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My Apples Didn’t Grow as Well as I Thought They Should Have – What Happened?

In spite of record heat accumulation, available soil moisture, adequate thinning and nutrition some apples didn’t grow the way they should have during the 2005 growing season. When we think of potential fruit size and manage our plantings for the best possible distribution of various sizes of fruit with an average of say 3”, some times we get the size and sometimes we don’t.

It is certainly easier if we start with a cultivar that is large fruited. Examples of small fruited cultivars include ‘Gala’, ‘Empire’ and ‘Chinook’. These varieties are inherently small and don’t have the type of genetics to easily produce large fruit size classes. Cultivars like ‘Crispin’, ‘Honeycrisp’ and ‘Cameo’, produce larger fruit by nature.

The practices of thinning and watering are probably the two most influential practices that a grower can use to influence average fruit size in any given block of fruit apart from adequate nutrition, including both macro nutrients and micronutrients.

Tree spacing and rootstock selection also come into play. A good cultivar starved of adequate light because of crowding or poor pruning practices will never reach expectations. Large fruit buds from adequate light interception is elemental in determining potential fruit size. This of course is directly related to pruning practices.

There are problems that can occur that take the vigour out of a tree and kill the nurturing capability of the foliage. Trees can get too much summer pruning and they can have the energy drained out of them by mite infestations and infections like mildew that essentially kill leaf performance. Without a healthy leaf canopy you cannot expect fruit to size to its best potential.

Last summer’s heat may have put more stress on trees than they needed. In trials where we compared trees with particle film on the crop and canopy versus untreated trees, we found that the particle film helped with fruit size on top of any benefits derived from good thinning and water management practices. Where measurements were made, treatments using particle film produced a distinctly larger and better finished fruit. These trials are part of our long term look at yellow skin cultivars (Golden Delicious types) with finish problems grown under Ontario growing conditions.

Invariably we do come across a crop that defies logic. For example, a perfectly healthy looking canopy and good management practices combined with a watering program and leaf to fruit ratios that are almost perfect producing fruit that are too small. See attached figure 2.

Figure 2 - Crispin apples showing very poor seed count.

When you get this combination of factors it’s best to check out seed count in the core of the fruit. More often than not, there will be too few seeds and/or too little weight to those seeds indicating a question of seed viability. It is also possible that some of the cultivars that exhibited this trait during the 2005 growing season suffered fruit bud freezing damage that didn’t kill the bud but did damage the ovary of the unborn seed. This fruit bud damage could have happened long before the bud ever came into bloom i.e. winter of 2004/2005 or it simply could have happened during bloom with freezing temperatures/and or poor pollen transfer doing the damage.