Managing nuisance ants on golf courses
Ants can be a real nuisance on golf courses when their nesting and mound-building occur in high profile areas. Ant mounds disrupt the smoothness and uniformity of putting surfaces, dull mower blades and can smother closely-mowed turf.
Golf superintendents often report problems eliminating these pests with conventional insecticides. Further, ant problems in turf seem to be increasing nationwide. One theory to explain this is that residues of chlordane and other highly persistent turf insecticides used in the past have finally declined. Another theory is that replacement of diazinon (which is highly active on ants) with more target-selective soil insecticides has allowed ants to gain a foothold on golf courses. Whatever the reason, many superintendents need effective ant controls to reduce mound building.
Lately, my research team has been testing new approaches to managing nuisance ants using delayed-action baits and new classes of insecticides. The results have been promising and some of these new products are already catching on with superintendents. We are also studying the beneficial aspects of turf-infesting ants, especially their importance as predators on eggs and larvae of other insect pests.
The primary nuisance ant pest of turf is Lasius neoniger, a species that is widespread in the United States. In many areas, Lasius seems to be responsible for most, if not virtually all, ant hills on putting greens. Problems arise when the worker ants excavate underground nest chambers, pushing up small mounds of soil. Lasius is also common in roughs, fairways, lawns and other sunny turf sites; although there, the mounds are less conspicuous than on greens and tees.
Habits of Lasius neoniger
To manage these pests, you need to understand their habits. Like all ants, Lasius neoniger is a social insect. It lives in colonies consisting of hundreds or thousands of sterile female workers, but only one reproductive queen. The nest consists of shallow, interconnected chambers, seldom more than 10 to 15 inches deep. Each passage to the surface is topped by a small mound. The number of mounds varies from just a few to 10 or more per nest, and generally increases from early spring to late summer as the colony grows. The queen ant, with her eggs and larvae, remains underground and is fed and looked after by the workers.
How do ant infestations get started on putting greens? As colonies build in late summer, new queens and males are produced. These winged reproductive ants swarm out of the nests for their nuptial flights in late summer or autumn (August to October). After mating, the young queens shed their wings, burrow down, and excavate a small cavity in the soil. They remain underground over the winter and normally don't start laying eggs until the following spring. Successive broods are then produced until at last the colony is large enough to produce its own winged reproductive forms. Individual queens and colonies may persist for several years.
Lasius workers forage on the surface for small insects, insect eggs and other protein-rich foods. They also tend subterranean root aphids — just as ants “farm” aphids on plants above ground — to obtain the aphids' sugary excrement, called honeydew. Lasius is beneficial in most turf settings because it is a voracious predator of eggs and small larvae of cutworms, sod webworms, grubs and other pests (see photo, bottom right).
Our research has shown how important this predation can be. For example, when 1,600 newly hatched cutworms were released, one by one, near Lasius nests on collars or putting greens; the ants attacked and killed 62 percent of the larvae before they could escape. In another test, turfgrass cores on which black cutworm moths had laid eggs were implanted into fairways or roughs of two golf courses, and the fate of the eggs was monitored. Lasius ants consumed as many as 85 percent of the eggs in untreated roughs in 24 hours. In treated fairways where ants were less abundant, many more cutworm eggs survived to hatch.
Regardless of their beneficial aspects, ants quickly become a nuisance when they nest on putting greens (see photos, top right). Controlling them is difficult because fast-acting insecticides usually kill only a portion of the workers foraging on the surface, but fail to eliminate the queen. Pyrethroids and organophosphates (see the “Insecticide Update” on page Golf 7 for a list of chemicals registered for turf use) often will suppress mound building for several weeks after treatment, but then the colony recovers and new mounds appear.
Pest control operators who deal with nuisance ants around homes have found that commercial ant baits are an effective remedy. These baits contain delayed-action insecticides formulated on granules with attractive food substances. The worker ants carry the bait to the nest, where it is fed to the queen and her brood. Once the queen is eliminated, the colony dies out and the mounds are not rebuilt. However, ant species differ in their feeding preferences, so the type of bait is critical. We tested a range of bait types against Lasius on golf courses. We started with choice tests to learn which baits are most readily taken by Lasius, and then evaluated spot-treatment of nests on putting greens and tees.
