Thinning Treatments to 

 Increase Fruit Size 



Adequate chemical thinning is a key compo- 

 nent in getting good fruit size and consistent 

 crops. Because the popularity of Gala has risen 

 so rapidly, there are very few mature Gala trees. 

 Therefore, we have not been able to establish a 

 chemical thinning recommendation for trees 

 growing in the Northeast. A block of six-year-old 

 Gala/M.26 were selected in 1991 and divided 

 into 14 groups of four trees each. When fruit size 

 was 3/8 to 1/2 in, one tree in each block was 

 sprayed with either 1 lb per 100 gal Sevin™, 1 lb 

 per 100 gal Sevin plus 3 ppm NAA, or 1 lb per 100 

 gal Sevin plus 6 ppm NAA. One tree in each 

 group was not sprayed and served as a control. 

 The number of fruit persisting in July was 

 counted on two limbs per tree. At the normal 

 harvest time 40 apples were harvested at ran- 

 dom from each tree and then weighed. 



Trees that were not chemically thinned set a 

 heavy crop with small fruit size (Table 3). Sig- 

 nificant thinning occurred when Sevin alone 

 was used, although we do not believe that 

 enough fruit were removed. The addition of 

 NAA with the Sevin caused further thinning 

 which resulted in even larger fruit. Based upon 

 these data and observation of trees in this ex- 

 periment, we conclude that 1 lb per 100 gal of 

 Sevin plus 3 ppm NAA was the most appropriate 

 thinning treatment for trees in this block of 

 Royal Gala in 1991. We calculate that the 

 average fruit diameter of fruit from this treat- 

 ment was 2.9 inches. 



Influence of Time on Fruit Size 



It is generally believed that apple fruit 

 growth occurs at a relatively uniform rate 

 throughout the growing season. In the 60-day 

 period immediately before harvest fruit in- 

 crease in size by 0.8% to 1.0 % per day; however, 

 it was suggested (Fruit Varieties Journal 44:18- 

 22, 1990) that Gala may increase in size more 

 rapidly than other cultivars during the harvest 

 period. Ten fruit were tagged and the diameter 

 measured on eight Royal Gala trees in early 

 August and weekly for seven weeks. Fruit 

 diameter increase was curvilinear over the time 



measured. When the fruit diameter was con- 

 verted to fruit weight with a standard curve, 

 growth rate was linear. Over the 54 days that 

 the fruit were measured, fruit weight increased 

 at an average rate of 1.2% per day. While this 

 rate of growth is greater than in other published 

 reports, it is only marginally greater and prob- 

 ably not statistically higher. 



We do not believe that delaying harvest of 

 Gala is a viable way to achieve large fruit size. 

 Delaying harvest 10 days would produce a fruit 

 that weighs 12% more but the diameter would 

 increase by only 0.05 to 0.06 inches during that 

 period of time. There are also other factors to 

 consider. If left on the tree too long, Gala fruit 

 will crack, although, cracking has not been as 

 severe a problem in Massachusetts as it is re- 

 ported to be in other growing areas. In 1991, 

 Royal Gala were harvested on September 3, 12, 

 and 19. No cracking was noted on the first 

 harvest date, and only 1.1% of the fruit were 

 cracked at the two later dates. We estimate that 

 the optimum harvest date for Royal Gala on 

 these trees was September 15. Therefore, if fruit 

 are harvested at the proper time, very few fruit 

 will be cracked. When cracking does become a 

 problem, fruit maturity has advanced to the 

 point where the fruit feel 'greasy', and quality 

 has been diminished significantly. Gala has 

 been reported to require up to five harvests. If 

 trees are thinned properly and pruned to allow 

 good light exposure, we believe that Gala can be 

 picked in just two harvests. 



Pruning and Training 



Once Gala start to come into production they 

 can be pruned more severely than other culti- 

 vars. Gala flower and set fruit on more vigorous 

 and upright wood than most other cultivars. 

 Maintaining vigor in Gala assures production of 

 renewal spurs and sufficient spur leaf area and 

 shoot leaf area required for good fruit size. 

 Special efforts should be made to keep trees open 

 for good light penetration and to eliminate 

 weak, hanging wood that produces only small 

 inferior fruit and shades other areas of the tree. 

 Some summer pruning in August may be appro- 

 priate. 



Fruit Notes, Spring, 1992 



