iris borers in the ground ?

Well I just had my first terrible case of iris borer. I know what to do for the iris plant but my question is.....can I treat the ground with anything to make sure the borer is gone before I plant more irises there ?
These irises had grown together so that I no longer know which was which. My intention was to remove them totally and plant 4 new ones in that area. Now I'm kind of affraid to plant the new ones in that spot.
Any advice ?

The brown borer pupae will be in the ground in the fall. If you can smash them it will help. At this time the larvae will be in the lower leaves & rhizomes. Check for them as you weed & you can destroy many of them now.

You may try Bayer Merit in the granular form. It's active ingredient is
imidacloprid which is supposed to be a systemic pesticide. It is absorbed
thru the roots to the leaves rather than absorbed directly into the leaves
as acephate would be thru spraying. I could not find any reference to
iris borers on the bayer website but it kills grubs and sucking/chewing
critters. An iris lady, laurief, brought this to my attention so I assume
she used it for borers. You may want to d-mail her directly. Hope this
helps.

This message was edited Jul 15, 2008 5:23 PM

You would have to use the merit in the early spring. Once the borers go into the ground, there is no more damage to the plants this year, I believe. They will pupate and then sometime in the fall turn into a moth and fly about laying eggs for next spring, which is when they hatch and start to attack the leaves. I think the merit is really the only defense against borers once you get them; this is the first spring I have used it. The last few years without it were a nightmare!

Thank you both for your help. I really appreciate you input.

IrisMA, I did actually see alot of the stinkin' things as I was working and was hoping that it was early enough that they hadn't made it to the ground yet.

Oldgardenrose, I appreciate the mention of a possible pesticide type solution also. I work full time (as I'm sure most everyone else does too) and have no time to be playing around with these pest.

I think I have convinced myself to just automatically treat them in advance next year too.

Hi Caitlinsgarden, you were typing same time I was. I was wondering how that cycle went. Thanks.

Merit (imidacloprid) won't help this late in the season. It is only lethal to newly hatched borers in early spring. Right now your best bet is to seek and destroy as many as you can find in the iris fans and rhizomes. It is possible, however, to miss some in ground as they can migrate from rz to rz underground while they are still feeding. The only way to catch any that might be in your soil is to use a fine screen to screen all of the soil within several feet of your irises.

Laurie

Does sulfur do any good? Thought I read that somewhere...

Not that I know of.

Don't mean to butt into you ladies' chat but I rechecked the Bayer Merit page
and found google had added "controlling the iris borer with systemic pesticides".
All you wanted to know about borers and were afraid to ask. If google is your
primary browser go to Bayer Merit Pesticides. If IE use www.irisgarden.org/
pesticides. I use google which is much easier, especially if I am not completely
certain of the exact syntax. Info was apparently added on the 13th.

Another buttin--sulphur is used to increase the acidity of soil in cases where
the ph is leaning toward alkalinity. Good for turning hydrangeas blue from
pink--not good for iris unless you really need it.

Oh my gosh ! you people are soo great ! Thank you soo much for the information. As I said before I do not have enough time to research all this on my own. Dave's Garden is the PLACE TO BE !!!!!