Our research showed that Maxforce Professional Insect Control Fine Granule Insect Bait (Clorox Co.) containing the active ingredient hydramethylnon, and Advance Granular Carpenter Ant Bait (Whitmire Micro-Gen) containing abamectin, are highly effective against Lasius neoniger. Note that a similarly named product, Advance Granular Ant Bait, was not as effective in our tests.
Both baits worked equally well, but Maxforce is better suited for use on putting greens because of its smaller granule size and dark brown color (the Advance bait is yellow and more conspicuous). Sprinkled around the mounds, a small amount of bait will eliminate a nest in about 2 days. Then, once the mounds are raked or knocked down by mower blades, they will not be rebuilt. We're still testing minimum effective rates, but about ⅛ teaspoon of bait per mound worked well in our trials. Lasius workers forage during both day and night, so bait can be applied whenever it is convenient. However, baits that become wet lose their attractiveness, so withhold irrigation for at least 8 hours after treatment.
These baits are too expensive for broadcasting on fairways, but they are cost-effective for spot-treating putting greens. Superintendents who have tried them also report good results. Neither bait is specifically marketed to the golf industry, but their labeling does allow use on golf courses. They are available through distributors who carry products for the structural pest control industry. Maxforce is sold in a bulk container, as well as 10-ounce shaker cans that are convenient to use. The bulk container can be used to refill about 10 shaker cans. Never transfer baits or any pesticide to any unlabeled, or food, container. As with all pesticides, specific restrictions may apply in some states, particularly California. Spot-treating with bait allows selective control, while preserving beneficial ants in fairways and roughs.
Golf superintendents in the South now have another option for ant control. Recently, Chipco/Aventis announced registration of TopChoice, a granular insecticide for control of imported fire ants (Solenopsis spp.). It contains fipronil, the same active ingredient used in Chipco Choice for mole crickets. Applied at just 1.8-pound active ingredient per acre (87 pounds of product per acre), a single broadcast application in fall to early spring (November to March) will control fire ants for up to a year. That same rate also provides season-long control of nuisance ants (e.g. Lasius neoniger) and mole crickets. Those pests are listed on the label as secondary targets.
Fipronil is relatively slow-acting, an advantage for ant control. Foraging workers that contact or feed on the material do not die right away. This allows them to return to the underground nest where body grooming and exchange of food among nest-mates transfers the insecticide throughout the colony, including the queen and her brood. So, in this case, slower is better. Granular fipronil often provides 95 percent control of existing ants within four to six weeks after application, with enough residual to eliminate developing queens and also new, winged queens that may enter the landscape.
Fipronil represents a new class of insecticides called phenyl pyrazoles. These compounds target the GABA receptors of insects, a unique mode of action. GABA acts to “switch off” nerve impulses-blocking this action disrupts the insect's nervous system. Fipronil binds about 100 times more tightly to insect receptors than to those of mammals, providing useful selective toxicity. In fact, fipronil is also the active ingredient in Frontline on-animal flea control products.
TopChoice is presently labeled for use only in the 13 states: Alabama, Arkansas, California, Florida, Georgia, Louisiana, Mississippi, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee and Texas, where imported fire ants occur. The label wording is vague with regard to nuisance ants. It states that “The primary purpose of this product is for fire ant control” but also lists nuisance ants as secondary targets. Thus, federal regulations allow its use for nuisance ants. State requirements may vary, however, so be sure to check any supplemental state labeling.
For now, controlling ants with fipronil is only an option for southern turf managers. The manufacturer is seeking to broaden the fipronil label, so that granular products for nuisance ant control on northern golf courses may be available soon.
Regardless of whether you use baits or conventional insecticides, ants usually are easiest to control in the spring, soon after the mounds appear. At that time, the colonies founded by new queens are still small, and nests persisting from the previous year are weakened from overwintering. By controlling nests early, you may be able to avoid the buildup of mounds on putting greens that often occurs in late spring and summer.
Dr. Daniel A. Potter is professor of turf and landscape entomology at the University of Kentucky (Lexington, Ky.). His book, “Destructive Turfgrass Insects: Biology, Diagnosis, and Control,” is available from the GCSAA and PLCAA bookstores, or by calling Ann Arbor Press (800-858-5299).
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