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iris borer question

Posted by mrtoad 7b NC (My Page) on
Mon, Mar 30, 09 at 16:23

new to iris - a question or three about the dreaded iris borer

what time of year do they appear and what do they look like

do they eat the flag from the inside and move toward the rhizome - and when will the little guy be big enough for me to see

help - a quick lesson, please

mr toad

Follow-Up Postings:

RE: iris borer question

Mr. Toad: here is what I found on one site:

The adults emerge in September and October from the soil and mate. The tiny creamy-white to lavender eggs are deposited in small clusters on dead leaves; for this reason is it particularly important to remove such dead leaves in the fall. A single moth lays over a thousand eggs. Hatching occurs the following spring, in May in the northernmost range. The minuscule, young larvae feed on tender new leaves, causing notches and the sap to run. They eat their way downward, until they find both food and shelter inside the rhizome, where they gorge themselves on the flesh until early August, and enlarge to 4-5 cm. The injuries caused by the borers greatly increase susceptibility to bacterial rot, and rotting leaves is another symptom of borer infestation. The full-sized larvae leave the rhizomes, crawling through the top 5 cm of the soil for several meters. Still underground, the larvae metamorphose into non-feeding, chestnut brown pupae that twitch when touched. These pupae are found all over gardens where irises are grown when gardeners dig, plant and cultivate the soil. They should be destroyed manually, or placed on a bird feeder as a special treat for insectivorous birds. The 4 cm, dark grey, nocturnal moths emerge from the pupal cases in September, completing the yearly cycle.

RE: iris borer question

Thank you for posting this. I am so relieved to read this.

I have never seen a borer and here we leave the old foliage on over winter to protect the plants from extreme temperatures and desication. We clean foliage in the spring.

I started cleaning the foliage last weekend and disturbed a brown moth. I was so afraid it was a borer but now know it was the wrong time of year to see the adults.

RE: iris borer question - thanks

shapiro - thanks for your help - this is a great site for the novice -

again thanks, mr toad

RE: iris borer question

Here is a link to my web page. It has photo of a borer, pupa, moth and eggs. The only picture of borer eggs on the net that I know of. How do I know they are borer eggs? I set up a aquarium with 2" of dirt and a iris plant. Then placed several borer pupa in it. It had a screen top. They mated thus the eggs. Had several sets of egg.

Mike G

Here is a link that might be useful: iris borer info

RE: iris borer question - revisited

what time (month, etc.)of year would be the earliest that one could find an "iris borer" on the ground or on the leaf

thanks, mrtoad

and please, do not say, monday at 4:00 p.m. :)

RE: iris borer question

Mr. Toad, I have never found a borer larva anywhere other than inside an iris fan or rhizome. When they hatch, they're tiny, and they immediately start chowing their way into the fan and then down into rhizome, so they disappear from sight quickly. As they eat, they also eat their siblings as they encounter them, and as a result, you'll rarely find more than one or two borers in a rhizome. (Charming critters, eh?)

Borer eggs hatch when the temps hit about 70* F, so I try to get my spring cleanup done before the temps get that warm. Then I burn the dead foliage, laughing maniacally as I do so. (If you cannot burn, throw the debris out - don't compost it!)

While I am NOT a fan of using chemicals in my garden, and I try to find OMRI-certified organic products when possible, I have used Bayer Corporation's Season-Long Grub Control for Lawns - be sure the active ingredient is imidicloprid!!!) with success. I apply about a teaspoon per clump right before a rain (or water it in after applying). I apply this right as the irises really start growing in spring - right around those first 70* F days. After the borers get some size to them this treatment is reported to not be effective, so be sure to get the irises treated early.

I am hoping to get a propane weed torch in the future to try burning the iris debris right in the patch as a control measure. I have read others have used this with success.

Another thing I'd like to experiment with is spraying BT (Bacillis thuringiensis spp.) onto the irises. That is an organic method (HUGE plus for me) and seems logical IF it's applied at the proper time. (It would have to be applied BEFORE the buggers hatch and get into the fan, as BT is not systemic - just a surface spray. So probably several applications in spring.)

Hope this helps!

RE: iris borer question

thank you - so much

mr toad / rdeal

RE: iris borer question-Merit?

Last year I ran across information on the iris borer and the Bayer pesticide, Merit. As borers are rampent here, I would like to treat my new bed, iris planted last year. I originally used Merit on my Ash tree and would like to try it on the iris. What info I need is when, and how.

I am not normally a pesticide person but I believe it's the only way to have tall bearded iris here in the Midwest. I cannot use BT, as I have a seperate butterfly garden. All information is appreciated.

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