I live in an area where there are multiple varieties of ants in large quantities and they can be a huge problem in the garden, especially the leaf-cutter ants. Here some of the ants do not scurry across a table to pick of bits of food, they pull up a chair. Last year particularly i had leaf-cutter ants which are problematic. I have a few things to consider before choosing an ant remedy. My garden is organic, my garden is a host for many kinds of beneficial insects from butterflies and bees to lady beetles. So i can't even use some organic solutions like neem and spinosad, because they can't tell the difference between a "good" bug and a "bad" bug. Last year the garden was attacked by leaf-cutter ants for the first time in 8 years. The leaf-cutters are farmers that come in the night between 10pm-12pm and, if there are enough of them they can defoliate a good sized tree over night. I call them "farmers" because they return to their tunnels carrying small half round pieces of leaf on their heads (they look so cute) and use them to grow a type of fungi that feeds the colony. Over the years i have tried dozens of organic solutions. My garden is walled, in the Spanish style, with 3 walls plus the back of the house. Ants seem to follow pathways, so if i catch ants on the walls i spray them with a solution of water, dish soap, cinnamon oil drops and clove oil drops. If i don't have the spray bottle handy i squish them with my hands. Either way, i can kill a lot of ants. Ants are not stupid, they eventually will cease to come into the garden, or they will find another pathway. Both the spray and my hands are instantly deadly. In my garden i look for signs of ants making themselves at home, i.e. tunnel building mounds of earth, for example and destroy them before they can settle in the garden, generally using a shovel or spraying the solution (described above) into the hole. I don't want to stay up all night killing leaf-cutter ants. Now, the bees, butterflies, lady beetles are not active during the night. I don't have access to many products made in the US, but i do have access to food grade diatomaceous earth (DE), which is not "earth" at all but a powder, which will kill ants and slugs, etc, so it is insecticide when dry, a good fertilizer when wet, and people drink a solution of it for some health reasons (If it is food grade). Now some caterpillars destined to grow up to be butterflies are also active at night, but are on their host plants eating and not crawling around on the ground. So i can surround a plant at the base with DE where the earth is dry in the evening before dark. DE is not effective as an insecticide if it gets wet. I can put it on some leaves where they may be in contact with other plants or the wall making sure the ants can only access is the base of the plant.
It may take 3 nights or so of this treatment to alert the ants that this powder is going to kill them. Also, oddly enough, if they bring the powder back to the tunnels (either on themselves or on some leaves), the fungi alert the ants to not bring it back again. The ants are not killed by ingestion but by the diatom skeletons cutting into their bodies and legs. In this year i have already kept ants (not leaf-cutters) from planting aphids on some of the plants and i've eliminated the slugs. I am now ready to take on the leaf-cutters if they should return unless they return during the rainy season. I haven't yet figured that out. Many of the plants are too large to put burlap bags over them. Yes, i am still working on what to do during the rainy season.
www.dirtdoctor.com also has some remedies for fire ants using citrus oils.
