There are a few things that can cause bark splitting or cracking. Extreme heat or fluctuating temperatures followed by a frost event can cause sunburn and sunscald. Mechanical injury (e.g. the trunk was hit with a string trimmer) can cause cracks in the bark. Cankers caused by plant pathogens can sometimes resemble splitting or cracking in their early stages. Sunburn or sunscald is the most common cause of bark splitting in young trees. With sunscald and sunburn, the damage will usually appear on the south or southwest side of the tree. Apple trees, and fruit trees in general, are susceptible to frost cracking and sunburn. For more information on sunscald and sunburn, refer to https://pubs.extension.wsu.edu/environmental-injury-sunscald-and-sunburn-on-trees-home-garden-series.

The main risk is that a wood boring insect or pathogen may enter where the tree has split opened. In this case, it looks like it has some white wood decaying fungus growing on the trunk. Wood decay is usually a disease of older trees, but it can affect young trees that have been wounded (ex. split bark) or weakened, allowing an entry point for the fungi. The main concern is that wood decay can weaken a tree, which may lead to limb breakage and/or uprooted trees during wind or ice storms. It can also decrease the vigor of the tree and cause dieback. At this point, all you can do is try to keep the tree healthy by fertilizing it in the spring and early summer, and irrigating the tree during the hot dry summer months. When irrigating, try not to wet the trunk of the tree with sprinkler irrigation, instead use drip, soaker hoses, low trajectory sprinklers, or manually water at the base of the tree. For more information on wood decay, including management practices, refer to the following: https://ipm.ucanr.edu/PMG/PESTNOTES/pn74109.html.

In the future, if you plant a new tree, you can prevent sunburn or sunscald by painting the trunk with a 50:50 mixture of white latex paint and water, or place a white trunk guard around the trunk. However, now that the damage has occurred, it is best not to paint or cover it, since the paint or trunk guards can trap moisture causing further decay. You can use a knife to try to trim away excess bark. This Cornell University factsheet provides a few tips on how to manage bark splitting: http://plantclinic.cornell.edu/factsheets/barksplitting.pdf

Hi, 

Thank you so much for the information.  One more question - what would be the best fertilizer to use?