33 yr. old oak tree in northern california. 3 trunks coming up from base, 2 of which have leaves not growing at the top for 4 years. on treatment with a systemic pesticide. Might we save the one limb which still grows leaves and cut off at the base the 2 limbs which seem to be dying?
Santa Clara County California trees and shrubs
As long as you follow general good 'tree pruning tips' (google this phrase for a wide variety of publications and Youtube video clips), there is no problem in cutting off the dead trunks. It is best if you do not cut into the healthy wood. Since you are in the infestation zone, your tree may have the 'sudden oak death' fungus. See http://www.suddenoakdeath.org/ for more details. The best practice would be to NOT sell any firewood out of the county. If one trunk is still doing fine, you probably do not need to try systemic pesticides as there could be many different pests and choosing the best treatment will require hiring a professional arborist.