We have found that corn grits work better than orange oil. Use the regular or quick grits, not the instant grits.
The latter have already been expanded. If in doubt, check the weight on the box and the quick grits will be at least twice as heavy for the same volume as the instant grits.
We find that the quick grits work much better than the orange oil which has the tendency to kill grass. The grits kill all of the ants within 1 to 2 days while the orange oil may not. For that matter, grits works just as fast as most pesticides. But, the ants may come back as they will continue to hatch. In that situation, just apply more grits.
As far as the dried molasses and beneficial nematodes, ours were doing fine until late August. Before then if a mound started, the ants would die out within 3 or 4 days. But, with the hot, dry weather I believe the we have lost some of our nematodes near the surface. Some mounds do die, but some get large and have required the grits.
My wife claims she like to listen to the ants going pop.
David Griffith, Plano
Here is my take on why grits or cornmeal can inhibit Fire Ants.
Fire Ants vary their diet seasonly. Typically they go after proteins more in the Summer(worms or dead bugs or meats or animal oils, etc.). In the Fall and Winter, they diet more on carbohydrates. This is when starches (grains) are more appealing to their diet.
Probably what makes the cornmeal (or the cornmeal nature of grits) more effective in inhibiting Fire Ants is that they feed this to substance to their larvae in order to break it down into a digestible food source for the adult Fire Ants. Their food source normally is based upon a type of fungal breakdown in concert with their young. This is inhibited by the cornmeal. The antifungal nature of the cornmeal/grits upsets this feeding cycle where the adults can not obtain their final food product (a fungus-based food secreted via the larvae). Essentially, the Fire Ants start to starve because their primary food source isn't happening -- it has been "infected" as a result of the antifungal activities of the grits or cornmeal.
Some of the details of this cycle might be rough around the edges on my rendition, but this is probably why people find success with grits this time of year. In the summer, grits will probably be less effective.
I am no Scientist, but I do a lot of research along with experimentation in the real world.