station, with additional support from the Utah Agricultural Experiment Station (Journal paper #8959).

We thank John Baugher, Taun Beddes, Mike Beese, Shaun Calahan, Ricardo Chalhub Z., Gregory Clarke, Bill Howell, Dave Johnson, Wayne Kessinger, Bill Lawler, Rebecca Magron, and JD Obermiller for technical support and guidance. We also thank the cooperating nurseries Adams County, C&O, Univiveros, VanWell, and Willow Drive.

The authors have declared that no competing interests exist.

Corresponding author. E-mail:

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    Average daily maximum and minimum temperature (°C) and relative humidity (RH, %) for Santiago de Chile 2012 (Experiment 4), Quincy, WA, 2012–13 (Experiments 3 and 8), and Ellendale, DE, 2014 (Experiment 9). Bottom chart represents average daily minimum temperature (°C) for Geneva, NY, and Payson, UT, in 2014 (Experiment 11).

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    Effects of plant growth regulator treatments at 500, 750, 800, or 1000 mg·L−1 sprayed from two to five times (2× to 5×) on leader growth rate (cm per day) on ‘Fuji’, ‘Gala’, and ‘Granny Smith’ in the nursery at Chile in 2012 (Experiment 4). All the treatments included Regulaid® at 0.125% (v/v) as a surfactant. Vertical bars indicate least significant difference (LSD) at P < 0.05.

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    Effects of plant growth regulator treatments at 500, 750, 800, or 1000 mg·L−1 on number and length of feathers on ‘Fuji’, ‘Gala’, and ‘Granny Smith’ in the nursery at Chile in 2012 (Experiment 4). All the treatments included Regulaid® at 0.125% (v/v) as a surfactant. Vertical bars indicate least significant difference (LSD) at P < 0.05.

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    Effects of four or five applications of either MaxCel® or Promalin® on the overall tree quality of 17 apple varieties in Ellendale, DE, in 2014 and 2015 (Experiment 10). Tree quality (1 = poor, 5 = excellent) was subjectively assessed, taking into account overall tree height, number of feathers, and their angle. Excellent quality trees had a tree height of 180–200 cm and 12–15 wide-angle feathers, whereas poor quality trees were short in height and with no feathers at all. All the Promalin® applications included Regulaid® at 0.125% (v/v) as a surfactant. Bars with different letters denote significant differences among varieties (Tukey’s honestly significant difference, P ≤ 0.05).

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