Influence of ReTain and NAA On Preharvest Drop, Fruit Quality and Storage Potential of ‘Mcintosh' Apples

Recently it has been reported that the addition of naphthaleneacetic acid (NAA) to  preharvest drop control applications of AVG (ReTain) improved fruit drop control.  McIntosh is one of the most drop prone commercial varieties grown.  Use of NAA as the sole drop control strategy on this cultivar is generally not done because it can advance ripening and shorten postharvest storage life.  This investigation was initiated to examine the effect of combination sprays of NAA and ReTain may have on preharvest drop control, ripening and storage potential.  ReTain was applied at a full commercial rate (333 g/acre) or 3 half rates applied at 2-week intervals.  NAA at 10 or 20 ppm was applied one, two or three times with the full or half rates of ReTain.  The addition of NAA one or two times at either concentration to the full rate of ReTain resulted in improved drop control compared with just ReTain alone.  The addition of NAA at 10 ppm with the three half rates of ReTain resulted I slightly better drop control than three applications of ReTain alone.  Whereas three applications of 20 ppm NAA with three half rates ReTain was the poorest drop control treatment and this combination also resulted in some advancement of fruit ripening. The addition of NAA to ReTain in general did not hasten fruit softening nor did it have any influence on flesh firmness after 6 or 12 weeks of regular air storage.  It is concluded that ReTain is able to negate symptoms of ripening when moderate rates of both compounds are used.  It is a good strategy to include a moderate rate of NAA with ReTain in a preharvest drop control program for McIntosh.