92aea58e____Friends_of_the_Urban_Forest__Possible_Causes
[Symptom] In rare cases of frost, some plants will partially or fully die back. [Solution] Don’t prune off the frost-burned branches until you are sure no further frosts are expected. The outer foliage is keeping the inner foliage warm. To prevent frost burn, keep plants well watered. Cover with an old sheet or towel at night if frost is expected, trying to leave an air gap between the sheet and foliage. Uncover during the day. Outdoor rated string lights ("Christmas lights") in the tree at night can also help, especially if it is covered. Jacaranda (Jacaranda mimosifolia) and New Zealand Christmas trees (Metrosiderus excelsus) are some of the more common San Francisco street trees subject to frost damage. [Possible Causes] 
Frost Dieback
Common Problems & Disorders | Friends of the Urban Forest
Possible Causes