The only other drop-controlling chemical that is reg- 

 istered for use on apples is naphthaleneacetic acid (NAA). 

 If growers in Massachusetts must depend on this com- 

 pound, then a reevaluation of its effectiveness is necessary, 

 since most of the research on NAA was done prior to 1960. 

 Pruning and training systems, pest control programs, root- 

 stocks, orchard management practices, and fruit condition 

 requirements have all undergone significant changes since 

 that time. 



A study was initiated in 1987 to answer several specific 

 drop control questions: 1. How effective is NAA at 

 controlling preharvest drop of Mcintosh? 2. How long 

 does drop control from NAA last? 3. Can growers first spot 

 pick then effectively control drop with NAA? 4. How much 

 drop occurs as a result of harvesting? 



A block of 11-year-old Rogers Mclntosh/M.26 were 

 selected and divided into 8 groups of 8 trees each. Two 

 trees in each group were sprayed with 750 ppm Alar (2.25 

 lbs per acre) on July 17, 1987. When the first sound fruit 

 began to drop on September 8, NAA at 10 and 20 ppm was 

 applied to a tree in each group. This timing is recom- 

 mended on the NAA label. It was decided that September 



14 was the day that a commercial grower would begin spot 

 picking these trees. All fruit that had sufficient color to 

 meet the U. S. Extra Fancy grade were harvested from half 

 of the trees in each block. On September 15 NAA at 10 or 

 20 ppm was applied to a portion of the trees that were 

 previously spot picked. Drops were removed from under 

 trees prior to and immediately after spot picking. All drops 

 were removed 3 to 4 times weekly from September 1 to 

 October 2 and then twice weekly until the experiment 

 ended on October 20. 



The NAA label recommends that application should 

 begin as soon as the first sound, uninjured fruit begin to 

 drop. This timing occurred on September 8. Whenapphed 

 at this time 10 ppm NAA was as effective as Alar at 

 controlling drop for 8 days, and 20 ppm NAA was as 

 effective as Alar for 10 days (Figure 1). After 10 days Alar 

 was clearly the superior drop controlling chemical. Cumu- 

 lative drop on trees receiving NAA was significantly less 

 than on control trees, even as long as 6 weeks after 

 application. Although fruit quality was not evaluated in this 

 experiment, it was noticed that fruit receiving NAA were 

 noticeably softer and riper at the end of September. 



Cumulative drop (%) 



100 



80 



60 



40 



20 



I I I I I I I I 



Sept 2 



Sept 1 1 



I I I I I I I I I I I I I I I I I I I I I I I I I I 



Sept 20 



Sept 29 



Gets 



Oct 17 



Figure 2. Cumulative drop after spot picking on September 14 from trees which received 

 Alar, NAA (10 or 20 ppm on September 15), or no drop-controlling treatment. 



13 



