If the branch originates above the graft union, then keep the trees. That will be quicker and cheaper than replanting. You can make a new tree out of just one shoot. With an established root system the tree will grow rapidly.

Thank you everyone for your advice and suggestions. Please keep them coming. Yes, I am deeply mourning the loss of the tree. I fought to save it and lost! The facts were that the oak made my neighbor and her little daughter sick with allergies and that their current house remodel included destroying half its roots and removal of half the tree which would have rendered it unsafe and caused its slow, or not so slow, death! For these reasons, as much as I love oaks, I can't plant another one. My neighbors love palms which is why the Foxtail with its instant height and canopy was my first thought. The lowest temperature on record for our city is 19 degrees in 1981. However I have no idea how low the temperature in our microclimate has fallen. I have read conflicting freeze temperatures for the Foxtail. Can anyone clarify? Also if it is fairly mature, say 18 feet or so, what is its likely life expectancy? I am now investigating some of the other species kindly suggested by you fellow Florida gardeners. Can anyone suggest where I might purchase a Tipuana Tipu? Further ideas and suggestions would be very gratefully received.

Ideal planting time is spring when temperatures have warmed up a bit. That gives the palms a long period of warmth for roots to grow. This is true for all tropicals/subtropicals. 8 feet sounds like plenty of room, just don't buy giant-size palms to begin with. The bigger they are, the touchier they are. 15-gal. would be a good size. If you are planting more than one, be sure to leave room for mature size, which will be substantial. The book "Palms for Southern California" lists mature height at 30 ft. and spread at 14-16 ft., I'm guessing slightly smaller at your latitude. Some of the bismarckias are more blue, some more green. The silvery blue seems to be the coveted color, and the blue can tolerate colder temperatures than the green (21 vs. 28). Some will look reddish if grown in full sun when young. Here is a link that might be useful: More info.

What kind of black ants? Big black ants like carpenter ants or little black ants like fire ants? If they're carpenter ants, spray won't touch them, and they'll hollow out your tree until it dies. You have to get to the next to kill carpenter ants, which is very deep underground, and may not even be close to the tree. Use Amdro and see if that gets them. Carpenter ants are nearly impossible to get rid of without professional help.