Discouraging amount of work

I am reconsidering my greedy aquisition of irises...Walking in my garden lately has been sooooo discouraging. One clump after another of irises is showing the dismaying evidence of iris borer attack. Almost every one over 1 year old will need to be dug, de-borered, divided, and replanted (in fresh soil if I can find some that isn't under the domination of quack grass.) Then I have to make sure the diseased foliage is all permanantly disposed of...

Unlike daylilies, which just sit there uncomplainingly, year after year...And irises need this attention at the wrong time of year, just when I am ready to go on a gardening vacation.

Has anyone else battled this problem without wanting to dump them all?

Borers are easily controlled if you just apply Merit early in the season just as irises are breaking winter dormancy and starting spring growth. If you don't address the problem until this late in the season, however, dealing with borers can be an overwhelming chore.

Get the jump on borers next spring, and you won't be wanting to dump your irises next July.

Laurie

I guess I am going to have to choose between irises and non-use of pesticides?
I have been pretty much of a purist on that point till now...

Caitlin, when the iris bloom in the spring, that's when you decide you're glad to have kept on another year. I dug an entire flower bed, but got rid of the quackgrass. I took a lot of advice and got the poisons I needed to battle the borer. I haven't been diligent enough, because I see a lot of streaks again. If you dig, find someone to give most of them to and just replant a few for your pleasure.

That's the only way to control them? Does everyone use it? Yeah, I don't want to give up on irises.

I have real old iris from my Mom. They get borers, but not too bad. One is Quaker Lady. The other is a prettier version and has a nice scent. I've almost lost iris before I resorted to poison.

Do you use "merit" also?

I bought the Bayer granules with an ingredient that started with an I. I also already had liquid malathion. (sp?) I bought a sprayer for it at Walmart. I also dig and soak in water so the borers float. Then I snip them with scissors. I added a little bleach to the water for those I gave away this morn. Only one borer came out of a huge clump that hasn't been divided for a few years.

I didn't spray when I lived in Ont. (borer country). I walked the iris rows with my AM coffee.. Every time I saw a leaf with a bite in it I would slide my fingers down the leaf and usually squash the borer in the leaf.

Would find the odd borer when digging in the fall but only 2 or 3.

Secret of borers is keep your iris clean. Clean up in the fall Take all dead leaves away. Not compost, in the garbage.
inanda

I do that, and I try to feel them in the leaves, but haven't had any luck yet. I've never found one in the soil.

The borer will rarely be found right in the soil. He quickly turns into a pupa when he bores thru the bottom of the rhizome. A pupa is a brown and inert capsule, and can easily be missed as just part of the soil.
Found one nasty borer today in the process of pupating. Thankfully he won't complete the jobr.
Laetitia

I squish every brown little one I find, even tho I don't know exactly what they are. They don't look benificial. I squish all grubs too. Sorry to those who feel nature must live.

I can do the AM stroll with a cup of coffee!
What I am finding now as I dig the iris are shredded and slimy inner leaves, that you can't even see from the outside. Where are these bites, and what do they look like?

You 'walk your iris' starting early in the spring. By now the borer will be on its second cycle. I'll have to dig around and see if I have a picture of a borer entry on a leaf. Dont think so though. If you see a little 'nip' on the side of a leaf, just go to the bottom of that leaf, between your fingers and run ypur fingers up the leaf. With luck you'll feel as very satisfying squish.

Thank you, for any and all advice. So the only thing to do this season is dig and destroy and replant in a different spot? And then early next spring look for evidence of new borers and squish? I see I will have to study the "pest" section of my new iris books. Arrrgh. Just discovered something is destroying my lilies also...But that's another forum.

I can understand your reluctance to use toxic chemicals in your garden. I hate using them myself and will only do so under extreme circumstances. Borers are one such extreme circumstance. The only reason I use Merit is because the active ingredient, imidacloprid, is the same active ingredient used in Advantage Pet Flea Control products. If it's safe enough to be applied directly to an animal's skin without deleterious effects, I figure it's about as safe as any chemical is likely to be in the garden. Neither Merit nor any other chemical or soap treatment will eliminate borers at this time of year, however, because they are too large and resistent. In order for Merit to be effective, it must be applied early in the spring when the borer larvae are newly hatched, tiny, and still vulnerable to pesticide.

In order to manage borers effectively, you need to understand their life cycle. Borer eggs are laid on iris foliage in the fall and overwinter there. In the spring, egg hatching is triggered when temps reach 70 degrees. The hatchling borer larva bores into a green iris leaf, where it will start to feed and continue to feed as it works its way down the interior of the leaf to the rhizome over a matter of weeks, getting larger and more resistent to pesticides as it feeds.

