Preharvest Drop Control Suggestions for McIntosh for 2014
The time for preharvest drop control application will soon be here. In an attached article we summarize results from preharvest drop control studies done over the past 5 years. Based upon these studies we are making recommendations for this coming season. The major goal in these studies was to come up with a strategy to extend acceptable drop control to the Columbus Day weekend. In situations where drop control is not required as late as the Columbus Day weekend, less ReTain will be required.
We selected a base time of application of 3 weeks before the start of anticipated harvest which this is consistent with label directions. Applying the first ReTain application at this time achieved reasonable drop control while having a reduced effect on delay in red color development. An application of one pouch (333g) per acre generally resulted in drop control (less than 20% drop) for between 34 and 40 days. If additional drop control is desired then additional amounts of ReTain will be required. In previous studies an additional ½ pouch of ReTain per acre applied 2 weeks after the first ReTain application provided some additional drop control. In 2013 applying a full pouch of ReTain per acre 2 weeks after the first full pouch resulted in excellent drop control with less than 20% drop through the Columbus Day weekend.
Does the addition of NAA help when applied with ReTain? In the 4 years when NAA was included with the base rate of ReTain applied 3 weeks before anticipated harvest, it extended drop control in only one year. The reason for this is unclear. In all 5 years when NAA was included in some combination with ReTain as a drop control agent it did not advance ripening unless too little ReTain was used. In general, one pouch of ReTain per acre with 10 ppm NAA resulted in no advanced ripening. However, if the amount of ReTain applied with NAA was below ½ pouch per acre advanced ripening did occur.
Base recommendation for 2014. Apply one pouch of ReTain per acre 3 weeks before anticipated harvest. Follow this application with ½ pouch per acre 2 weeks later. This should provide drop control through September. If retardation of ripening is desired an earlier application will be necessary. If longer drop control is desired increase the amount of ReTain to 1 pouch per acre 2 weeks after the first application. The ReTain label restricts application to no more than 1 pouch per acre per time of application. In formulating your own strategy 2 rules-of-thumb are useful. First, the more ReTain you apply the better (longer) the drop control. This is a linear response. Second, the earlier the application the greater the retardation in fruit ripening you can expect.