Tree Fruit Leader, Vol. 5(2) Nov. 1996

Summary - Symposium on Enhanced Performance of Orchard Systems Through Knowledge of Canopy and Rootstock Physiology 

by Mike Sanders, Tree Fruit Specialist BCMAFF, Kelowna 

This International Society for Horticulture Science symposium was held in Wenatchee and Penticton from July 17 to 25, 1996. This symposium covered a lot of ground and provided considerable useful information. The following summarizes information on apples considered to be the most applicable to the B.C. situation. 

Rootstocks 

MaIling 9 is still considered the most productive rootstock; there are various clones of M.9 that influence tree size and productivity; clone T 337 from Holland (the one mostly used in BC) is a good choice but several others are also suitable; 

B9, 03 and Jork 9 are all considered to be more winter hardy than MaIling 9 and are productive; 

In Australia 03 has performed very well with Gala and matures the crop sooner; stem grooving virus of 03 seems to be a concern with Fuji; and 

Several Cornell-Geneva rootstocks from New York are in the process of being released; there doesn't seem to be any advantages over what is presently being used. 

Environmental Physiology: 

Corelli - Grappadelli of Bologna, Italy, mentioned that they have direct light and as a result leaves and fruit either get full sunlight or full shade and nothing in between; this was a very interesting comment as we predominantly have direct light and I have always thought systems should be chosen with type of light in mind (i.e. thin canopies for direct light conditions); 

New Zealand apparently has the highest yields in the world; a study tried to determine why this is the case but the results were not conclusive; it may be related to temperatures following harvest before leaf fall; Lakso of New York mentioned that roots never go fully dormant in New Zealand and this might be a factor influencing their large yields; 

The hierarchy of carbon sink flow (products of photosynthesis) is fruit, shoots, and roots; 

The more vigorous the rootstock, the higher the respiration; 

To increase photosynthesis (or to maintain) during the growing season: keep trees open and well lit; eliminate stress; when trees are shaded they lose their photosynthetic ability and even if opened up such leaves will not regain their photosynthetic potential; 

Growth regulators shut down vegetative growth so all products of respiration go to fruit and reproductive processes; 

Damaged leaves result in reduced photosynthesis; 

Tustin of New Zealand reported on effects of defoliation at different times after harvest - early defoliation resulted in less yield and size the following year; 

Lakso reported the major limitation to productivity is light interception; interception of light by spur leaves is important for the current season's crop and also for next year's crop; the most effect from shade occurs about 2 to 3 weeks from bloom; 

Apple leaves age rapidly in the shade and lose effectiveness; this helps explain why large volume, shaded trees are less yield efficient than small, open trees; the greatest risk of carbon deficiency is around 3 weeks from bloom; and, 

Type of cloud cover has a big impact on light levels: 

Orchard Systems 

Mika from Poland reported that super spindle was getting thick by year 4 and required 2 summer prunings; fruit size and quality was declining already in the fourth year; 

In experimental trials vertical axis looked best in Michigan and also in Norway; 

Perry from Michigan reported that a time study showed pneumatic pruners were twice as efficient as hand pruners; 

Widmer from Switzerland reported on the Mikado and Drilling training systems for apples and pears; both systems offer high production potential without the investments of super spindle densities; 

Costa of Italy discussed a trial with densities ranging from 2,778 to 9,524 trees per ha; as densities increased, trunk cross section area, fruit size and fruit quality all decreased; the best results after 4 years was 4,444 t/ha; 

Kim of Korea showed that on Fuji/M 26, thinning cuts resulted in more color and larger size than heading cuts; fruit is larger on more upright shoots but more fruit results from more horizontal shoots; 

Tustin of New Zealand reported on The International Apple Growth Study; sites are located at Kent (England), Cadriano (Italy), New Zealand and 6 locations in United States; this project started in 1986; New Zealand and Italy have most growth and Washington, surprisingly, the least; New Zealand has the largest yields and fruit size whereas England has the smallest fruit; 

Cheryl Hampson of Summerland Research Station presented a summary of the "fan" planting at the station; this interesting trial is testing five planting densities and three training systems using two varieties; fourth year results show that fruit color and size decreased at the highest densities and that fruit color was lower on Y-trellis than on short or tall spindles; 

Atkinson of East MaIling reported on root restriction of apple to restrict growth; tree size control did result but fruit size was also less; 

Ferree of Ohio showed that root pruning of apples resulted in smaller trees, smaller fruit and less yields regardless of rootstock; 

Naor from Israel researched various irrigation levels; for large fruits on heavy crop trees high rates of water are required; local experience indicates this may be especially so with dwarfing rootstock; key is to know how much water your trees need during the hottest part of the year and how much you are actually applying; and, 

The last "formal" presentations were by Rademacher and Winkler of BASF; they provided some very interesting information on BAS 125 W, a new growth regulator material that controls vegetative growth on apple and improves red color; it is expected to be available in the U.S. market

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