Eventually it reaches the rhizome where it continues to feed until mid-summer. If it runs out of food in the original rhizome, it may migrate to another nearby rhizome through the soil and continue to feed. When it is ready to pupate, it leaves the rhizome and creates a small, dark brown capsule near the iris and within the top 4" of soil in which to pupate for the rest of the summer.

In late summer-early fall, the adult borer moth emerges from the pupal capsule and the soil and lays eggs on iris foliage to begin the cycle all over again. Because the adult form of the iris borer is a moth, they can easily fly from one garden to the next to lay eggs wherever they please. If you have neighbors with irises that are untreated for borers, chances are that you will have borer populations every year in your own garden. This link will show you pics of the various stages of borer development:

http://www.worldiris.com/public_html/Borer_Sequence/Iris_Borer_seq.html

The only way to interrupt the cycle at this time of year is to dig the irises out of the ground, wash and do a bleach solution soak of the rhizomes, and inspect them for signs of borer activity. If you find holes in the rhizomes, either cut the borer out of the hole with a sharp knife or poke around in the hole with something pointed to try to kill the larva inside the rz.

If the larvae have already left the rzs to pupate in the surrounding soil, the damage to your irises is already done for this year, so now you just have to treat for secondary bacterial infections in your plants. Don't worry about the pupae in your soil. You can take care of them this fall and again early next spring (before temps reach 70 degrees) with a thorough garden clean up to remove the old iris foliage with next year's borer eggs. Early next spring, apply an appropriate pesticide like Merit before temps reach 70 degrees so the plants can uptake the chemical and be toxic to the hatchling borers as soon as they begin to feed.

Don't give up. I know this all seems very discouraging right now, but borers really can be managed with relative ease through the timely application of Merit early in the spring. For now, just do what you have to in order to treat your infection and hope that enough of your rhizomes survive to be able to rebuild their clumps.

Laurie

Laurie, thank you for this wonderfully detailed expose~ of the life of the iris borer.
Are all of the leaves that are on the plant now considered "old" foilage next spring?
Will they all be brown and easy to discern from new growth in the spring?
I have to confess - I am a terrible housekeeper, both in the house and in the garden...Will have to change my habits I see...
Thank you again,
Sharon

Sharon,

I assume that iris foliage dies back in your zone over the winter, so next spring before temps warm up, remove and trash or burn (do NOT compost) all old iris foliage. If, however, your iris foliage remains green all winter, cut it back to the ground in early spring before new growth starts and let the irises grow all fresh (borer egg-free) foliage. Also, clean up all other weeds and plant debris from around your irises (it's possible borer moths may lay eggs on plant material other than iris leaves -- I'm just not sure). If you get all of this old stuff cleaned up before temps warm in the spring, you'll eliminate the majority of the borer eggs before they even have a chance to hatch. It probably won't be enough to eliminate borers completely, but it'll sure give you a good head start.

Laurie

That I can do! Now, on to the iris forum....
Laurie, I want to send you an original watercolor just because of gratitude for all of your advice. Please tell me your favorite color family and I will send you one some day as the inspiration moves me...
Sharon

Sharon,

You are so sweet! You know it's not necessary to reward me for opening my big mouth and talking about irises (or even iris borers). ;-) But I sure would never turn down a piece of original art! The palette is open around here. My walls are white, carpet is grey, window valances are shades of teal green, dusty rose, and dusty mauve (and I mean "dusty" in every sense of the word. LOL).

Laurie

Hi Laurie, I might seem to be especially fond of the "dusty palette" myself!

One fall (I know, too late in the year) I dug up every one of 681 irises and checked each one for iris borers, a few came out in the bleach water and I cut away all the bad parts of the irises, laid them out to dry in the sun and then replanted them, a section at a time, in fresh soil, on slightly raised mounds. It did work out for the best but it's hard to keep up with that job.

It really is very discouraging but I am getting blooms again and won't be so inspired to dig and replant so many at once ever again.

I wish you the best with your irises.

Here is a ''shame on me, but it got away from me,'' picture of borer damage.

I "crunched" a few borers near the bottom of a blade this morning, but they seem to be just into their "burrow into the rhizome stage". I understand what everyone is saying about spring being the time to attack the problem, but aren't they going to destroy everything if I wait till spring? Or will there be less loss if I leave them alone
(except for cutting off the foliage and fall and spring clean-up), then in the spring dose them with merit, if I decide to go that route. I wonder if I am overboard in my dig and destroy mission. I know I wouldn't want to have me for a surgeon!

If you have borers that are actively feeding now, they will continue to consume your irises until they are ready to pupate. Try to smoosh as many as possible while they are still in the leaves, but if you suspect you have them in rhizomes that you want to save, you'll have to dig them up and do surgery. You'll definitely have more loss if you don't do anything now.

