COMPARISON OF NAA AND SEVIN PETAL FALL SPRAYS ON FRUIT SET OF APPLES

Abstract

In Washington and other western states Elgetol, a blossom thinning agent was previously used before the postbloom NAA and Sevin applications and there was no need for an earlier timing of NAA and Sevin treatments. In 1989, Elgetol was removed from the market by the manufacturer because of minor crop use and the high cost of re-registration. Without a blossom thinner it is impossible to guarantee a return bloom on severe biennial bearing cultivars such as Golden Delicious and Fuji. Even though adequate fruit thinning occurs with the postbloom thinning sprays, flower Initiation may not occur for the next years crop because the application is made too late.NAA and Sevin are used as postbloom sprays for reducing fruit set of apples. The usual time of application is when the largest fruit are from 10 to 15 mm in diameter. Sprays applied at the 10-15 mm fruit diameter stage take advantage of warm weather after spraying which increases stress and maximizes reduction of fruit set with a minimum effect on the seed number, however, when temperature is cold seed abortion occurs without adequate reduction of fruit set.This report compares the efficacy of the postbloom thinners NAA and Sevin as early petal fall sprays for reducing fruit number and increasing return bloom the following year. Sevin is most effective as an apple fruit abscission agent when applied at petal fall. In trials for 2 years there was no reduction in fruit seed number, no reduction in fruit size and no effect on fruit shape. In comparison NAA applied at petal fall tended to reduce seed number, reduce fruit size, flatten or distort fruit shape and cause leaf curling.