Thinning Peaches by Heat

Abstract

Flower buds in their last stages prior to opening, open flowers and small fruitlets are the most sensitive organs to frost damage. Such effect of low temperature is well-known as it poses an economical hazard in growing stone fruits in many countries. Heat effect on flower buds and flowers is less known simply because it is not common at time of bloom in most locations where such species are grown. Many of the low-chill early maturing peaches and nectarines set very heavily in subtropical climate and require a major input of manual thinning in order to obtain marketable fruit. As the level of fruitset is usually very high, thinning is been carried out during full bloom. With increase in costs of manual labor, this element becomes the critical one in producing such fruits economically. Up till now, no chemical or physical mean can replace hand-thinning in these early cultivars effectively. During our work with greenhouse-grown stone fruits we came across the enormous sensitivity of non-dormant flower buds as well as flowers to high temperatures. Avoiding excessive heat close to, and during bloom, became number one concern in the practice of growing stone fruits in greenhouses. By using container-grown peaches and temperature-controlled chambers in a phytotron, we were able to quantify the effect of heat on flower buds with the potential of obtaining controlled damage leading to the required level of thinning. Trials with potted and with orchard grown trees will be reported.