Lost Most Beard Iris Rhizomes this Year

9 years ago

I have two beds of tall beard iris. They are mature beds and crowded with rhizomes. They are over-due for digging and dividing.

But this spring, they did not come up much and did not bloom. The iris borers got them.

Since BIs are so relatively trouble free, I've not paid much attention over the past ten years. Never any problems. I believe I saw some sawdust type substance last year and that could be iris borers. Over the winter, I did not rake the mulch and leaves.

Anyhow, I just dug out the remaining iris rhizomes from the beds. Whatever remains are the very young shoots from the damaged rhizomes. Most of the rhizome roots are gone. I cut away the rotten part, soak the rhizomes in bleach. I've planted most of them and will replant the rest.

This spring, I think the borers may come back and I plan to spray. I believe after the rhizomes grow stronger and I clean the beds regularly, I may not need to spray next year. For about nine years, the BIs did very well.

The new plants may not bloom well, but they should be able to catch up very quickly.

Featured Answer

drmbear Cherry

9 years ago

Instead of "spraying," consider applying nematodes that will attack the borers, applied right around the time temperatures range at or above 50 degrees F. The cost really isn't all that different than the chemical alternatives. The most common thing recommended for iris borers is Merit, a systemmic pesticide whick gets into the plant tissue. It is the systemmics that are causing the biggest problems for bees from what I understand. Iris are a flowering plant, and bees will be visiting the flowers - can't help themselves. I like the idea of using something that targets specifically the culprit - and nematodes do that.

In my research for dealing with my borer problem, another thing to ensure is to remove all iris leaves and debris from the yard, and trim all the flags down to 4 to 6 inches right around this time of year. Apparently, borer eggs are laid on the tips of the flags in late summer, so trimming them and removing them from your yard should help reduce or eliminate nexts year's invasion. It's what I'm hoping anyway.

Here's info sources:

A summary of the study on the effectiveness of parasitic nematodes appeared in the Bulletin of the American Iris Society, series number 309, (April 1998), pages 35 to 37. Another version of the article can be found on the internet at www.agnr.umd.edu/users/ipmnet/98-2nmn2.htm A definitive article on parasitic nematodes by Randy Gaugler, Department of Entomology, Rutgers University, complete with color photos and a source list can be found on the internet at www.nysaes.cornell.edu/ent/biocontrol/pathogens/nematodes.html Dr. Parwinder Grewal, an entomologist at The Ohio State University, produced nematode reference center on the internet at www2.oardc.ohio-state.edu/nematodes/default.htm

Parasitic nematodes are microscopic roundworms that feed on insects and have used successfully control insect pests. In a study reported in the April 1998, Bulletin of the American Iris Society, parasitic nematodes were shown to equal or more effective than Cygon 2-E or Merit. Cygon and imidacloprid (Marathon) both showed an reduction in borers of 87% while nematode Steinernema carpocapsae had a 100% reduction and nematode Heterorhabditis bacteriophora gave an 87% reduction.

I hope this helps!

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Comments (12)

iris_gal
9 years ago
Those borers sound like a nightmare. This article helped me understand why it's so hard to be rid of them.

Here is a link that might be useful: borers' life cycle
Nancy
9 years ago
I'm so sorry you've had this problem. I feel very fortunate that I've never had iris borers (knock on wood!). I do try to clean up my iris beds in late fall & early spring, but as many iris as I have, I would have a problem. I hope your iris recover quickly.
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Do a search for iris borer. There's also a current discussion, one of the top few on the list about what to do with these things. 'Lost Most Beard Iris Rhizomes this Year' is the title of the discussion. I hate them. If it were me, and I I knew the borers were active in the rhizomes, I would dig and cut back flags to 3 or 4 inches. Clean ALL iris plant matter from the bed and dispose of it. Soak the rhizomes in a bleach solution - there are directions for this online - most say to soak them at least a day since these things are hard to kill. From most of the recommendations I've seen, it is recommended that every fall, even when not digging them, it is best to cut back and dispose of the flags since the eggs for these things are laid in summer on the tips of the leaves. And remove all old plant debris from the beds. The pesticide option you will see the most is for Merit or a similar systemmic product. I hate this option because the pesticide is absorbed into the plant tissue (and actually any plant tissue it comes in contact with). I grow my iris close to where I grow things to eat, fruit trees, and more. Also, iris are flowering plants, and any time you are flowering you attract bees. It is the systemmic pesticides that have been identified as one of the most significant killer of bees. The amazing thing is that at a similar price point, beneficial nematodes can be applied next spring when temperatures get to about 50 degrees F, the same time those borers get into motion, and they will kill them all far more effectively than the systemmic. I provided a little more info in the other thread. My iris are starting to recover over the last year, but certainly not so many nice blooms this year because I was starting with such small pieces of rhizomes when I went through my treatment. I'm hoping by next spring and summer things will start looking nice again. Good luck. Here is a link that might be useful: Lost Most Beard Iris Rhizomes This Year
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RedSun (Zone 6, NJ)
Original Author
9 years ago
I just replanted, actually in larger beds. It is just that the plans are smaller and some won't bloom next year. I even gave away some to friends.

