Effect of particle film on fruit sunburn, maturity and quality of 'Fuji' and 'Honeycrisp' apples

Studies were initiated to evaluate the effects of a kaolin clay particle film product on fruit sunburn, size, color and maturity of 'Fuji' and 'Honeycrisp' apples and fruit mineral concentration of 'Fuji'. Trees in both studies were sprayed with kaolin clay (Surround(TM), Engelhard Corp., Iselin, N.J.) at the rate of 56 kg (.) 1870 L-1, applied with an air-blast sprayer calibrated to apply 1870 L (.) ha(-1). In Idaho, six-year-old 'Fuji' apple trees on M.26 EMLA and B.118 rootstocks were sprayed with kaolin clay on 10, 17, and 24 July 2000. In New York, six-year-old 'Honeycrisp'/M.26 EMLA apple trees were treated as follows: 1) untreated control; 2) kaolin particle film applied weekly from 15 May to 26 June; 3) kaolin particle film applied weekly from 6 July to 17 Aug. Kaolin particle film reduced fruit weight, red color, and the incidence of sunburn of 'Fuji' apples in Idaho. Sunburn did not occur on 'Honeycrisp' in the New York study. In that study, kaolin particle film had no effect on fruit weight or red fruit color when applied in May and June but reduced fruit weight and red color when applied later. Applications of kaolin particle film in July and August (New York) reduced both the proportion of the skin surface that was red, and also the red hue on the blushed portion of the skin. The reduction in red color development observed in 'Fuji' and 'Honeycrisp' was not related to a change in mineral nutrient concentration or to a delay in fruit maturity. Reductions in fruit color and size in our study are possibly due to an increase in the amount of reflected light, resulting in light-limited carbon fixation and color development. Based on our results, growers who choose to use kaolin particle film sprays to reduce sunburn should recognize that applications later than June may reduce red fruit color of apples and result in smaller fruit.