When do borer moths hatch?

I seem to remember it was Sept - Oct. Does anyone know more definately? Is it a temperature thing?
The reason I am asking is that I want to try using an insect barrier netting to keep the moths from getting near the plants.
Thanks for any advice.
Another question:
This is the time to divide sib's, right? Mine did not bloom well at all this year, so maybe they are overcrowded?

Here in eastern Ontario, Canada USDA zone 4b-5, they emerge out of the soil around mid-September. I do a thorough garden cleaning in mid-October to make sure I get rid of all eggs in the debris then place the lot in the garbage, NOT the compost pile! What was missed, if any, then hatches and starts chewing their way into the new fans around the same time as the Daffodils are in bloom.

Around the last week of May, I check fans very closely for chew marks. If present, I squeeze/pinch between my forefinger and thumb along the fan from the top to the bottom until I hear it 'POP'. It can be quite a job if you have hundreds of Iris but the cleaner the beds are both spring and fall, the chance of borer damage are decreased considerably.

The photo attached is of a mature fella on July 30, 2007 when we were relocating the beds.

The borers seem to hatch before I get out in the spring to spray. My iris didn't do well this year either and those that didn't bloom had no reason not too. I was disappointed. I too am dividing and sharing with family this fall. I just have to wait for the mosquitos to disappear first.

Would it be of benefit to now spread the Bayer Grub treatment granules ?

thanks

No don't bother with the Bayer grub treatment now. It is a waste of time and money. Spread in the early spring.
Laetitia

The directions on the package that I purchased said to apply it in the Spring after two consecutive days of 72 degree weather.

This is something I've been wondering about too. My beds are lousy w/ borers and it's my 1st year w/ iris!
When you clean your beds in October of debris, does that mean just the loose stuff or do you cut everything back to the ground?
I have my iris planted with dl's and was planning on leaving the dl leaves for coverage. Should I cut them back, too?
Thanks, caitlinsgarden, for starting this thread!
LoraB.

I used to have my irises interplanted with daylilies, etc. etc., but now I moved them to their own beds so that I can keep the ground around them free of debris. I think the moths prefer to lay their eggs in the dead leaves right on or near the iris plant, so that the tiny larvae don't have far to go to get to the leaves in the spring.
I may just use the bayer product this coming spring, although I am trying to find a way around it. I am worried that my siberian iris, and other related iris may have borers around them also, but I haven't deborered them this year, only the beardeds. And now my time is very limited, as I have baby calves to take care of and only a certain amount of energy each day. Wahhhh!

LoraB:
You don't HAVE to do a good Fall cleaning to remove the borer eggs...provided you do a good Spring cleaning before they hatch! I never clean anything in the Fall, allowing old iris foliage and tree leaves to cover my iris beds. I like the idea of natural mulch covering my plants. After all, a wild iris is not cut back in the Fall, right? Of course in the Spring its scramble time...and if something comes up and I can't remove the dead leaves, etc and get the Merit down by mid April, it is borer heaven here! If you can't get the Merit down by end of April (and this will vary based on zones) don't even bother! I was late this year, and compensated by pouring the Merit on in May....but it was totally useless at that point.
Laetitia

being in Fl ... I have not heard of them... or seen any... do you think they would be here?

Sugarbean, you are so right about getting out early! For me, I think it's closer to March than April. I broke down and trimmed back all my iris this fall and tried to clean and burn all the debris. I didn't have many blooms this spring and I should have. I'll just have to try harder! They do not bother my siberian iris or the tiny border iris..

What a dreadful picture of a borer--only too true. They shouldn't be a problem in FL unless shipped with new plants. Here the eggs hatch in the spring after adult moths emerge from pupae.

I leave my leaves until march just as a little protection especially for first year seedlings. March If snow is still on the ground I put on my Bayer season long grub control and super-phosphate and as the snow melts it takes it into the ground very well. As soon as I can before any warm up I clean leaves. mid April I put down Spectracide Triazicide. I have had minimal problems except in mixed beds that I did not treat but will in the future.
:)
A

Mid - April? That's this week? EEEK! Can Merit be put on too early? The weather has only been nice enough a day or so this year to get out and clean up the garden. We had a very late and long winter this year in Iowa, zone 4B.

I am in Central Illinois and spread grub control last weekend.

drat! I'm in zone 7A to B - is it too late for Merit or grub control - i've never had them before but had one newly planted iris go soft on me immediately last year, and I think it might have had one in it. (no sign of rot, but I squished the whole foot and it had something in it)