How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask tex-eng Your Own Question
tex-eng, Engineer
Category: General
Satisfied Customers: 705
Experience:  Engineer, very good math skills, problem solver and researcher
Type Your Question Here...
tex-eng is online now
A new question is answered every 9 seconds

How do I get rid of iris borers

This answer was rated:

I have an approximately 3 foot long row of irises (transplanted from New Mexico to my garden in Michigan). I noticed, long after the blooms disappeared that the greenery on one end of the row was lying flat and there was a strong smell of cat urine. When I started digging I found borers - white caterpillar. I dug out the section that appeared affected, but am worried about the remainder of the row. Can I dig up the rhizomes now and save them for transplanting later, or is it hopeless?
Hello Sara, hope you are doing well,

The articles that I found give a very detailed explanation about the iris borer problem and how to deal with it, here are two:
(find the title "Iris Borer of Past, Present and Future?" and especially the sub-title "Control")
(Find the question starting with "Q. My mother bought me some iris bulbs last summer." and read from there)

These two articles contain abundant information about the insect as well as to how to get rid of it and digging the plants.

Let me know if you will need further help.
Customer: replied 10 years ago.
Reply to tex-eng's Post: I have read articles like this already and am still unclear as to what I should do at this point. Do I dig up the rhizomes and clean them and replant in the fall or spring? Or do I let them sit in the garden and hope the borers haven't spread?
Hello again,

Ok, now since the adult borer is a moth and lays eggs on the leaves between August and September, if you dig the rhizomes and replant them in the spring you have the chance to get rid of most of them. However this may not be enough, I would also suggest that you use Bayer Advanced Lawn Season Long Grub Control Ready to Spread Granules, which contains Imidacloprid (Merit) which is a very effective chemical against iris borers. Read the directions before applying, it needs to be applied in the spring. If you can't find it in your area you can find it online, like this:

For other pesticides and more info about terminating the iris borers check this web page:

Hope these help better and let me know if you have further questions.
Customer: replied 10 years ago.
Again, I'd already discovered this much doing my own online searches. You've presented me with no new advice.
Hello again,

Here's the question part of your post:

I dug out the section that appeared affected, but am worried about the remainder of the row. Can I dig up the rhizomes now and save them for transplanting later, or is it hopeless?

These are the answers to your questions:

Q. "...but am worried about the remainder of the row."
A. You are right about worrying, this insect may destroy all of your plants.

Q. "Can I dig up the rhizomes now and save them for transplanting later, or is it hopeless?"
A. Yes, you can dig the rhizomes now and save the ones that haven't been damaged by the larva for the next spring.

If you have any other question(s), not possible to discover on the Internet, I will be more than glad to answer them.

Have a great day!
Customer: replied 10 years ago.
I guess the unspoken questions still remains - if I dig up the rhizomes, what do I do with them to assure they're ok? Soak in bleach solution? Just let them dry out until spring?

I would suggest that you dig the rhizomes because in a few weeks the larvae will start turning into moths and lay eggs on the dead foliage, rhizomes and everywhere they like.

You can soak the rhizomes in diluted bleach solution but keeping them dry until the spring will slow them down and some may not bloom at all. First I would carefully select the completely healthy ones and then transplant them in pots and winter them in a garage or a similar place where the temperature is not as harsh as outside.

In the spring you can first prepare the sight where you want to keep them and pre-treat with the insecticide I suggested in my previous post or another of your choice. After a week or so transplant them back to the garden.

I would also suggest that you try using nematodes, but they won't be very comfortable if you apply pesticides.

They used to have a chemical called Cygon, I think it was banned, but check the Internet or your local stores, if you find it it's the best to be used with iris borers.

Let me know if I can be of further help.
tex-eng and 49 other General Specialists are ready to help you