When the temperature starts dropping it’s time to go on the offensive against ants. Ants are one of the biggest overlooked factors that lead to biological control failures. Many common species “farm” honeydew producing pests, including aphids and mealybugs. They eat and fight off predators, transport pests to new areas, and will even shelter aphids and mealybugs inside their ant mound. Cooler temperatures slow ants down, making them more vulnerable to attack by the vigilant farmer.One of the most effective control measures is baiting ants with low toxicity ant baits. We recommend using bait dispensers filled with liquid boric acid baits for sugar feeding ants. Dry granular borate ant baits can also be used. Boric acid won’t kill the foraging ants immediately, letting them bring the poison back to the mound where it can kill the queen. Don’t be alarmed if you don’t see results right away. Because of boric acid’s low toxicity, the same reason it is effective at killing whole mounds, it may take up to a month to see a reduction in ant numbers. Boric acid bait stations can also be used to prevent ant infestations. There are various strategies for bait station placement depending on the kind of ants and the amount and type of area needing protection. If the ants don’t accept the bait, try diluting it or adding more flavor. For example, ants in strawberry crops are more attracted to bait when strawberry juice is mixed in.
Physical disruption of ant nests provides more immediate results. Using a shovel or piece of rebar to break up the ground around the entrance to the colony forces ants that would be foraging to rebuild. If food supplies are low, the ants inside may eat their young. This allows beneficial insects to get to work without interference. Unfortunately, this is only a temporary solution and mounds will need to be repeatedly disturbed to distract the ants from tending to their honeydew source.
Other control measures you can use are nematodes, orange oil drenches, and sticky barriers. Read our Ant Bulletin and our founder Everett J. Dietrick’s paper Argentine Ants Must Be Suppressed for more information on ant control. This fall we’re also offering discounts on ant control supplies.
On an ant control side note, in a field study where they used only sticky barriers for ant control in an organic citrus grove, researchers found more aphids in the trees without ants! Their conclusion was that, as a side effect of excluding ants, they were also protecting the aphids from earwigs. After analyzing the populations of other aphid predators in their grove, they determined that earwigs are one of the main natural controls of aphids in the springtime. Populations of some of the other predators grew in response to growing aphid populations, but not fast enough to control them without the help from the earwigs.
Discussing the study at Rincon-Vitova, we thought of other predators we see a lot in orchards and gardens that would be blocked by sticky barriers – wolf spiders and ground beetles. Releasing aphid predators to back up the naturally occurring ones might have helped the aphid problem in the study grove. Or maybe another method of reducing ant interference without stopping crawling predators from finding the aphids, such as baiting, would have worked better in their case. Aphids can also be blasted off plants with a strong jet of water, which might be a good strategy if you are using sticky barriers. This study is a reminder of how complex these ecological systems are, and that we have to be alert to the unexpected effects our pest control efforts.
(The study mentioned, “Effects of the concurrent exclusion of ants and earwigs on aphid abundance in an organic citrus grove,” was written by Josep Piñol, Xavier Espadaler, Núria Cañellas and Nicolás Pérez and published in the August 2009 issue of BioControl (vol. 54, no. 4, pp. 515-527).)
-Alia Tsang, Bug Farm intern