Cultural manipulation for out-of-season peach production under glass

Abstract

Low-chill peach cultivars grown under glass were forced to flower and fruit several months before the open orchard situation by cultural manipulation. Five chemical budburst treatments were tested: hydrogen cyanamide, potassium nitrate (KNO 3), thiourea, dinitro compounds (DNC), and DNC followed 7 days later by a mix of KNO 3 and thiourea. None improved budburst beyond that of the control and all but KNO 3 had a phytotoxic effect. Zinc sulphate was ineffective as a chemical defoliant. Hand defoliation was successful in forcing budburst. Defoliation in February (late summer) and March (early autumn) forced a few flowers of which many abscissed prior to anthesis or exhibited gross abnormalities. Abnormalities of the ovules, studied microscopically, included the absence of an embryo sac and, in some cases, a nucellus. Delaying defoliation until June (early winter) increased the number of flowers reaching anthesis, reduced the proportion of abnormal flowers and resulted in higher fruit yields. Vigorous vegetative growth was controlled with PP333 applied as a soil drench in January (summer). Treated trees produced twice as many flowers as the controls, a high proportion of which had twin pistils, both of which set and matured. This increased the need for thinning, but still resulted in an economic yield.