Ants! Ants! Ants!

My lawn (and garden in general) is home to the world's population of ants. They throw up little loose mounds of earth all over. One paddock was ruined over about 5 years by anthills which grew & grew until the only solution was to have it ploughed up and re-seeded.
It's almost impossible to sit on the lawn without having them encroach on rugs & food. Children in my family don't like picnicking on the lawn (a classic summer activity) because of this. The ants attack fruit trees, especially pears and plum, and cause the leaves to curl; they farm aphids on shrubs like Philadelphus with the same result and are in all the borders & beds. I have looked for an effective systemic wide-area liquid spray but with no success. What do commercial gardeners / farmers use? Surely there must be some large scale method of eradicating these pests? Any ideas welcomed.
Thanks. lindyco

 

Ants!