Many traditional European cider cultivars are known to have biennial bearing tendencies and growers have reported that conventional thinners such as 1-naphthaleneacetic acid (NAA) and 6-benzylaminopurine (6-BA) are ineffective. The goal of this two-year study is to determine the efficacy of plant growth regulators (PGRs) on traditional European cider cultivars in reducing biennial bearing and improving juice and cider quality, while also maintaining sufficient yield to ensure profitability. The chemical thinners used in this study were applied with a backpack sprayer and consisted of the lowest and highest labelled rates of NAA (PoMaxa; Valent BioSciences LLC, Libertyville, IL) and 6-BA (MaxCel; Valent BioSciences LLC, Libertyville, IL) mixed with 1-naphthyl methylcarbamate (Carbaryl; Sevin SL; Loveland Products Inc, Greeley, CO). The chemical thinners were applied to the high-tannin cider cultivars, ‘Binet Rouge’, ‘Chisel Jersey’, ‘Dabinett’, ‘Harry Masters Jersey’, and ‘Porter’s Perfection’. The experiment was conducted at the Cornell research orchards in Ithaca and Lansing, NY, as well as commercial orchards in Walden, Lyndonville, and Trumansburg, NY. Each site was a fully replicated (n = 5) randomized complete block design. Preliminary data found that chemical thinning reduced crop load between 24% and 62% (measured as the total number of fruit per tree) and increased individual fruit weight (measured in grams) between 24% and 70%. Additionally, chemical thinning increased soluble solids concentration in the juice (measured in degrees Brix) between 6% and 29% and increased titratable acidity (measured in grams/liter) between 9% and 29%. These results demonstrate that PGRs can be effectively used to manage crop load for European cider cultivars. A second field season is planned for 2025.
