What is the dividing line for US areas that have iris borers and those that do not? I have heard east and west of (what?) It might be possible to do a survey of who has / doesn't have borers and where they live?

Maryland - they are terrible here.

And we've heard from Ohio and Iowa that they have them.

DaisyDo said: Maryland - they are terrible here.

And we've heard from Ohio and Iowa that they have them.

Somebody on the forum from NY (Syracuse?) has said they had them.

And I thought I heard that Presby Gardens gets them in NJ.

Iowa has them for sure also Michigan.

Mn has them

Laurie, I think is her name, is in Nebraska. That's a smidgen east of the Rockies. Maybe we can hear from her.

This far this is the borer map. Anecdotally:

That was me - a horrible in infestation 2 years ago. I'm now applying special nematodes. But I'm wondering if there isn't also a moth trap to get them before they lay eggs. I had to dig up every iris plant, over 150 plants.

MamaFan said: Somebody on the forum from NY (Syracuse?) has said they had them.

And I thought I heard that Presby Gardens gets them in NJ.

None here in California.

The south has just more recently been getting them. You will find them in Virginia, North Carolina, Arkansas, possibly South Carolina. Not sure about the deep south.

Iris borer occurs within the native ranges of Iris versicolor and Iris virginica, which are its natural host plants. Basically, almost anywhere in the U.S. or southern Canada east of the High Plains.

They candefinitely be found in Pennsylvania.

Wheezy you can probably edit your map to add the additional borer states.

People in Montana, Idaho, Wyomng, Colorado, Utah, Arizona, and New Mexico especially need to weigh in on this. Just say no, if you don't have them.

DaisyDo said: Wheezy you can probably edit your map to add the additional borer states.

People in Montana, Idaho, Wyomng, Colorado, Utah, Arizona, and New Mexico especially need to weigh in on this. Just say no, if you don't have them.

Well Colorado has 2 climates, east and west of the rockies. It would be interesting to hear from them.

KentPfeiffer said: Iris borer occurs within the native ranges of Iris versicolor and Iris virginica, which are its natural host plants. Basically, almost anywhere in the U.S. or southern Canada east of the High Plains.

That's very interesting about iris versicolor and iris virginica. I will have to research that more. Where did you find this info, Kent?
I googled and found nothing. I have both of these plants by the way but my yard had borers before I got these 2 plants.

"east of the high plains" would suggest that the continental divide is not the actual boundary for borers.

caitlinsgarden said: That's very interesting about iris versicolor and iris virginica. I will have to research that more. Where did you find this info, Kent?
I googled and found nothing. I have both of these plants by the way but my yard had borers before I got these 2 plants.

I suspect that information will be hard to find with a google search because all of the results are geared towards control of borers in garden irises. It is, however, common knowledge among the butterfly/moth researchers I interact with on a regular basis.

If you think about it, though, it's not really a controversial statement.

1. Iris borers are native to North America.
2. The larvae are only know to feed on plants in the family Iridaceae.
3. Prior to European colonization, there weren't many options other than Iris versicolor, Iris virginica, and possibly the cristata-type irises for the borer larvae to feed on. There just aren't that many species of Irids that are native to North America. The rhizomes of Sisyrinchiums are far too small to accommodate an iris borer, Nemastylis grows from small bulbs that also wouldn't suit an iris borer, etc. The only real mysteries are that the borers don't seem to bother the Iris species that were native to the Gulf Coast (the "Louisiana Irises") and I don't think they have been found in Iris missouriensis (which is widespread in the western third of the US).

You might say that gardeners, by planting various types of irids from other parts of the world, have been a real boon for iris borers. We have greatly diversified their options for larval host plants. Even today, though, if you overlay the range map of iris borers on the combined range maps of Iris versicolor and Iris virginica, they still correlate quite nicely.

"The only real mysteries are that the borers don't seem to bother the Iris species that were native to the Gulf Coast (the "Louisiana Irises"

Actually, yes they do, at least here where they are transplanted into Maryland! In about 2021 I didn't think I needed to clear away old leaves from my patch of Louisianas, and that fall I discovered that most of those very narrow rhizomes were all hollowed out by borers. I nearly lost Red Velvet Elvis entirely. Since I started meticulously bagging every scrap of dead leaf by early spring, they are recovering.

I wonder if it is just a question of time before borers get to the western states. I was trying to think of an explanation for why the moths are limited to east of the Rockies. It isn't because of temperature. Is it that they just can't fly high enough (sounds silly) and whatever borers get transported interstate in rhizomes aren't enough to sustain a viable population?

When you think about it, there are bird species also that are limited in range. For example, no cardinals here in the West, although they are endemic in KS and IL and other Midwestern states. So I think there is something to it that the Rockies form a natural barrier, for whatever reason.