The relation between weather and fruitfulness of the sultana vine

Abstract

The percentage of fruitful buds on sultanas is shown to be closely related to the weather over 3 weeks in late November and early December mdash; that is, during the period when the inflorescence primordia are differentiated. The two factors concerned are the hours of bright sunshine and the sum of daily maximum temperatures from 82 to 90°F. An estimate of the start of the period for which these weather elements are effective can be made by summing mean temperatures from bud burst. The study covers 18 years, 1945 to 1962 inclusive. Fruitfulness was lower than expected in the first 9 years, and higher in the second 9 years, possibly because of the use of Bordeaux spray in the first period and its replacement by organic sprays in the second. Fruitfulness can be forecast within practical confidence limits from a regression developed for fruitfulness from 1954 to 1962 inclusive on sunshine and maximum temperatures.