Fighting Argentine Ants – killers of California natives and the scourge of the kitchen

If you live anywhere in a suburban area, you have encountered the plague of Argentine ants (Linepithema humile), those little brown irritants that crawl up your leg while reading a book outside, cover your kitchen counters with massive troop movements, wipe out native harvester ant colonies (which are the primary food of our native horned lizards), and have now been revealed as possibly one of the key predators of California native plants.

These little buggers appear do their dirty work by forming colonies near or around the base of their victim, collecting sucking insects like scales from the surface and placing them on the roots (they use these plant sucking creatures for the sweet “honeydew” fluids they excrete), and possibly spreading pathogens to the plant. How do you know if your native plant has been attacked? The lead symptom it typically death. Suddenly, the leaves start to look sick and limp. By the end of the week the leaves are drying out and beginning their journey to various shades of morbid brown.

Here at the Chaparral Institute garden we have lost a number of plants suddenly – a huge flannel bush (Fremontodendron californicum),  a gorgeous white bark ceanothus (Ceanothus leucodermis), and three beautiful Catalina ironwood trees (Lyonothamnus floribundus). Fortunately, we still have one ironwood left. But around the end of August it was looking sick. By early September the leaves were brown.

Not knowing the cause, we initially chalked it up to possibly over-watering (we didn’t) or some kind of soil-borne disease (not sure what). That was until we had the fortune to remember a chat we had with one of southern California’s premier native plant landscapers, Greg Rubin. Greg was the first to discover the possible impact of Argentine ants on native plants and had devised a technique to fight back

We pulled back the back of the ironwood at the tree’s base, and yup, out spilled an army of Argentine ants. They all came out from directly under the portion of the branched trunk that was dying.

We called Greg and he provided us with a detailed recipe of nutrients, insecticide and a dash of an organic compound that is known for killing pathogens. We poured the solution into a basin around the tree as per instructions.

It has been about a week since we applied Greg’s recommended treatment. So far, so good. The ants are gone and the left branched trunk seems to be maintaining itself.

Here’s the information on the information you need on how to control Argentine ants.

If you want to contact Greg for advice on any suddenly ill native plants in your garden, please visit his website.

Oh, here is the flannel bush we lost several years ago, before it dropped suddenly.