first time here, first time borer!

16 years ago

hello everyone!

i have had irises for about 6 years. last year, my german (?) irises looked horrible and didn;t bloom. about 2 feet from those i have an unid'd purple iris that i transplanted from a OLD homestead area. these are bloom and multiply like crazy.

this year, again, my german irises keep "rotting." i had no knowledge about borers before, and in a freak accident sort of way, i learned yesterday. i was pulling the dead stuff when a piece of rhizome came with it with one of those juicy fat borers in the rhizome. i have found 2 with just pulling dead stuff. the remainder keep trying to grow more foliage throughout this spring/summer.

what i find strange is they have not bothered my purple irises which are in a huge clump. both these iris types get treated the same by me: clean up dead stuff in spring, or as soon as i can. from now on, i will be doing it after a hard frost! correct?

i have found info that beneficial nematodes will attack borers. has anyone had experience using this? i did not find nematode use in the search for borers. i would like to stay with organic means.

thanks!

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Comments (17)

ritaotay
16 years ago
I'm not a pro but here's what I do when I find those dirty buggers in my iris beds. First I dig them all up.... After I have them all out of the ground I put them in a tub of soapy water and hand wash all the bugs and dirt off. Then I take them to the other side of the yard and rinse them off, really good, with the hose, I just about drown them with a heavy spray. Then I move them to another part of the yard and while they're drying out I use a spade to 'chop' up the soil and kill any iris borers and/or bugs I see then I level out the bed. While the sun is beating down on the bed I sort out the irises, tossing out the badly damaged ones and cutting off sickly looking leaves... As I clean them I lay the 'fans' flat on the grass, more or less stacking them but with the rhizomes pointing up and far enough apart to let them air dry. That takes me most of the day so I don't re-plant them until the next day but I keep them moist over night by covering them with a well wrung out sheet. The next day I let them dry a bit before planting and when I'm through I water the bed then leave them alone, until they need water again or weeding. LOL I wish you luck, I know what a job it is to re-do a whole bed, I do it every 5 years or so... lol

Rita
fairy_toadmother
Original Author
16 years ago
i am glad i have only a few irises! i was thinking of taking out the purples, if i place my german ones where the purples were, would this be a crop rotation action? would they be far enough from the borers in casae there are any left?
thanks!
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iris_gal
16 years ago
We don't have them but from reading others' posts I understand squishing them in the leaves before they reach the rhizome is possible. Do a 'borer' search on this forum to see if any of those posts are still around.
laurief_gw
16 years ago
Your purple irises don't have borers because some iris cultivars, for whatever reason, are less appetizing to borers than others. A "crop rotation" won't help reduce borer activity. Once the larva has had its fill, it leaves the rz and pupates in the surrounding soil. In late summer-fall, the mature borer moth emerges and lays eggs on old iris foliage. If the foliage on which it wants to lay its eggs has moved 2' away, it'll simply fly over to it and lay its eggs there.

In late fall and again in very early spring before temps rise to 70 degrees (borer hatching temp), do very thorough cleanups of all dead, dying, and diseased iris foliage as well as weeds, leaves, and other plant debris from around your irises. Burn or trash the cleanings. Do NOT compost. That'll eliminate the majority of borer eggs.

Next spring, keep an eye on your irises for signs of borer activity: chewed leaf edges (particularly along the outer edges of the inner leaves) and watery looking streaks running down the leaves. If you find such damage, run each leaf between your thumb and forefinger, starting from the bottom, sqeezing the leaf all the way to the top. If there's a borer in the leaf, you will squish it as you work your way up the leaf.

Right now you need to dig up the infested clumps, inspect each rhizome carefully, and use a sharp knife to cut out and destroy any borer larva you find, along with any rotted rhizome flesh. Soak the rzs in a solution of 1 part bleach to 9 parts water (or is that inorganic?) for 20 mins, then rinse in clear water. Allow the rzs to dry in a protected spot for several days before replanting.

In the meantime and if your soil texture allows it, consider screening your soil to try to find and destroy any borer pupae in the soil surrounding your infested clumps. If they are present, they will most likely be in the top 4" of soil within a 1' radius around the clumps.

I have read that nematodes might be useful but that they need to be applied under just the right temperature and climatic conditions to be effective.

The link below will take you to a page that has pics of three stages of the borer life cycle: larva, pupa, moth.

Good luck with your borer battle.