I think I could have saved more rhizomes had I dug them in spring or early summer. But I would not have new beds for the roots.
RedSun (Zone 6, NJ)
Original Author
9 years ago
Do you folks know if the Iris borers are the same buggers as the pumpkin vine borers? I also lost most of my kabocha pumpkins due to the vine borers. Regular haloween pumpkins did ok even with the borer damage.
drmbear Cherry
9 years ago
Not the same critter!
RedSun (Zone 6, NJ)
Original Author
9 years ago
Both are gross fat buggers.

I only saw one iris borer after I dug. Most of them already escaped.

I killed a lot of the pumpkin vine borers. Helped a little, but not enough.

I figure the same chemical, Merit, can be used on the vine borers too?
drmbear Cherry
9 years ago
If you use Merit for squash vine borers, realize that it will be in the squash you want to eat as well. It is a systemmic pesticide that gets into the plant tissue - that is why it is so harmful to bees. Most of the systemmics have warnings for you not to apply it around food crops, but it seems just as harmful to apply it around flowers, since they are visited by things we want in the yard. I grow daylillies in areas close to where I grow iris, and it is not unusual for me to pick daylilly blossoms to eat in the yard or add to a salad. If I use a systemmic to eliminate iris borers, there is a possibility it could get into my daylillies. I also have some fruit trees in areas where I have some iris growing - I'm not really interested in getting that stuff into my fruit trees - something that could be devastating to bees and to me. Like I said, the nematodes work just as well or better, and it seems at a similar price point, so why choose something so harmful. And please do not use Merit on things you want to eat. Check out this list of facts about Merit:

http://www.flora.org/healthyottawa/merit-pesticide-insecticide-grub.htm
KarenPA_6b
9 years ago
where can I buy these nematodes, drmbear? I also have problems with borers and rose midges.
drmbear Cherry
9 years ago
Just search "Beneficial nematodes iris borer" and look for some good sources. Some of the articles about how this works provide sources as well. I'm buying along about April.
mad_gallica (z5 Eastern NY)
9 years ago
Where are you managing to get affordable nematodes? I've looked into them for years, but by the time they get here, the price is going to be well over $50. The killer is shipping, since they have to be sent overnight. And it certainly doesn't help that all the sources are on the West Coast.
drmbear Cherry
9 years ago
Arbico Organics seems to have reasonable prices - the shipping for Garden size to VA is a little better than $16.

http://www.arbico-organics.com/

SIZES & COVERAGE RATES
1/2 Garden Size: $16.00
5 million Nematodes -
Treats approx. 1,600 sq. ft.
Garden Size: $29.95
10 million Nematodes -
Treats approx. 3,200 sq. ft.
Farm Size: $68.75
50 million Nematodes -
Treats approx. 1 acre
Small Ranch Size: $198.00
250 million Nematodes -
Treats approx. 5 acres
Large Ranch Size: $379.00
500 million Nematodes -
Treats approx. 10 acres
Grow Organics seems a little higher:

http://www.groworganic.com/

They are also for sale on Amazon and eBay.

I also found:

http://thebeneficialinsectco.com/

http://www.gardensalive.com/ has reasonable prices and shipping at about $10.

http://www.gardeners.com/ has reasonable prices, though they seem to be out right about now (okay since I don't want any until April).

Close to when I am ready to buy in April, I will build a simple spreadsheet to compare prices, quantities, shipping, etc., making sure I am getting the correct recommended types, Steinernema carpocapsae and Heterorhabditis bacteriophora, and find the right deal. I had been growing iris for almost 30 years without a single borer problem until the last year or so, so I am thinking with some good management and cleanup/trimming in the fall, and a treatment at the critical time with nematodes I should be okay for a few years, particularly since I dig and divide about every three years - another opportunity to treat.

Lost Most Beard Iris Rhizomes this Year

drmbear Cherry

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