I know I’m a bit late to your question. I’ve have been experimenting with controlling leaf cutter colonies in Bolivia for a while now. I would be interested in hearing about things you have tried. What has worked for you and what has not.
I hope to write a more extensive piece on leaf cutters soon. They are an extremely challenging and complex problem to control. They learn very quickly and so it usually takes a lot of different approaches to control them. I’ll quick highlight some of the things I’ve found.
Cotton: For protecting specific plants, a ring of cotton or similar substance (fluff from Silk Floss Trees, Ceiba species) gets caught in their feet so they hate crossing it. If you can tie it to the trunk of a tree it works best and down in the soil it gets matted down quickly.
Clutter their highway: You may have noticed they like neat, clean highways to their collections sites. Make your plants as hard to get too as possible: messy thick fibrous mulch, perennial peanut, water/oil barriers, etc.
Diverse/balanced ecosystem. They love a high diversity and density of plants to choose from. If you have a large wild space for them to choose from, it helps keep them away from your garden. Also having a high density and diversity in your garden spaces will help ensure that you don’t loose everything.
Distractions: You can specifically plant plants they really like to help distract them from your other plants. In my area they love Moringa, especially Moringa stenopetala. If you can protect the trees until they are fairly mature, they seem to be able to take a lot of damage from leaf cutters and then the ants leave many of your other plants alone. Putting a compost pile nearby also works. They love to walk off with your plant scraps.
-Poison: Poison doesn’t often work well because their colonies are huge and they don’t eat the poison like most ants. They eat the fungus they grow in their gardens underground. So killing the fungus is the goal but very difficult. Plants like Jack Bean and Sesame will kill their fungus however as soon as the ants catch on, they will never touch those plants again. Similarly with man-made poisons, they learn fast and will never touch it again.
-War/Peace: So I tend to make peace with them during wet season. They have lots of food to pick from and intentionally feeding them their favorites during this time keeps them away from my garden. During dry season however, food for their fungus becomes more scarce and they start taking everything in site. They are also most vulnerable during this time. This is when I launch all out war on them to try and knock the colony back. Boiling water down their nests, dropping toxic plants around their nest, encouraging nearby colonies to fight with each other, releasing natural predators or parasitic fungal spores, etc.
That is a quick overview of what I’ve found. I hope to write up more info on this topic soon as it has been one of my biggest problems working in South America. I’d love to hear more about what you have tried!