You've found the famous Dave's Garden website! Join this friendly global community that shares tips and ideas for home and gardens, along with seeds and plants!
Check out the DG homepage for a brief overview of what you'll find in this gardening mega-site.
Login
If you don't have an account yet, visit the registration page to sign up.
The adult iris borer is a moth. In late August and September, the female moth lays her eggs in clusters on the iris leaves, the base of stalks and other nearby plant debris. The eggs overwinter in the plant material and hatch in April or early May as the new iris leaves are expanding.
The small, young, larvae crawl up onto the new iris leaves and make tiny pinpoint holes as they enter. Once the larvae enter the foliage, they act as leafminers, tunneling to the base of the leaves throughout the spring. This leafmining damage appears as water-soaked, brownish spots and streaks on the leaves. By early to mid-July the larvae reach the soil area and tunnel into the rhizomes.
In the rhizome, the fat-bodied, pink larvae with brown heads grow to be 1-1/2 to 2 inches in length. Their tunneling in the rhizome is particularly damaging to a smaller-rhizomed iris such as Japanese or Siberian iris. A tall, bearded iris, with its larger rhizomes, frequently is able to sustain this damage and still survive.
In late July to early August the iris borer larvae move from the rhizomes into the soil to pupate. Adult brown moths emerge in late August and September to mate, lay eggs and repeat the cycle described above. Usually the main problem with iris borer infestations is the accompanying invasion of bacterial soft rot. Rhizomes infected with bacterial soft rot become slimy, soft and foul smelling. The combination of bacteria and borer can cause rapidly appearing serious injury.
With close, regular inspection of leaves from April through June, iris borer larvae can be easily detected at their telltale chewed damaged spots, leaf discoloration, and other signs such as dark watery appearing marks.
Fall sanitation is very important for iris borer control. Following the first hard frost, remove and destroy old iris leaves, stems, rotted rhizomes and nearby plant debris. This will help to get rid of the overwintering egg stage. Insecticides labeled for iris borer control may also be used in the Spring of the year on new foliage.
Also, check out the web version of this update for several other great photos and the following webpage by Cliff Sadof: Hyperlink The foregoing information was gathered entirely from Purdue University, West Lafayette, Indiana website.
Entries and Updates
Aug 2, 2006
This entry is anecdotal to my initial comments. I will be adding pictures of my own of iris borers and their resulting damage as time and circumstances permit. As I write the current temperature is 91F with a heat index value of 105-108F, so this gives me an excuse to stay inside this afternoon and work on my Journal. I am adding the hyperlink for a web page at Purdue University Entomology/Research. I am sure there are serious iris gardeners out there who need (and would like) to learn more about this critical subject than what I am able to supply here. A borer infestation left unchecked can cause serious damage and losses in iris gardens. Borers can be a daunting challenge with raising irises, BUT it can be overcome and eradicated with a few simple steps. I will update this ongoing job as time permits. This site shows six pictures illustrating iris borer damage, symptoms and the borer itself. Here is the link: http://www.ppdl.purdue.edu/PPDL/weeklypics/Weekly_Picture7-2...
NOTE: References to any product, university or method of application are NOT a specific reccomendation or endorsement of ANY one name, brand or method! EACH individual must decide and make informed choices as to what is best for that person. This statement applies to ALL entries in this Journal as well as any/all updates.
This week I spent some time "observing" for borer damage, and sure enough I found it in two clumps! It's not difficult to find, and the following pictures will illustrate what to look for as well as the larva itself. The first picture shows a leaf fan with significant signs of damage and borer infestation. Notice the yellowing color of the second leaf and the chewed edges of the leaf beneath my thumb. This, in my experience, is always 100% proof that a borer has entered the fan, and at this stage (and time: Aug.1) has migrated to the rhizome gorging itself and destroying the plant. I am entering several entries here to illustrate various points, and this one is the FIRST thing I look for.
Aug 2, 2006
Here I have turned the fan over to show the other side. I do this for those irisarians who have not known what to look for. In my own gardens some of the more than 120 irises I grow have developed into large clumps with many fans. And damage can sometimes be overlooked or missed, especially in the center of the clump. I also want to re-state at this time (August 1-2) the larva can, and most likely is well beyond an inch in length.
Aug 2, 2006
In this picture I have peeled away the damaged leaves to illustrate why they look so sickly in the preceding pictures. This picture also shows the larva has indeed entered the rhizome by the hole between my thumb and middle finger.
Aug 2, 2006
Here I have scraped away some of the soil and turned the rhizome to a better angle to show the entry hole.
Aug 2, 2006
In the following pictures I have taken my surgical "instrument" out of my pocket (knife) to get to the root cause of the problem. Here I have sliced off the old parent rhizome part, and nearly cut the borer's "tail end" off in the process. This picture shows the bottom end of the larva protruding from the hole.
Aug 2, 2006
This is the same rhizome lying on the cement walkway behind the back patio. I also wanted to illustrate in this picture the nice increase forming on this rhizome at the top of the picture. I have since (yesterday) saved this rhizome and replanted it (along with a little borer 'medication').
Aug 2, 2006
This picture shows the larva fully "extracted" from the saved rhizome. The next entry will show it pictured on a yardstick for measuring. This rhizome was saved and replanted after treating with a fungicide and an insecticide.
Aug 2, 2006
And here is the villain of this whole problem. I really had to work to get it to stay on the yardstick for measurement (fully 1.38") and to get this picture. Had I not intervened it could have spent the rest of August eating and destroying this rhizome and others in the clump.
Aug 2, 2006
I hesitate to add this entry because of the nature of the material. However, I feel it is important in understanding the iris borer and its deadly garden habits. This picture shows accumulated fecal waste from the borer inside a leaf from the neck of the above rhizome. I had to split the leaf open to show this dreaded part of the process.
Aug 2, 2006
This serves only to show a couple other rhizomes that were saved from the borer. These are a different cultivar than the one shown above. Here I have stripped away all outer leaves and replanted.
Feb 22, 2008
Due to D-Mail requests for borer pictures I am adding a few more of them in this journal entry. These are random shots from my summer 2007 "borer hunts", and I hope they will be helpful to gardeners who have an interest in protecting their irises. This first one shows a sure sign of borer damage.
Feb 22, 2008
A close up showing the ugly critter devouring the rhizome.
Feb 22, 2008
Here I have trimmed away a lot of rhizome to expose the borer.
Feb 22, 2008
And here I have prodded him out with the point of my pocket knife.
Feb 22, 2008
This picture shows five borers on a paper towel after a day of hunting. These were all in various locations throughtout the iris beds, and eradicating them in summer means less of them to pupate and grow into adult moths later.
