General Discussion:

iris bore or disease

Messages posted to thread:

Suzanne12-Aug-03 11:51 AM EST 5   
Susan13-Aug-03 01:54 PM EST 6a   
ginny14-Aug-03 01:59 PM EST 2b   
Susan16-Aug-03 07:01 AM EST 6a   
Suzanne17-Aug-03 07:32 PM EST 5   
Suzanne22-Aug-03 05:30 PM EST 5   

Subject: iris bore or disease
From: Suzanne
Zone: 5
Date: 12-Aug-03 11:51 AM EST

I have many iris, and the leaves are brown, with many looking dead.I have been told that iris bore is on the increase, and I plan on digging mine up to see what is going on. I am wondering if I need to remove the surrounding soil. I plan on separating tubers, dusting with sulphur, and replanting the healthy ones. Is there anything else I should do? Thanks for any help.

Subject: RE: iris bore or disease
From: Susan
Zone: 6a
Date: 13-Aug-03 01:54 PM EST

If it is iris borer, you should be able to see fat, white grub/caterpiller things inside the rhizomes by now and the rhizomes will be mushy, smelly and rotting.

The iris borer is the caterpiller stage of a moth. The moths emerge in September/October and lay eggs on dead foliage. The eggs overwinter on the foliage and hatch in the spring and begin feeding on the new leaves. The best way to control it is to not allow the dead foliage to remain over the winter - to eliminate overwintering sites for the eggs.

Since the caterpillars have likely not made the transition to moths yet, dig up the irises, check the rhizomes carefully and discard any that have borers (to reduce the population of moths that will lay the eggs...), replant the healthy rhizomes. After frost kills the remaining foliage, remove all the dead foliage - which should remove any eggs that might have been laid by any surviving moths. In March, do another check to clean up any foliage you might have missed in the fall.

Subject: RE: iris bore or disease
From: ginny
Zone: 2b
Date: 14-Aug-03 01:59 PM EST


Zone 5, maybe TO or Ottawa. Anyway, your iris borers will have eaten their way down your leaves, into and out of your rhizome and pupated by now - in the soil. So.... the best thing to do is to replant in a diff. spot if you can.

What I would do, is dig up your iris. Cut them back. Clean up all brown leaves, remove all spent stalks. Look carefully at each rhz. to see if you have an exit hole where the #$%^& borer has gone into the soil to pupate. If rhz. are rotted & smelly, cut them back till you get to the clean white (like an uncooked potato) part. Sometimes I use a teaspoon for this. Submerge each entire plant in a 10:1 mixture of water & javex (chlorox if you are in the US) for minimum 30 mins. Then wash to get rid of javex and rub ajax/comet/bon ami on each rhz. cut. Let dry for a day or two (form a callus) and then replant. In the meantime rake over where your iris were - not dig over, you don't want to bury the pupa- and soak with same javex solution. And leave that area for the winter. Sounds very involved but borer is a disaster in an iris patch.

Hope you get this when your power goes back on. Good luck.

Cheers Ginny in Manitoba, life member of Cdn Iris Society

Subject: RE: iris bore or disease
From: Susan
Zone: 6a
Date: 16-Aug-03 07:01 AM EST

Ginny - the pupae in the soil do not harm the iris rhizomes and are not a reason for moving the iris bed to a different location. If there is a lot of bacterial soft rot accompanying the borer damage, that might be a reason to move the irises but the presence of borers/pupae and moths do not require you to move the irises. Only the growing larvae/caterpiller damages the rhizome (and leaves as they eat their way into the rhizome...) The key part of controlling the problem then is to eliminate the eggs that will hatch into next summer's borers. Cleaning up (removing)this fall and next spring all the dead leaves where the moths lay the eggs is the number one thing to do. Digging up and discarding the borer infested rhizomes will reduce the moth population (and hence reduce the number of eggs to be concerned about....) if it is done early enough to catch the larvae before they pupate. Disinfecting the rhizomes is a good idea to control bacterial soft rot but that may not always be present. If there is not a lot of rot and the soil is well drained and fairly dry, it can be quite safe to replant in the same spot.

Subject: RE: iris bore or disease
From: Suzanne
Zone: 5
Date: 17-Aug-03 07:32 PM EST

Susan and Ginny, Thanks so much for all the info--I am going to print this off, as I have several friends also having the same problem.I appreciate your time. S.A.

Subject: RE: iris bore or disease
From: Suzanne
Zone: 5
Date: 22-Aug-03 05:30 PM EST

I just wanted to report on my iris digging--not nearly as bad as I thought. I couldn't find any grubs, smell or rot, just many dying leaves with dark brown spots on them. I think it has been 5-6 years since they were divided, and the live tubours seemed smaller than the older ones, so perhaps this will rejuvenate them. To be safe, I also put into javex mixture even if not necessary, since I want them to come back to previous glory. Great idea to use Ajax--cheap treatment.How often do the Iris Society recommend division? THanks for getting me moving on the digging--before anything got hatching.

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