Ask the Garden Sage

Ask the Garden Sage: Plant-stripping ants

2014-08-10T00:00:00Z Ask the Garden Sage: Plant-stripping antsBy Peter Warren Special to the Arizona Daily Star Arizona Daily Star

My question involves plant-stripping ants that remove the leaves from bushes and cacti, killing some on our property. They have ant beds and are active early in the day. We used a pesticide on some last year, with some success. Do they become immune to the spray? Can we use it extensively on two-acre lots? Is there some other available pesticide that will eradicate the ants?

A: Leaf-cutter ants (Acromyrmex and Atta species) can be difficult to manage. Their nests are underground and it’s not easy to locate all of them. You can’t eradicate them; you can only hope to contain them. There are two methods you might try to make plants less hospitable. First, you can spread some diatomaceous earth around the base of the plants you are trying to protect. Crawling on this stuff is abrasive to ants; it damages their exoskeletons and causes them to dehydrate.

The second thing is a sticky barrier, such as tanglefoot, applied to the base of the plant that will prevent ants from climbing up the plants. Insecticides can be effective but many of them are contact poisons and need to be applied when the ants are there. There are some insecticides that can be applied to the nest if you can find it. Since these ants are after the leaves, insecticides formulated as baits are not usually effective. There is one sold under the trade name Amdro Ant Block that is labeled for the control of leaf-cutter ants in landscapes. However, it is not a permanent solution and should not be used near food crops such as vegetable gardens. Much of the damage is done at night on days when it is hot out so be prepared to wait until dark if you want to see them in action. Insecticide resistance does occur with chemicals we use frequently so it is always good to rotate types of chemicals if you go that route. As with all pesticides, please read the label and follow the instructions to assure safety to you and nontarget organisms like pets, bees, and birds, and to abide by the law.

Yesterday evening we noticed a large number of giant mesquite beetles in a couple of branches on the seedpods obviously mating. 1. Will the females disperse to lay their eggs on other food sources? 2. Will my tree lizards eat most of the young? 3. Why the large number in one place? I consider myself quite observant and have not seen these before.

A: These insects are actually called giant mesquite bugs (Thasus neocalifornicus) and differ from beetles in that they have piercing-sucking mouthparts and front wings that overlap, among other characteristics. They are fairly common in the foothills of Tucson but not always in the same places. They are not numerous every year it seems but someone always sees them and asks about them. They are only found on mesquite trees so your other plants are safe. Since they are sap feeders and not usually found in large numbers, even the mesquite trees are safe. The young are in danger from predators but because of their warning colors (red and yellow) they have some protection. Some of them will always survive.

Can you identify this flower? It looked like a brown stick without leaves until it grew a green bulb at the top and then out came beautiful pale pink blossoms, one at a time. So far, there have been seven blossoms — several have died by now. This year it sprung from a pot — last year it came out of the gravel in the front yard. It’s about 2 feet high.

A: It looks like Amaryllis belladonna (aka “naked ladies” because of their pinkish flowers and lack of foliage at bloom time). They are striking to see without the foliage we expect to see on a lily; the foliage appears later. They are originally from South Africa and have naturalized in Mediterranean climates. They do well in places with warm dry summers and can last many years.

Peter Warren is the urban horticulture agent for the Pima County Cooperative Extension at the University of Arizona. He works with landscape professionals, urban farmers and homeowners to promote integrated pest management and best management practices for desert horticulture in southern Arizona. Questions can be sent to plwarren@cals.arizona.edu

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