It works because it is a systemic insecticide. Anything that eats the plant dies. Also, if you have anything you eat close to where you grow iris, then a systemic will be in those plants as well, meaning you will be eating it. Using systemics on a plant that flowers is just cruel, since bees are drawn to flowers - it risks killing bees and whole hives. I've been using the correct nematodes (from Arbico Organics) to battle borers, and it seems to have stopped them in their tracks. After a few years where I was concerned about losing lots of iris, I'm seeing blooms this spring in colors I haven't seen in years.

drmbear Cherry... Thanks for the info on the nematodes. I work at a greenhouse where we use beneficial insects to control aphids, thrips, whiteflies, etc... I myself have been much more diligent in getting away from chemicals in the garden. I was not aware there was an organic approach to controlling Iris borer. I will need to check out Arbico Organics

Years ago Paul Black from mid-america gardens posted an article in the American Iris Society magazine talking about how they dealt with borers on their HUGE commercial iris farm. Borers do not over-winter in the rhizome, but instead the eggs are attached to the previous years leaves. The approach recommended was to wait until the ground was frozen but also dry and then use a roofing torch/asphalt torch connected to a standard grill propane tank to rapidly scorch the dead material without damaging the rhizome. When I had a bigger yard I had very many iris, and this method was nearly 100% effective. I usually do the work January or early February.

Cheers,

Werner

I usually just cut all my foliage down to the rhizome in November when the plants are dormant and that gets rid of the eggs that are on the leaves. I also don't compost the leave but remove them from the property.

Worked for me - wonderful bloom compared to last year.