I live in Houston, TX, USA and fire ants are a nearly year long concern. I have had success treating mounds with Orthene as they appear.

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However, I had a Siberian Elm in my backyard that was infested with fire ants and I never managed to kill the colony. I could suppress it for a bit, but I would see a new mound within days. Not long after I started treating the tree and mulch around it regularly, it died (I've removed it since). It was near the end of it's lifespan (likely 30 years old).

Now I have a colony just starting up on a tree in my front yard (likely an elm as well, though it's much bigger than the other). In addition, my two year old loves this tree and plays around it constantly.

Here are my questions:

  1. Can Orthene harm my tree? Even over repeated dosages (a few tablespoons a month)?

  2. Is there a better pesticide that is less likely to harm the tree and my child? The Orthene is effective, but it is quite nasty.

2 Answers 2


I'd never use Orthene (or any organophosphate insecticide) where children play. But I've never had to deal with anything as nasty as fire ants, either.

Here are some thoughts, based on reading. See especially the links at the bottom of the page.

It sounds like you didn't get down to the queen with orthene, which suggests that a different treatment mode might be in order - either bait or a drench. Because you're working around tree roots, I suspect it may be difficult to get thorough coverage of the base of the mound with a drench.

Consider using a spinosad-based bait. It can be used as a mound treatment and/or as a wide-area broadcast bait. If I understand your situation, use it as a mound treatment - broadcasting will kill off other insects, especially other ants that compete with fire ants. (If you've got fire ants all over, then broadcasting is the way to go, with heavy dosing on the mounds as well.) It has to be used when the weather is dry - otherwise, it turns rancid.

Here's the advice from your county extension service. You may want to contact them. They'll have had infinitely more experience than me.

  • Thanks for this! The county link led me to a great site for my area: fireant.tamu.edu. Comprehensive rundown of available treatment methods and their efficacy. Feb 8, 2012 at 21:20

Ortho Fire Ant killer is the poison orthene, which is widely used on crops. So it shouldn't harm a tree. I have had great success controlling fire ants by spreading bait like Amdro over a wide area, including my neighbor's yards. It isn't fast, though. The Ortho is an immediate killer at a particular mound. Use Ortho on mounds that you can see and Amdro spread widely for all the mounds you can't see.

  • I used Ortho with good results. I've never used Amdro. I'll have to check it out.
    – J. Musser
    Jun 18, 2014 at 0:24

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