Fruit cracking is often a
physiological response to
environmental conditions, such as
irregular water supply. It’s common
in the second part of the growing
season that starts in July while the
fruit is still relatively small and can
go up to harvest.
Two other factors,
boron deficiency and apple scab
lesions, can lead to cracking as well.
But, by far, the response to irregular
water supply is the main reason
for this phenomenon.
In order to understand how
cracking happens, we have to
consider that there is a set number
of cells in an individual fruit. Those
cells expand to accommodate and
retain water absorbed through the
skin and by the root system.
With
sudden influxes of water and low
rates of evapotranspiration due to
high humidity and low wind, the
cell walls will rapidly expand and
stretch until they reach the breaking
point. That breaking point is not
the same for all apple cultivars.
Different cultivars have different
epidermal and sub-epidermal
thicknesses. Cultivars with thicker
layers are more resistant to
cracking.
There are several other contributing
factors to cracking:
- Poor tree vigor – stressed trees that are suffering from malnutrition will not produce abundant foliage and strong flower buds. The fruit set on stressed trees is low, coupled with excessive fruit drop. Those trees will have poor growth resulting in reduced canopy size or a smaller surface for evapotranspiration that leads to increased fruit cracking.
- Very late and hard pruning – can affect normal growth of foliage leading to overall reduction of surface area for evapotranspiration that results in fruit cracking.
- Poor fruit set and/or over-thinning – few fruits left to absorb all the sudden, excess water can result in fruit cracking.
-
Apple scab infected areas – are not
capable of cell division and
expansion that results in
cracked fruit.
Susceptible Cultivars
The most susceptible cultivars to
cracking are Stayman, York Imperial,
Wealthy, Fuji, Gala and Golden
Delicious, mainly late in the season.
For Stayman and Wealthy, the cracks are found on the green cheeks as irregular lines that could be barely visible or extend deep into the flesh and circle the entire fruit.
The York exhibits numerous horizontal cracks, mainly concentrated around the fruit’s equator nearing ¼ inch deep.
When fruit is close to maturity, Gala and Golden Delicious cultivars develop cracks around the stem in the stem cavity.
The shallow cracks often heal and the fruit develops scars that resemble cork and deform the fruit. Deep cracks, especially ones on fruit near maturity, are attractive to many insects and susceptible to secondary pathogens that can lead to decay.
Prevention
What could be done to prevent this? There is not much we can do about the weather, but cultivar choice and tree care is in our hands. Avoid the crack-prone cultivars mentioned above.
Tree maintenance, such as pruning, fertilization, fruit thinning, and insect and disease protection, should be provided on a regular, timely basis in order to minimize fruit cracking.