How Apple Fruit Size Is Determined and Affected

An apple’s size is determined by the cells that make up the apple. The number of cells, size of each cell, and air space between cells all can play roles in fruit size. An average-sized apple has about 50 million cells. Some apples achieve their larger size by having a larger number of cells, and some achieve their larger size by having larger-sized cells.

Most apple growers strive to produce larger-sized fruit. To achieve this goal, growers should consider the …

Pollinating Apples

Figure 1. Bumblebee on apple blossom (Alan R. Biggs, West Virginia University)

Apples require cross-pollination for optimal fruit set and size.  Cross-pollination involves the transfer of pollen from one apple cultivar to another by pollinating insects, such as bees which are referred to as pollinators.  The cultivar supplying the pollen is called the pollinizer.  For successful pollination to occur, bloom periods must overlap.  Triploids apple cultivars, such as ‘Mutsu’, ‘Jonagold’, and ‘Shizuka’, cannot supply viable pollen and are unsuitable as …

Cedar-Apple Rust

Figure 1. Cedar-apple rust gall on eastern red cedar showing thoroughly wetted, gelatinous spore-bearing structures. (Alan R. Biggs, West Virginia University)

Cedar-apple rust is a fungus disease of apple and cedar and spends parts of its life cycle on each host. It is caused by Gymnosporangium juniperi-virginianae. The fungus can infect leaves and fruit of most cultivars in the eastern region. A notable exception is ‘Delicious’, which is nearly immune.

The most conspicuous symptoms on apple are bright orange, glistening …

Fire Blight of Apple

Fire blight

Figure 1. Blossom cluster and adjacent shoot with fire blight. (Alan R. Biggs, West Virginia University)

Fire blight is a destructive bacterial disease of apples and pears that kills blossoms, shoots, limbs, and, sometimes, entire trees (Figs. 1, 2). The disease is generally common throughout the United States wherever apples are grown. Outbreaks are typically very erratic, causing severe losses in some orchards in some years and little or no significant damage in others.

Fire blight

Figure 2. Apple shoot with fire …