Laurie

Here is a link that might be useful: iris borer pictorial
fairy_toadmother
Original Author
16 years ago
iris gal, i think it is too late for the squishing, though i remember reading that tip. most of the foliage is gone, i do have some new growth. should i do this on the new growth that started withing the last 2-3 weeks? the borers i found were very "healthy" looking, fat and very pinkish-brown, nearly 2" long.

laurieF- i wondered about "discriminating" borers :) and thnk you for letting me know that moving the affected ones will not help but be found anyway. ihope to do the bleach thing organic/inorganic or not. it will be dry before going back into the soil. if irises get more sun, will they be less susceptible to borers? not likely, i suppose, but i read that unhealthy plants are more affected/attractive. also, thank you for the link, i culdn't find any pics of the borer moths! it was driving me crazy! the 4" and 1' is extremely helpful as well, i never even thought of screening or how far they would travel.

thanks again, everyone!
njiris
16 years ago
Borers seem to prefer the modern more juicy cultivars. Also the ones with no pbf!
I have just dug up hundreds of iris rhizomes at Presby Iris Garden and it is amazing how certain rows of cultivars are infested, right next to other rows of tightly packed rhizomes with no sign of infestation. I can truly say without any doubt that iris with no pbf are preferred by the borer.
Maybe pbf doesn't taste good?
Laetitia
fairy_toadmother
Original Author
16 years ago
forgive my ignorance, please. what is pbf?
techsupport8
16 years ago
pbf = purple based foliage. Right near where the rhizome and the foliage meet is purple colored on pbf plants.

Regarding Iris borers, I have found them to be cannabalistic - never more than one per rhizome.
zintal
16 years ago
Most of the time I am an organic gardner but not over iris borers. When I spot them I dig up the clump and cut out all rotted areas and trim the leaves to healthy parts and fungicide them. It postpones bloom for a year with some irises but not others. I do not dig up all the clumps not showing a problem however for most seem healthy and usually I do not get the borers back again for many years.

What is bothering me this year is slugs and snails all over the iris. Never had that problem before and that might be from rain, rain, rain so I stomp, stomp, stomp the offenders.
fairy_toadmother
Original Author
16 years ago
i'll take some of that rain! hope some friendly toads come visiting to take care of those slimy things.

thanks for explaining pbf. duh, ftm!!
nebrjean1027
16 years ago
Some people in our area believe (and swear by) burning the iris leaves (just singe the leaves down to the rhizome) and the ground around the iris in early March to kill the eggs. Seems to work fairly well. There was an article in Tall Talk by Henry and Opal Wulf last year.
fairy_toadmother
Original Author
16 years ago
now, that is interesting. i am sure it kills any overwintering eggs. however, mine is close to a wooden privacy fence so not a good idea in this situation. i will certainly file it away in my memory :) thanks!
katob Z6ish, NE Pa
16 years ago
I'm glad you asked about the pdf! :)

I was just de-boring my mom's iris this weekend. They were pretty far along. I take the garden shears and cut back the fans until they are clean and healthy looking (no muck or brown). For the advanced cases I end up cutting down into the rhizome up until I find the culprit.

I hate borers. Most other pests will eat their fill and move on, borers have to kill the whole plant... and the rotten roots STINK.
fairy_toadmother
Original Author
16 years ago
i have to admit, i still haven't taken care of my iris. please don't shoot me- i work afternoons and do not get up early. also, i just tranplanted a passionflower cutting in this area which is why i was cleaning up the bad foliage and found the brats!

i will certainly be looking for pbf in the future! at least it took a few years for them to find me.
mad_gallica (z5 Eastern NY)
16 years ago
Laetitia, could you post a list of pbf iris? Just what you remember from Presby is fine.

The ones I have are Quaker Lady, President Pilkingdon, Wabash, Thisbe, and Mme. Henri Cayeux. They do honestly seem to be more borer resistant.

I'd like to try beneficial nematodes next spring. Any ideas where to find them?
laurief_gw
16 years ago
There are two PBF lists you may want to check out. The first is on my website, and the other is on the old HIPS site linked below.

Laurie

Here is a link that might be useful: HIPS PBF list
njiris
16 years ago
Gee, I don't remember all the ones at Presby that had pbf. Some of the older ones that we were digging up were FRYAR's GLORY, BY MORRISON, NOKOMIS, KHEDIVE, SANS SOUCI, SAMBUCINA, JACQUESIANA, SHERWIN WRIGHT, MME HENRI CAYEUX,CORONATION, CINNABAR, DOLLY MADISON, FRECKLES (the old one), BLUE MOUSE. Iris you rarely see anywheres. I can't remember any more, but Laurie has a great list.
Laetitia

first time here, first time borer!

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