Foliar Calcium Applications Do Not Improve Quality or Shelf Life of Strawberry, Raspberry, Blackberry, or Blueberry Fruit

Abstract

Foliar calcium (Ca) products are applied by many berry growers to enhance fruit quality and shelf life without evidence that these applications increase fruit Ca or impact fruit characteristics when applied at rates recommended on the product label. The objectives of this study were to determine if fruit or leaf Ca increases when several formulations of liquid Ca products are applied to developing fruit, and to assess any resulting changes in fresh market quality of berries. Products were applied in strawberry (Fragaria ×ananassa L., ‘Hood’ and ‘Albion’), raspberry (Rubus idaeus L., ‘Tulameen’ and ‘Vintage’), blackberry (Rubus L. subgenus Rubus, Watson, ‘Obsidian’ and ‘Triple Crown’), and blueberry (Vaccinium corymbosum L., ‘Spartan’, ‘Liberty’, ‘Draper’, and ‘Legacy’). Calcium formulations tested were Ca chloride (CaCl2), CaCl2 + boron, Ca silicate, Ca chelate, and Ca acetate, which were compared with a water-only control. The rates used for each product were within ranges specified on the label and supplied equal amounts of Ca per ha for each treatment; the Ca concentration varied from 0.05% to 0.3% depending on the cultivar and the volume of water required for good coverage. All products were applied with a backpack sprayer, except in a separate trial where a backpack and electrostatic sprayer were compared in ‘Draper’ and ‘Legacy’. Treatment applications were started at the early green fruit stage and were repeated three or four times, depending on duration of berry development and cultivar. Fruit were harvested into commercial clamshells 4 days to ≈4 weeks after the final application of Ca from an early harvest at commercial ripeness. Data collected included berry weight, rating of fruit appearance and flavor, firmness, skin toughness, total soluble solids (TSS), and weight loss and nesting (collapse of fruit) during storage (evaluated at ≈5-, 10-, 15-, and 20-days postharvest). Fruit and leaves were sampled at harvest to determine Ca concentration. There was no evidence of spotting or off-flavors due to Ca applications. Compared with the control, none of the Ca treatments or method of application changed leaf or fruit Ca concentration, fruit quality, firmness, or shelf life in any crop or cultivar tested.