The Ohio State University

Home TurfNotes I'm getting reports over a fairly wide area of the cool-season turf zone here in the northeastern half of North America! Each inquiry has been pretty much the same report. "There are little dead spots on my green, that looks a lot like early dollar spot damage, but when I dig into the area I find a little wasp like critter! What IS this??" In every case where a picture of the offending critter has been included in the email, the insects are obviously new ant queens. In most of the cases, I also find out that a surface insecticide (like bifenthrin, Dursban, Provaunt, or similar product) was applied within the last 10 to 14 days.

Now is the time that several species of ants swarm. Termites swarm in the spring to release new queens and drones (reproductive females and males) while different ant species may swarm over the entire summer. The infamous turfgrass ant, Lasius, is sometimes called the Labor Day Ant because they swarm in the last week of August into the first week or two of September. Swarming most often occurs on a warm evening following a recent rain event. The new queens are very large compared to the workers, often being 20 to 40 times the body weight. The males are much smaller, often only being twice the size of workers. Mating takes place while flying and once completed, the male drops off to die. (Termite males follow females to the new burrow where they stay together and continue to mate for life!) The mated ant queen drops to the ground and when she finds what appears to be a suitable place, she'll dig into the soil, often less than an inch below the surface. Most queens just hang out in these burrows until early next spring when she begins to produce eggs and the initial brood of workers. She feeds the worker larvae eggs that are produced entirely from her stored fat! By May into early June, the new workers begin to forage for food, and, if successful, can help build up a colony pretty rapidly. These ants usually don't produce new winged reproductives until the colonies are thriving and three to five years old.

I have often received reports of turfgrass ant queens throwing up small mounds of soil on greens and tees (usually noticeable in the morning after the swarming flight). I know of many superintendents who have panic at this sight and they quickly throw a surface insecticide down. Often they find the ants are not killed (it's still in the burrow) and I've not associated dead spots with this kind of treatment. So what gives? Many ant species, especially the Formica species or field ants, are known to produce formic acid as a kind of defensive repellent and herbicide! The Allegheny mound ant regularly clears grasses and plants from around its mound by using their mandibles to gnat into the plant stem, then tuck their abdomen under to squirt in the formic acid. A single treatment has little effect, but several dozen ants, working together can eventually kill offending plants.

I suspect that what is happening is that a new queen ant is landing onto treated greens and/or tees and as they attempt to dig into the soil, they encounter the insecticide. This causes them to react by squirting the formic acid which will cause the little dead spots. I can't find in my literature whether Lasius neoniger (the turfgrass ant) queens are capable of this, and I have only see pictures of the ants causing the problems which don't allow me to make species determinations. In any case, the dying queens are releasing small droplets of formic acid which are apparently killing little patches of the turf!

There's probably not much that can be done to stop this, especially if you have applied a surface insecticide before the ants swarm. Fortunately, the spots are small and the surrounding turf should cover up the damage pretty quickly. Most ants swarm for a week or two and then close up shop for the season. Just don't panic!

Photographs are courtesy of John Slade, superintendent at Laurel Creek Country Club, Moorestown, NJ.

Posted by David Shetlar