Combating Garden Ants
Gardeners’ Corner | Questions and Answers with Local Experts
By Dan Songster, 2016 November
This column is a regular newsletter feature offering chapter members and local experts a chance to briefly share information on many things related to gardening with natives. The question for this newsletter is: “Many of us had a terrible time with non-native ants this past summer and fall. What (if anything) did you do to combat them successfully in your garden?” 
NOTE: Recently Greg Rubin, a San Diego based landscape designer and installation expert spoke to our chapter. With his broad experience with natives and successful landscape designs, he has dealt with all manner of problems. In his talk he emphasized the critical role that non-native Argentine ants play in the importation and support of various sucking insects like aphids and scale to the detriment of our native plants, especially in garden situations. The following is Greg’s “brief” response to the question about ant problems in the native garden.
Greg Rubin
“As you probably already know if you attended our recent presentation with the Orange County Chapter of CNPS, Argentine ants may be one of the single greatest causes of mortality in native landscapes. Although there are certainly lots of other reasons plants can die (overwatering, underwatering, fertilizer, root pathogens), I usually start by looking for ants. If they are present, especially in the rootball, then I treat the infestation first, and that often resolves the issue. I’ve even been able to save dying Ceanothus!
Without getting into too many details, if the plant is in imminent danger of collapse, I first pull the mulch back from the base and wait a little bit to see if the ants start to swarm. Other indications would include weeds (like Veldt grass or spurge) growing right around the base of the plant, and general instability (looseness) of the root crown. When ants nest they remove soil from the roots so they can attach sucking insects like scale and aphids, which begin to weaken and eventually kill the plant below ground. You may also see direct evidence of scale on the lower trunk or even up in the branches.
A plant that has begun defoliating may need immediate attention in order to save it. This usually involves using some form of insecticide that has both systemic and contact effects. I only spray the plant itself and about 1.5X the shrub diameter on the ground. Because this can be harmful to pollinators, including bees, it is essential that this only be applied when the plants ARE NOT BLOOMING! Since there is a 1-3 month residual, you don’t want to spray after about the end of October for spring bloomers. Fortunately, ants are usually dormant during the cooler winter/spring months.
I have found that the most effective long-term approach with the least potential for harm is to use baits.
Advion arena bait stations can be placed along the trails, up to 3-4 per area for heavy infestations. Gourmet liquid ant bait is another product that is dispensed in KM Antpro stations (or similar) and is approached differently. Stations are usually set up in a grid about 50-75 feet apart and must be shaded. You can use a slightly tilted bucket if there is no natural shade in the particular spot. I like to use both methods together as ant appetites seem to switch between protein and sugar (Advion is peanut butter based and GLB is more sugar based). The good thing about baits is that they are dispensed in a way that targets Argentine ants and not native ants. There are other very promising approaches on the horizon but they still need to be tested and vetted for effectiveness and safety. Best of luck in the ant wars!”
Laura Camp–‐“Combat Max Ant–‐killing gel, active ingredient Fipronil, is working well for me, indoors and out. Apply a small amount (out of direct sun) in the ants’ path every 5 feet each day until the trail disappears. Follow directions on the label!”
John Gossett–‐“I have not had an ant problem this year, perhaps I go drier than most? I have not watered the backyard this year except for some new plants a few times in the spring, and the front has only gotten three waterings this year.”
Leon Baginski–‐“Liquid ant bait that comes in a small self‐contained dispenser. Cut off one end and the ants just line up, drink the stuff, take it back to their queens and slowly you can watch the size of the ant trails decrease. Took several boxes of the stuff but it had an impact.”
Alan Lindsay–‐“Until I heard Greg Rubin’s talk my only concern about ants was keeping them out of the house—I have my own discovery and drenching method to help control those populations of ants. I have only used Advion once and it was inside the house on the kitchen counter. I put several beads of it on the splash board and it did exactly what Greg said it would. It attracted more ants and by morning they were gone and never came back. I plan to try this product outside now.”
Dan Songster–‐“Ants have been an ongoing problem, giving aphids, scale, mealybug, and other pests a helping hand by moving them around on some of my native plants. We also know they tend to fight off any good insects that want to eat those pests. Dry conditions in the last few years have helped slow this damaging process but they are still a problem. Bait stations used as directed seemed to slow them quite a bit.”