Reduction of red colour in Starkrimson apples using calcium nitrate sprays

Abstract

Experiments were conducted for two years in Southern Tasmania on Starkrimson apple trees in an attempt to lighten the unacceptable dark red colour of the fruit. Treatments consisted of spraying trees with zero (control), two, four, six and eight sprays of 0.5% w/w calcium nitrate. Sprays were applied at weekly intervals, each treatment being completed one week prior to a common harvest date. In both years calcium nitrate reduced red colouration, the magnitude of the reduction was dependent on the number of sprays. In 1976 the proportion of unacceptable apples was reduced from 40% to 13% by eight sprays of calcium nitrate. The proportion of unacceptable fruit was further reduced from 13% to 1% during cold storage and ripening. Colour did not develop strongly in 1977 and although the effects of calcium nitrate sprays and storage plus ripening were to reduce red colour they were of no practical significance. A further experiment in 1977 tested the effect of increasing the concentration of calcium nitrate from 0.5% to 1.0% and 1.5% w/w, in an effort to reduce the number of sprays. No significant colour reduction resulted from these treatments. Yield was not significantly affected by any treatment. Calcium nitrate sprays reduced the incidence of breakdown in the 1976 trials at the higher number of applications, but no difference was detected in 1977.