Laurie

I only dig and divide the ones where the borer is known to have penetrated the rhizome. If I "pop" it in the leaf, I cut the ugly chewed leaves and allow the plant to generate new foliage. I do not use any control method other than this. I do watch for signs of infection aka rot in the plants where a borer was squished but usually have no other problems. Before shipping, I thoroughly inspect each rhizome and give it a 10% bleach treatment.

Roni

A few other interesting "facts" (or at least things I have read but cannot attest to the accuracy thereof) about iris borers:

Borer larvae are cannibalistic. You won't be likely to find more than one in any particular leaf or rhizome.

Borer moths are active only at night.

Borer moths are poor flyers, so they can't travel long distances between gardens to find irises.

I am learning all kinds of interesting things. So, if one were to replant cleaned irises in new ground away from the present infestation, it would likely prevent a continuation of the problem...I have to re-do my iris beds and make them easy to see and take care of. No more jumbled mixed beds with irises. It seems likely that a fine meshed screen around choice irises would prevent the flying moth from reaching them and laying eggs, but I doubt that is a workable idea. It might work in a pinch though for some special plant. I wonder what is in that "garden shield".

I wouldn't count on it, Sharon. I only read that bit about borer moths being poor flyers in one article, and I'm not sure I believe it. I don't even know how the article qualified "poor flyer". Unless you garden over a couple of hundred acres, I expect a borer moth is more than capable of flying around the average sized garden (or several gardens in the same neighborhood) to lay her eggs.

The Garden Shield stuff was a bitter tasting repellent. They asked me to test it for them when they first started marketing it. I tried it once and never again because it left horrible spotting all over the iris foliage even when used according to label directions. It also required reapplication after every rain or heavy dew, and it wasn't cheap! I don't think it's even being made anymore, though I could be wrong about that.

Caitlinsgarden:
I thought it would be a worthwhile invention to create some kind of tent of fine netting to put over prized iris during the borer moth laying season, however It is only an idea; have too many iris to try it.
Laetitia

I also tried the Garden Shield a few years ago, and like Laurie said, it left spots all over the iris, smelled awful and you had to reapply it after it rained. At 24.99 for two bottles, I could easily go thru a bottle after each rain. I would not bother with it again. I am not even sure it did anything to discourage the borer.
Laetitia

Caitlin,

If you are catching borers still in the leaves, it would be worth it to dig them now, check them all, cut them back and replant somewhere else. Of course, I don't know how many you have.

If I had as many as Laurie, I probably would have to use Merit. Don't even know if you can get it up here.

Keep us posted as to what you end up doing.
inanda

I am finding some of the iris I dig has masses of white (eggs?) near the rhizome. Are these part of the iris borer cycle, or is it another pest? It is similar to others I have observed when I turn over rocks, etc.

For years I have grown the iris that came with our farm with no problems and no attention until they were so crowded they couldn't breathe. I suppose there were a few borers, but it never even came to my attention. But as soon as I started purchasing the more choice varieties iris growing became very iffy.

Most of my original irises grew for years mixed in with my asparagus beds. I still have beds like this and both crops do well together.
As I read more about the iris borer and it's life cycle, I am wondering if the dense
wall of asparagus foliage in the fall somehow makes it harder for the moths to get to the iris. Or the smell repells them. As an experiment I think I will plant some of my newer iris with the asparagus seedlings that pop up everywhere...

I would think your white egg masses belong to some other insect pest, not the borers. Or the white masses might be "shavings" off of the rhizomes themselves as the borers feed. But if you're seeing similar masses under rocks away from irises, they're probably some other insect's eggs.

Interesting observation about the asparagus and the irises. It'll be interesting to see how that works out with your newer irises.

There are definitely irises that are more appealing to borers than others. Just one more reason why I prefer SDBs to TBs. I've never seen borers bother the small SDB rzs.

Laurie

May I suggest -gently- that you soak SOAK the entire rhz. Submerge the entire plant in 10% beach, that is one part bleach to 9 parts water. Soak for at least 30 mins, then rinse well and allow to dry before planting.

That will stop nasties getting in to your garden.
inanda

Small masses?? Might be snail or slug eggs. Used to find them when living in PNW.

Thanks. Just got 2 containers of bleach from the store!

I have been doing just that, except not for 30 minutes.

Laurie, the initials used for the iris are not any I know. I did find out PC was Pacific Coast. What are your initials?

Caitlin, my worst borer infestation is in the clumps I didn't get dug and divided last year. Like you said, I put mine in an easier place to spray.

Most of mine are under walnut trees.

MDB=miniature dwarf bearded
SDB=standard dwarf bearded
IB=intermediate bearded
BB=border bearded
MTB=miniature tall bearded
TB=tall bearded
Sib-Siberian
JI or JA=Japanese
LA=Louisiana
SPU=Spuria
AB=Arilbred
PCI or PCN= Pacific Coast

LOL, I have the tall bearded and I couldn't figure it out. Oh boy!