Comparison of Standard Calendar GA4+7 Plant Growth Regulator Programs to Applications Timed to Rainfall Events for Management of Scarf Skin, a Fruit Finish Disorder of Apple

Abstract

Scarf skin is a fruit finish disorder of apple that leads to reduced grade quality and rejected crop loads. Although not established as a disorder specific to certain cultivars, the manifestation of the disorder is more apparent on red-skinned cultivars such as Gala and Stayman at harvest, where its whiteish cast is held in clear contrast with the redness of the mature fruit. The disorder afflicts fruit during the first 40 days after petal fall as the fruitlet is developing, although symptoms of the disorder may not be clearly visible until many months after. The exact causes of apple scarf skin are not well defined, although it is known that the presence of the disorder can be influenced by environment, fruit size, and some pesticides. Management currently relies on four applications of the plant hormones gibberellins A4 and A7 (GA4+7) during the first 40 days after bloom. Here, we describe our attempts to use a commercialized GA4+7 product (ProVide 10SG) starting at petal fall, with applications made after or before rainfall events, to ease rainfall's putative influence on scarf skin development. We compared our programs to the standard program over 4 years in research orchards and a commercial orchard but observed no consistent reduction in scarf skin severity or incidence of out-of-grade fruit, in part due to the year-to-year variability in the manifestation of scarf skin. Rainfall, at the thresholds defined, does not appear to be a sufficiently significant factor influencing scarf skin development such that a GA4+7 management program can be designed. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .