Ministry of Agriculture & Lands
Tree Fruit Leader, Vol. 5(1) April 1996
Pruning and Thinning Fuji
by Mike Sanders, Tree Fruit Specialist, BCMAFF, Kelowna
Mr. Hiromitsu Komatsu was one of the featured speakers at the International Dwarf Fruit Tree Association annual meeting held in Penticton from February 25 to 29,1996. Following this, he gave two orchard discussions to Okanagan growers on pruning and thinning Fuji for fruit size, fruit quality and annual production.
The following is my summary of these sessions plus comments made individually as we travelled and visited.
The Japanese use pruning and thinning techniques that encourage production of large, high quality fruit on an annual basis. This is not easy, as Fuji can be very biennial. In the case of Fuji there is a connection between pruning and thinning in regards to annual production.
In the Nagano area of Japan, new Fuji plantings are usually on MaIling 9 or MaIling 26 rootstocks. Trees are trained to a system very similar to vertical axis. Spacing ranges from 13' x 5' (670 t/a) to 16' x 10' (272 t/a). Tree height extends to about 12 feet.
Slender spindle training has been tried in Japan. This system, however, was found to be unsuitable for the production of quality fruit because of the Fuji growth habit.
Fuji is more vigorous than other varieties and because of coloring problems, requires careful management of nitrogen and wider spacing to allow for adequate light distribution. Because of vigorous growth and drooping growth habit, light pruning is the rule. Trees are never headed except when a terminal flower bud is removed to develop a renewal shoot.
In the early years Fuji are pruned lightly to encourage early production. At planting, whips are headed at 33" to 39" (85 to 100 cm). This is the last heading cut that most trees will receive. Nothing is done during the first growing season although I suspect some pinching of the second, third and perhaps the fourth shoot below the heading cut would be beneficial.
In the second spring, only strong and narrow branched shoots which compete with the leader are thinned out. All shoots are trained to the horizontal and left unheaded. Training to the horizontal helps to reduce blind wood which can be a big problem.
In the third, and subsequent years, shoots near the leader are thinned and trained in the same manner as in the second year.
After the fourth year, the lowest branches are gradually thinned and 3 or 4 remaining branches are left at the 3 to 5 foot height as permanent branches. Higher than normal basal branches are necessary as Fuji has a drooping growth habit. Excessive shoots and branches causing shade in the upper part of the tree are removed each dormant season. Trees are kept to a conical shape. At maturity trees will have from 15 to 20 branches with only the basal branches being permanent. Weak and excessively drooping branches (pointing almost straight down) and leaders are thinned back to more upright shoots or branches.
Understanding the flowering and fruiting habit of Fuji is very important for both fruit quality and annual production.
Fuji flowers on spurs on 2 year old and older wood, from terminal buds on 1 year old shoots and dards and from lateral buds on 1 year old wood. The preferred fruiting wood is terminal fruit buds from shoots 1/2 inch long to 6 inches long, terminal fruit buds at the ends of branches and spurs on 2 year and older wood. Fruit from lateral buds on 1 year old wood is never used in Japan.
During dormant pruning fruiting wood not meeting requirements (shoots and dards longer than 6") is removed flush to the branch. I have seen some growers leave a stub for renewal growth.
Removal of some of this wood does not always seem necessary but it serves two useful purposes. The first is that it gets rid of fruit buds that normally do not produce the best fruit and secondly, it thins out the crop before bloom which helps in reducing biennial bearing.
Pruning in the dormant season is only a small part of the Fuji thinning program to keep trees producing annually.
Japanese growers thin by hand and with chemicals but on a stricter basis than we are used to.
The hand thinning program has three distinct stages.
The first stage starts when the lateral fruit buds on 1 year old wood are at the pink stage. All the lateral flowers are removed.
The second hand thinning starts at bloom and is finished within 30 days of bloom. All side blossoms or fruit from terminal buds are removed. If the king blossom or fruit is damaged, the largest side blossom or fruit, is retained.
The final hand thinning is finished by 60 days from full bloom. This thinning balances the crop load to attain maximum size, quality and return bloom.
Growers in Nagano leave 1 fruit for each 4 to 5 fruiting terminals. These are spaced out along the branch. Mr. Komatsu feels that we should experiment with leaving 1 fruit for each 2 to 3 fruiting terminals as size may not be as important for us as it is for them. Regardless, we should not leave more than 1 fruit for each 50 leaves on the tree as biennial bearing tendency will increase and quality may decrease.
It is important that this final hand thinning be finished within 60 days of blossom for Fuji to have any chance of coming back with a crop the following year. Keep in mind that much of the Fuji crop is borne on terminal buds of one year wood so fruit bud initiation will probably not start until late June or early July. It may also be advisable to have this thinning done earlier to give maximum opportunity of having return bloom.
My impression is that usually only growers with small holdings follow this hand thinning procedure.
I would be very surprised if any British Columbia grower attempted to thin Fuji by hand. I reviewed the process, however, to show the importance of timing as this is very important when thinning with chemicals.
Larger growers in Japan do chemically thin. They use blossom materials and Sevin. The materials are directed at specific blossoms or fruit so timing is critical.
Again, remember that a good portion of the crop comes from terminal fruit buds. These buds, and spurs on 2 year and older wood will be the first to flower in the spring and the king blooms will open ahead of the side blooms. The last to open will be the lateral flower buds on 1 year wood which produces the poorest quality fruit.
The blossom thinner used is lime-sulphur. It is directed at lateral flower buds. By doing this, the king bloom and perhaps some side blooms of the terminal fruit buds are usually set so the spray will not affect them. By applying one or two lime-sulphur sprays at the right timing many, if not all, of the fruit from lateral blossoms may be eliminated.
We would not use lime-sulphur as it would interfere with our integrated pest management program. We do, however, use ATS (ammonium thiosulphate) near the blossom period and at 1.6 litre/l00 litre of water we might get some good thinning.
The next thinning material applied is Sevin. It is used much as we use it and is directed at the side blooms of the terminal fruit buds. It is used when the largest fruit reach 10 to 12 mm in diameter. I cannot comment on earlier applications on Fuji but hope to try some this year.
As we have found with our thinning programs, it is very unlikely that enough fruit is removed. Some hand thinning, therefore, is necessary and this is done as soon as possible to influence return bloom.
When grown well in a suitable climate Fuji is a very fine apple. So far, we have not shown that we can consistently produce a good quality Fuji on an annual basis. The Japanese approach to pruning and thinning Fuji makes a lot of sense and is definitely worth trying.
