ICK!!! I found my very first IRIS BORER!!!

I was weeding and cleaning out my iris beds yesterday and found that some of my rhizomes were squishy. I pulled out stuff and found this anemic (but well fed) nasty worm about an inch and a half long inside one of my rhizomes! Ick, ick, ICK!! I put it in a ziplock and asked my neighbor who confirmed that it is an iris borer.

Here's my question for you all: what is the best thing to do to treat my iris beds to get rid of these nasty things? I think I have them in other beds, too- just not as badly. I did get a ton of satisfaction smashing it but can't smash them all! :) Thanks for your help!!!

Best,
Susie

Oh no - the more experienced iris posters always say to use MERIT.

Unfortunately, Merit granuals only work when applied in the spring so until then it is a hunt and squish approach to kill those nasty critters.

More experienced irisarians please advise if I got it wrong.

Roni

I believe the best thing to do now is to dig up the ones you suspect have borers and squish them. Dumpster or burn the slimy foliage and replant the good parts. In the fall do a cleanup of all dried leaves and debris near the iris, in the spring apply Merit at the optimal time (still not sure exactly when that is!)

According to hybridizers, Merit is best applied the first day AFTER two consecutive days of 72 degrees in the spring. As far as getting rid of them now, hunt and search is the best way. I had an "invasion" of the d#*$ things 3 years ago, and I dug them out and put them on a paper plate in a cardboard box in my yard (they are just too gross to squish -- I admire you, SusieR and Caitlinsgarden). The robins and blue jays helped themselves to the critters, with my blessing. The good news is if you are consistent with your Merit application, you can get rid of them permanently after 3 or 4 years. I haven't found any so far this year (THANK GOD!!)

http://irisgarden.org/borermain.html

Edited to add text: Excellent article on borers which has been posted previously.

This message was edited Jul 9, 2009 3:30 PM

There may have been a misreading of popular instructions for Merit application. The borers
begin to appear after two consecutive days of 70+. I would think the merit should be applied
prior to that time to allow the chemical to migrate thru the roots and the rhizome up into the
leaves, if I understand the process correctly. I have never seen a larva but I have found a
few brown pupae while digging iris beds in late summer before learning of acephate and
other chemicals used especially to kill borers.

I wrote a DG article on iris care that has some info about dealing with borers: http://davesgarden.com/guides/articles/view/832/

I've got a few squishy rhizomes out there now myself, but I'm pretty sure that's due to the wet weather we've had... I had some large-leafed weeds that were shading the rhizomes and keeping them from drying out properly, which definitely added to the problem.

Could I put some Merit on them now? I ordered some ($65 for 2oz of powder!) and would love to put some on when I get it. Would it hurt anything?

It probably won't kill much at this stage as far as the iris borers are concerned... as I understand it, it kills the little borers when they migrate down into the soil (they hatch on the leaves of irises & surrounding plants). Big borers are unaffected, and any early hatching little ones are still up in the leaves at this point.

I use a product like "Grub X" (check for imidacloprid content of at least 0.2%), sprinkled around the clumps when the forsythias start blooming in spring.

Might hurt the bees--be careful with it.

There are some links at the bottom of the article I wrote with pro's and con's of using imidacloprid (including possible issues with bees, although the colony collapse disorder turned out to be something quite different, I believe). As with any pesticide, it's good to make an informed decision and to use no more chemical than needed for adequate control. :-)

What I have heard from Laurie Frazier about Merit is that it is taken up by the plant as growth begins in the early spring and is systemic; when the bitsy borers start to gnaw and chew through the leaves they are poisoned. She says that it has no effect if it is used later.

You're right -- I double checked, and the baby borers don't reach the soil until midsummer. So it's when they're in the leaves that they can be killed.

I spoke with Bayer and they said that, if I used it now, it would still be taken up into the leaves but would not have the potency as if I put it on in early spring. It won't kill the big nasty maggot borers, only what is still in the leaves. I've been pulling out what I can find of the big nasties and killing them (satisfaction!) I just don't know that I am getting them all. I thought that, if I could prevent more from maturing, that would help a little bit. Then I'll hit them in spring. I will be very careful because I don't want to hurt bees. Ants, fine...not bees. :)

Suzie,
I would just find and squish what I can this summer, do a fall and or early spring clean up, and put the merit around every plant early next spring. It will kill the little buggers when they start sucking leaves which is as soon as you need them to die!

As for bees, if it was something that would hurt bees and it was systemic (which means that it is circulated throughout the whole plant like our body circulates blood) it would be in the pollen, etc. also most likely. But I heard that the bee death was caused by a virus from Australia, rather than the grub control product. I had that concern about it also a couple years back.

Saw a leaf lying on the ground and pulled it. Had some rot at the base of the leaf and left
some on the rhizome. Pulled the rhizome and saw a mass of grey mush. Hosed it out and
had this. Probably from a borer.

Reverse side. Normal healthy rz with good roots and the beginning of increases.

I found some borers in two of my iris clumps last year. Totally freaked me out!! I dug all the rhizomes and had to trash many of them. For the remaining ones I bleached, dried and replanted. In the fall (after the first hard freeze) I cleaned my iris beds and trimmed all my iris foliage down to within a few inches of the rhizome (exception: I did not trim back my newly planted rhizomes). I followed Laurie Frazer's invaluable instructions this spring by trimming ALL the over-wintered iris foliage as close to the rhizome as possible. I'm in 5a and did this in early to mid March. Then I sprinkled about a teaspoon of Grub-Ex over each and every clump or single rhizome where there was not yet a clump, and watered in well. The Grub-Ex contains 0.2% of imidacloprid which is the ingredient that kills the borer larvae. As mentioned above it is important to do this BEFORE you have 2 consecutive 70+ degree days. That is when the borer eggs begin to hatch.

