Foliar Applied Strontium as a Tracer for Calcium Transport in Apple Trees

in HortScience
Authors:
Carl Rosen*Univ. of Minnesota, Dept. of Soil, Water, & Climate, St. Paul, MN 55108

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Peter BiermanUniv. of Minnesota, Dept. of Soil, Water, & Climate, St. Paul, MN 55108

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Adriana TeliasUniv. of Minnesota, Dept. of Horticulural Science, St. Paul, MN 55108

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Yizhen ShenUniv. of Minnesota, Dept. of Soil, Water, & Climate, St. Paul, MN 55108

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Emily HooverfUniv. of Minnesota, Dept. of Horticultural Science, St. Paul, MN 55108

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A field experiment was conducted at the Horticultural Research Center in Chanhassen, Minn. to help refine recommendations for use of calcium (Ca) sprays to reduce the incidence of bitter pit in `Honeycrisp' apple. Specific objectives were to: evaluate the amount of translocation from leaves to fruit using strontium (Sr) as a tracer for potential Ca movement, determine whether there are differences in translocation in early vs. later phases of fruit development, and evaluate the effect of an experimental adjuvant on spray efficacy. Seven treatments tested included the following: 1) Control (no Sr applied), 2) Sr without adjuvant, fruit covered during spray application, full season, 3) Sr without adjuvant, fruit uncovered during spray application, full season, 4) Sr + adjuvant, fruit covered during spray application, full season, 5) Sr + adjuvant, fruit uncovered during spray application, 6) Sr + adjuvant, fruit covered during spray application, late season, 7) Sr + adjuvant, fruit uncovered during spray application, late season. Results from this study strongly suggest that Sr is a suitable tracer for foliar applied Ca. Up to 18% of the Sr applied to leaves was translocated to fruit. Eight full season spray applications more than doubled the concentration and content of fruit Sr compared to four late season sprays. The experimental adjuvant was found to double Sr absorption by and translocation to fruit compared to not using an adjuvant. Implications for foliar application of Ca to apple trees will be discussed.

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