After the Freeze – Damage Mitigation Possibilities

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Henderson County apple growers experienced another round of freezing temperatures early Thursday morning (April 22) and another round could be in store for tomorrow morning (April 23). Coming on the heels of the freezes over Easter weekend, this could create a situation of additive losses for some growers that experienced significant bud mortality in the first event.
NEWA weather stations around the county and reports from growers indicate that low temperatures ranged from as low as 25°F to 31°F in the early morning hours.
Benzyladenine and gibberellic acid in for formulation of GA4+7 and 6-BA has been shown to help mitigate damage from froist/freeze events. This material is sold under the tradenames Promalin and Perlan. The label covers only the bloom period. Unless in the bloom period, you should not use this material for frost rescue.
Since frost/freeze events are sporadic/unpredictable, there has been limited research related to use of Promalin for frost rescue. Following a series of frost events in 2012 during the bloom period McArtney et al. (2014) demonstrated an increase in fruit set and yield in some cultivars when using Promalin. This was true with applications up to 5-6 days following the freeze event in this study. See data from that study below.
Effects of gibberellin A4 + A7 and 6-benzyladenine (GA4+7 plus 6-BA) treatments after freezes during full bloom on 12 and 13 Apr. 2012 on fruit set, total yield, fruit number per tree, and mean fruit weight of ‘Taylor Spur Rome’/‘M.7’ apple in Henderson County, NC.
Treatment chart
Effects of gibberellin A4 + A7 and 6-benzyladenine (GA4+7 plus 6-BA) treatments after freezes during full bloom on 12 and 13 Apr. 2012 on marketable yield and cull fruit of ‘Taylor Spur Rome’/‘M.7’ apple in Henderson County, NC.
Treatment chart
While significant increases in yield were observed with some cultivars/locations with Promalin, this equated to approximately 25% of a full crop. For some operations, 25% of a crop would be an important source of revenue in a potentially difficult year. For others, this would result in an expensive and cosmetically flawed nuisance crop.
Promalin mimics chemical signals that are present in seeds, which can result in parthenocarpic (seedless) fruit development despite death of the embryo. Parthenocarpic fruit will have poor storage potential and may be misshapen. Subleathal injury to fruit (russet, frost rings, etc.) may be present. Your specific situation (site, temperature observed, market, crop insurance, etc.) should be considered before employing this rescue treatment. This is not “one size fits all”.
Those that are interested should refer to page 83 of the 2021 Integrated Orchard Management Guide for Commercial Apples in the Southeast for application information. Please follow label directions.