Up until this week, we had been receiving a lot of calls and e mails with concerns about turfgrass ant activity. The warm(er) weather in central PA and throughout the region over the last two weeks seemed to explode ant activity. This is somewhat surprising as mounding (and ant activity) should be declining from that of the earlier part of the summer. Work conducted in the early 2000s by Reid Maier and Dan Potter at the University of Kentucky documented the seasonality of mounding caused by the turfgrass ant (Lasius neoniger) in that region. Their work on Kentucky golf courses showed that mounds increased steadily between March and May, only to decline sharply after July or August. So, the good news is: the mounding should not be increasing. However, most people have asked what they can apply at this time of the year. Even if you have had major ant issues, I suggest waiting until next year before tackling the problem, and start with your control measures as soon as you see activity build in spring. Applying insecticides at this time of the year might clean up some of the ants on the surface, but will do little to reduce the overall colony or issues for next year. 
Turfgrass ant colonies are composed of a single queen (who is only responsible for laying eggs) and her daughters or workers (who are responsible for pretty much everything else). The males in the colony are similar to male bees (drones). They pretty much sit around and do nothing but wait for the opportunity to fly out of the colony to mate with a future queen….and most likely die in the process. The daughters (workers) are the muscle of the colony. They are likely the ones you have observed in the last few weeks, scurrying about the surface, foraging for prey. Inside the colony, workers take eggs from the queen and see that they mature into legless grubs, then pupae, before becoming an adult ant. When you apply a surface insecticide, you are wiping out some of the foraging workers. When they do not return to the colony, the queen can respond by making more workers. Therefore, if you can control the queen, you will have better results. However, if you can eliminate many of the foragers in the beginning of the season when the colony is just taking off, the colony may struggle to find prey to support the new queen’s egg laying activity.
Even the pristine turf at the Valentine Turf Research Center is not immune! A visit to Valentine revealed the characteristic mounding activity of the turfgrass ant. Mounds at Valentine were scattered across a rectangular research plot. However, the majority of mounds are located near the edges of the close mown turf. This is also what can be observed on sand-based rootzones on a golf course tee or green. The colony is formed by a single queen. The main entrance to the colony (and presumably the queen) is located on the edges of the green/rough border and not actually on the green or tee. Usually, this is composed of native soils. The mounds that we have an issue with on greens tend to be satellite mounds that are connected to the main colony. The turfgrass ant will dig horizontal shafts into green and emerge on the surface. The short height of cut and the ease of digging through sand rather than native soils, may allow the ants to create more mounds and forage more effectively.
So what could be going on with the increase in mounding activity in the Fall in the Northeast and Mid-Atlantic? It is important to note that the turfgrass ant is the dominant ant in open fields and pastures, and other disturbed sites (e.g. plowed fields). The same study conducted by Maier and Potter revealed that turfgrass ants responded to sand filled holes by increasing mounds in these areas. Could it be that recent aerficiation events have led to an increased ability for ants to move into areas and create mounds? We will see. Next season, our lab will be ramping up investigations into how the turfgrass ant responds to the turfgrass environment in the northeast. We hope to have a better understanding of how our cultural practices affect their presence and mounding activity.