Results 



In general, ReTain affected fruit quality at harvest 

 predictably (Table 1). ReTain retarded red color 

 development but this reduction in red color was not 

 sufficiently great to consistently reduce the number of fruit 

 classified as US Extra Fancy. All ReTain treatments 

 retarded the loss of flesh firmness. No treatment influlenced 

 fruit soluble solids. Fruit maturity, as determined by starch 

 index, was retarded only when Silwet was included with the 

 ReTain. NAA advanced fruit maturity but otherwise had 

 little influence on other fruit quality. 



ReTain had little influence on red color development on 

 the first two harvests but at the later harvests red color 

 development was delayed (data not shown). Conversely, 

 ReTain retarded starch degradation at the early harvest 

 dates, but at later harvests the differences were less. 



All ReTain treatments retarded preharvest drop on 

 Marshall Mcintosh (Figure 1). However, during the last 

 week in September, the ReTain treatments containing 

 Kinetic or having no surfactant became clearly less effective 

 at controlling preharvest drop than the ReTain treatment 

 containing Silwet. The ReTain treatment containing Silwet 

 continued to be better than the other two ReTain treatments 

 for the duration of the experiment. NAA in general was 

 ineffective as a preharvest drop compound. Only once, on 

 September 15 (10 days after application), did NAA 

 significantly retard drop, and the reduction at this time was 

 only 4% better than the untreated control. 



Discussion 



The commercial harvest window of the fiuit based upon 



starch-iodine index was from mid to late-September (4.5 to 

 6 weeks after ReTain application). Application of ReTain 

 following label directions using 0.1% Silwet, a recom- 

 mended surfactant, effectively controlled preharvest drop. 

 Drop control of ReTain-treated fruit without a surfactant or 

 when applied with Kinetic was not as effective as when 

 Silwet was used. However, the differences in drop control 

 between these two treatments did not become apparent until 

 after most of the harvest would have been completed (5 

 weeks after ReTain application). 



Currently, there are four surfactants recommended for 

 use with ReTain: Silgard 309, Silwet L-77, Break-Thru, and 

 RNA Si 100. The latter two are only available through 

 suppliers located on the west coast. We suggest using only 

 the reconrmended surfactants, thus for growers on the east 

 coast the choice is limited to either Silwet L-77 or Silgard 

 309. 



ReTain had a small but significant effect on red color 

 development. We do not look at this as a reduction in red 

 color development per je, but rather a delay in development 

 that is associated with consequence of delayed ripening. 

 Fruit would have had similar if not greater red color if one 

 compared red color on fruit of a comparable starch rating. 



NAA has been registered as a stop-drop compound for 

 many years. However, its use on Mcintosh is not 

 widespread. Many years it is not effective or at best it is 

 marginally effective. In this investigation NAA had little 

 effect on drop control. Unless it can be made to work more 

 consistently, its use on Mcintosh is likely to be very limited. 

 NAA can advance ripening especially if warm weather 

 follows application. In this investigation weather \\as 

 seasonable, so ad\'anced ripening effects were limited to a 

 small increase in the starch index. 



ic i: i: it 'k 



36 



Fruit Notes. Volume 65. 2000 