Not only have I been borer free this year -- I didn't even have any leaf spot. This has been a very wet year.

Edited to say that products containing imidacloprid are not allowed to be sold in some parts of the U.S. (I believe Long Island, NY is one of them.) I don't use it on my lawn -- only on the bearded iris. I have noticed honey bees in my yard for the first time in many years!


This message was edited Jul 18, 2009 11:43 PM

Imidacloprid in liquid form is not able to be sold in NY. In granular it is.

I had conversations with John at Ensata Gardens about Imidacloprid. He also said it will work now as it is systemic, but does work better early in spring. It will work on whatever insect is chewing on the leaves. In the spring it's baby borers, and they are killed more easily than the large ones.

Grub X is much cheaper Suzie, and should work well.

I was concerned about the bees too, Lucy, and that's where John Coble and I got into a big discussion. But as he says the granular is systemic, and will only hurt what chews or sucks on the plants, and bees are much more attracted to other flowers than irises. I will be very sure not to allow Imidacloprid to get around my nepetas as they are just swarming with bees. The liquid form, sprayed on, would be much more hazardous, and I'm sure that's why it's banned in NY.

This message was edited Jul 18, 2009 11:23 PM

I dug up a big clump of Lousiana iris 'Black Gamecock' this weekend and found that it was infested with borers. II didn't know La iris could get borers. I grow mostly siberian iris and have very few TB iris so I never encountered this problem before. Most of the clump was relegated to the trash heap and I saved only a few rhizomes that were borer free. I put them in pots temporarily and will replant them in the fall after another thorough inspection to detect any borers I could have missed. Borers are disgusting, some were 2 inches long and as big around as a pencil eraser! Ugh!

Don't worry--they can get bigger than that. Note any iris can get borer--check other irises regularly, but maybe the moths just noticed your garden.

Any of the irses can get borers. They are uncommon in siberians and Japanese, more common in Louisianas, and pseudacorus. I think, I don't know for sure, but I am guessing it's due to the size of the rhizome in the LAs and pseudacorus being a little larger.

It's not so well known that the LAs get borers, as the borers are an eastern and middle of the country thing, I don't think they are found in Louisiana, where the majority of the LAs are of course grown.

Really good cleanup of the leaves in fall, and Grub X in spring should solve the problem in the LAs.

Lucy and I cross posted, but once again we agree :). That must mean I'm learning something about irises if Lucy and I have the same answer.

Don't know everything--what's a siberian?

Isn't that a person who hails from Siberia?

Or from Sibiricae, LOL. Never could figure that one out.

You're a funny one Lucy!

I used some Bayer tree and shrub stuff with Merit in it today mixed with water and watered all of my beds. I pulled out the nasties before watering but forgot to do it on one bed and a big nasty came up so I picked him out and squished him on the driveway. Ahhh...satisfaction! As I had already watered this bed with the chemicals, I didn't go through it and pull everything yucky out but I will do that in a day or two.

IrisMA- thanks for the visual- NOT! :) How big can they get? Most of the ones I've found are the size Frahnzone5 was talking about. Then again, maybe ours are related because we aren't too far from each other. I'm now picturing these nasty big iris maggots as big as a man's thick finger and four inches long. If you get them that big in MA, I guess I'll stay here in IL. Ick, Ick, Ick!

I can't decide which I hate more- those tiny ants with their white plethora of eggs or these nasty iris borers. At least the ants don't usually kill my flowers!

They don't reach 4" but I am sure that they would like to.

Susie, I just pulled a pot out of the nursery today, and noticed some ants running around. I pulled the phlox out of the pot, and it had a ton of those ants with the white eggs, you're right ick, ick, ick. I have never seen a borer, though, (yet).

I pulled all the flowers out of the pots to check for more ants, and didn't find any. Thank gosh I didn't sell that one to anyone. Now I have to spray all my pots.

This link mentions a biologic control using a nematode that kills the borer in the larval stage http://www.entomology.wisc.edu/mbcn/land504.html. I found a huge borer myself and hurled it into the street to be eaten by the birds or squished by a car! I found more and doused them with bleach and ground them up in the garbage disposal followed by more bleach down the drain. They are really gross and it wouldn't be so bad if they produced a pretty moth or butterfly but the adult moth is gross too!

Here is another site with a chemical that is used to repel the borer rather than kill it. Five years of research have shone it to be effective, http://www.gardenshield.com/; Another site that discusses the use of the deterrant http://www.irisgarden.org/boreralternatives.html;

Ridgebax,

Thanks for the info! You've reminded me that I have to pick up the Merit I ordered. I passionately HATE these things! You are braver than I - I wouldn't put them in my garbage disposal. I get too much satisfaction cutting them in half with a hand trowel and leaving them in the driveway for bird snacks!

I am still amazed at the way they've totally decimated some of my iris beds. I know that I can't plant any new ones for up to a year (or so I think) so I'll have to treat in the spring and then plant again next fall. I don't want to give these big nasties new and expensive snacks!

wow. i just dug up my whole iris bed and found borers all over the place. gives me the heebies AND jeebies. i knew something wasn't right out there... thank you everyone for the valuable information in this post!