Q: We have a young oak tree that has developed cracks in its main trunk. What do you think is causing that? --M.B., Arcadia
A: The bark is probably splitting as result of the death of some of the tree's main roots. They may be dying after having suffered a mechanical injury, or gopher girdling, or an oak-root fungus infection. To check for oak-root fungus, dig at the base of the tree trunk and look for white fungus growth just under the bark. If you find such growth, but if the fungus has not progressed around the trunk, leave the crown area exposed, and refrain from watering around the trunk for a period. The only way to slow oak-root-fungus growth is to dry out the infected area.