I have been fighting those little "buggers" ever since I bought this house in 2001 when my wife and I retired. I have a pretty large yard (1+ acres) and have some open land around me. The ants always seem to come from somewhere else and they seem to like everything in my yard including a 50 foot Chinese Tallow, a fence line of oleanders, a pear tree and the ash trees.
I went down to Valley Garden Center and was told to buy some foul smelling white powder called "Acephate". It kills the ants real good but is short term and you need to put out a lot to really get at them. (I have and still use this stuff.)
I called the Ags down in Weslaco and talked to their head entomologist (sp?) named Stormy Sparks. I said that at the time he had no good solutions but would like to drive up and try out several baits in my yard. He did but had real mixed results. After a couple of years I called back and talked to another fellow down there and he suggested that I use some stuff available at WalMart called "Over and Out". I just happened to be having a problem with the ants in my pear tree and I used this stuff. The ants disappeared and never came back. (Coincidence?)
The guy that does my spraying around and in my house told me that he had the commercial version of the "Over and Out" and he would try it out for me and sprayed around my tallow tree. They left there and have come back after a year from another direction.
My neighbors and I irrigate at the same time and one of the nests was in his yard. The last time we irrigated, the nest in his yard caved in and made a mess. I really hate those ants!
If I were you I would get some of the Acetate and keep it around and try the "Over and Out" later. Good luck!
If you hear of a good solution be sure and post it here so I can try it.
http://fireant.tamu.edu/broadcastbait/products/overnout.cfm[This message has been edited by oldvalleyrat (edited 7/5/2011 3:39p).]