Tree Fruit Leader, Vol. 2(1) Feb. 1993

Increasing fruit size of Royal Gala

The following article is re-printed from Fruit Notes, Spring 1992, Vol. 57, Number 2, prepared by Department of Plant and Soil Sciences; University of Massachusetts Cooperative Extension System, US Department of Agriculture, and Massachusetts Counties Cooperating.

by Duane W. Greene, Wesley R. Autio, Joseph Sincuk, James Krupa, and William J. Lord. Department of Plant and Soil Sciences, University of Massachusetts

Gala has rapidly risen in popularity to the point where it is now one of the most heavily planted apple cultivars in the world. It has many desirable attributes including very high quality, attractive appearance, precocity, and high production. One of the major faults of this cultivar is small fruit size. While prices in the market for Gala generally are high, a premium is paid for large fruit. We initiated several studies specifically intended to investigate conditions that may influence the size of Gala, with the goal of identifying practices which may increase Gala size.

Type of fruiting wood

It was suggested (American Fruit Grower 109(4):42-44, 1989) that the largest Gala apples are borne terminally on short shoots (3 to 10 inches), that the smallest are produced on one-year-old wood, and that those of intermediate size are found on spurs of two-year-old wood. We selected 29 five-year-old Royal Gala/M.26 trees, and at normal harvest, we harvested from each tree lateral fruit on one-year-old wood, terminal fruit on shoots 6 to 10 inches long, and fruit located on two-year-old spurs. Fruit from each tree were weighed and the diameters were measured. Fruit located on one-year-old wood were significantly smaller than those on other types of wood (Table 1), a relationship that is common in most apple cultivars. Fruit located terminally on short shoots was of comparable weight and diameter to fruit located on two-year-old spurs.

Table 1. Relationship of fruit location on the tree and size at harvest of Royal Gala apples

Gala normally produce some short shoots; however, based on this study, there does not appear to be a good reason to increase artificially the number of short shoots on Gala, since fruit borne on these shoots were no larger than fruit on spurs. Efforts should be made, however, to reduce the number of fruit on one-year-old wood, since fruit size on this wood was significantly smaller. Fruit borne on the tips of branches weigh down the branches, reducing growth and light penetration into the interior of the tree and lower branches. Fruit on one-year-old wood ultimately reduce fruit quality and devitalize fruiting spurs and short shoots. Strategies should be developed to remove fruit on one-year-old wood selectively.

Distribution of flowering and fruit set on Royal Gala

If the location of fruit influences fruit size, then it is important to know the normal flowering habit and fruit set distribution of Gala. Royal Gala/M.26 planted in 1988 were used in this study. In 1990, two branches per tree were tagged and measured at bloom, and all of the flowers on spurs and one-year-old wood were counted. In 1991, bloom was determined similarly but fruit set was also taken. Over two thirds of all flowers on Royal Gala were produced on one-year-old wood (Table 2). The location of flowers was strikingly similar in the two years.

Table 2. Bloom and fruit distribution on Royal Gala apple trees

Fruit set was heavy in 1991. Although the percent of flowers that set on one-year-old wood was lower than that on spurs, following June drop these fruit still represented nearly two thirds of all of the fruit that set on these limbs.

For most cultivars the majority of flowers are borne on spurs or terminally on short shoots. On these cultivars, bloom on one-year-old wood can vary significantly, depending upon the year, but typically it does not constitute the majority of the flowers on a tree. Gala is different in that most of the flowering does occur as lateral bloom on one-year-old wood and this lateral bloom sets significant numbers of fruit. Bloom data presented here for Royal Gala were part of a larger Gala strain trial. Bloom was determined similarly on the other four strains included in this trial. The distribution of bloom and fruit set was similar for all strains. Therefore, the abnormally large amount of lateral bloom and high fruit set of these lateral fruit is typical for standard Gala and several of its red coloring strains.

Thinning treatments to increase fruit size

Adequate chemical thinning is a key component 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 estalish 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 SevinTM, 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 random from each tree and then weighed.

Trees that were not chemically thinned set a heavy crop with small fruit size (Table 3). Significant 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 experiment, 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 treatment was 2.9 inches.

Table 3. Effects of postbloom thinning treatments on fruit set and size of Royal Gala apples.

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 increase 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 converted 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 probably 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 reported 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 cultivars. 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 appropriate.

Conclusions

Most flowers on Gala are produced on one-year-old wood, and a significant number of these set fruit. Since these fruit are small and their presence influences tree structure and the quality of other fruit on the tree, a special effort should be made to remove these early in the season. A combination of Sevin and 3 ppm NAA was considered the most appropriate chemical thinning treatment on Royal Gala in 1991. Once fruit have reached proper maturity, Gala should not be allowed to remain on the tree to obtain additional size. Trees should be pruned to allow good light penetration and assure continued development of new fruiting wood.

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