By Greg Rubin, CNPS-San Diego Garden Native Committee member
Many people have been experiencing problems with many native species, such as Ceanothus, manzanita, mallow-like plants, and mounding perennials. One of the primary causes, surprisingly, appears to be invasion by Argentine ants! The increasingly hot, monsoonal weather of recent years greatly promotes them. What these ants are doing is placing insects like scale and aphids all over the ROOTS, which literally suck the life out of the plant from below, often undetected to those without the experience to pick up on the subtle clues...
Argentine ants appear to be responsible for other horticultural threats. They plant innumerable types of weeds, including Veldt grass, spotted spurge, petty spurge, purslane, scarlet pimpernel, chickweed, brass buttons, and dandelion, as well as natives like Miner’s lettuce and Purple three awn grass (they’re not very picky). Often massive infestations of weeds can be associated with ant activity; they give themselves away by the weeds they plant.
An additional concern, of grave consequence, is that these same ants may be spreading pathogens like Phytophthora. This is especially significant as there are virtually no treatments available for these water molds (Sudden Oak Death is just one example of this devastating group of pathogens).