Some uses of plant growth regulators in modern apple production systems

March 2012 | Prepared and presented by Steven J. McArtney, North Carolina State University | Future Orchards® Orchard Walk notes and presentation

Steven McArtney explains how plant growth regulators (PGRs) can be used across modern apple production, focusing on crop-load management, russet control, return bloom and pre-harvest fruit drop. The resource links PGR performance to plant physiology, particularly carbohydrate supply, fruit growth, ethylene and flower-bud initiation.

A major section explores why chemical thinning response changes with weather. Low light and high night temperatures can create carbohydrate deficits, and the MaluSim carbon-balance model is presented as a way to anticipate whether standard thinner rates are likely to be weak, normal, aggressive or potentially excessive. McArtney also describes how reduced fruit-growth rate in the week after a thinner application can help predict which fruitlets will abscise.

The notes also cover summer NAA and Ethrel programs to promote return bloom in biennial-bearing cultivars, and the use of ReTain® and NAA for pre-harvest drop management. The central message is that PGRs are not “silver bullets”: reliable results depend on timing, weather, cultivar, crop load, tree vigour and correct interpretation of the biological process being manipulated.