We have two (one male, one female) Heartnut trees that are around 15 years old, twenty feet or so tall and have been very healthy up until this spring. They were starting to leaf out in April and then were hit by a killing freeze of 16 degrees. All of the new growth died back and we've noticed both trees "bleeding" sap at various points along the branches. Is this their demise?? We would hate to loose these wonderful trees. Help!!