My iris have been beautiful this year. They have been loaded with blooms and looking very healthy (see photo 1 taken 5/19/2021). Unfortunately, they are now showing significant signs of leaf spot disease (see photo 2 & 3 taken 5/22/2021). I lost several iris varieties a few years back due to disease. Please share your best solution to this problem. Any help is greatly appreciated.

Tina ~ Welcome to the Iris Forum!

I wish I could help you. Maybe someone here will be able to assist you.

@KentPfeiffer
@Paul2032
@crowrita1
@Australis

You probably only live 40 or 50 miles from me so I'm assuming you've had the same periods of rain, constant cloudiness, and high humidity that we've had over the past week. Those are perfect conditions for leaf spot. My irises looked spectacular last week, but many are afflicted with leaf spot now.

Fortunately, leaf spot doesn't generally do any harm. Unfortunately, there also isn't much that can be done to prevent or treat it. You can pull off the leaves that are most affected if you wish, it will make the irises look better and it certainly won't hurt them.

The thing we need to worry about is, if our weather continues to be wet AND it get hot, then soft rot of the rhizomes becomes possible. Soft rot requires intervention. Anytime you detect it, you'll want to clear as much vegetation/detritus from around the affected rhizomes as possible, then scoop the rotten stuff out and dispose of it. Some people will then treat the wound with Comet or a 10% bleach solution, but I think sunshine is the most effective treatment.

Tina, your fence row of irises is beautiful!

DaisyDo said:Tina, your fence row of irises is beautiful!

I agree, it's really beautiful.

Iris borers can also be a problem. A good clean up of dying foliage and debris in late fall helps and systemic insecticide in spring can provide additional control.

Any "treatments" for leaf spot needs to be done, before you ever have leaf spot ! For general iris health, you need "uncrowded" plants...so they get air and sun, a "clean slate", in the previous year...all the trash, dead leaves, stalks, etc., removed , and "trashed' (not composted). The "fungal spores" that actually cause the fungal type of leaf spot are 'everywhere', so, if the amount in the beds can be reduced...you will have less leaf spot...solarization works, as do fungicides (if you aren't against using "chemicals"')...fungicides need to be applied, starting when "new growth" begins, and continued throughout the growing season...a spray every 10days-2 weeks, depending on rainfall amounts...it also helps to "switch off" fungicides, as the spores will become "immune", if the same chemical is always used.
That said...you are still going to have leaf spot ! Hopefully, not much, and not everywhere in the bed, but, when the humidity sets in
As to trimming the leaves, for better appearance , yeah, it makes them look better....if there isn't a BIG problem...if there is, well, irises don't "look right" with only one, or two, stubby leaves ! And, when you are "in the beds", trimming spotted leaves, you are dropping spores from those "trimmings", or brushing against the "spots" on one plant, and depositing them on another. Your pets can be "culprits" in this, as well. And, IMHO, even a "badly spotted" leaf....say only 50% green, supplies 50% more "ooomph" to the plant than NO leaf does, so I don't remove any leaves, until they are "spent".
Some cultivars are more prone to leaf spot, than others, and SIB's, and Spuria irises seem pretty well immune to it, so , that could be an option, too.
One thing, the "treatment" for fungal leaf spot prevention (clean beds, air flow, sun exposure, etc.)also are big helps for the prevention of the bacterial form of leaf spot, and both fungal, and bacterial rot.

Good comments Arlyn. I'd like to do an evaluation of leaf spot some time with my irises. I haven't worried too much about it yet since I mostly have just rows of iris, rather than landscaping. Once I begin incorporating more iris into landscapes, I may try to select those with less leaf spot. If I really want a particular iris, but it suffers from heavy leaf spot, I may try to situate it so that other plants screen the foliage from sight--without shading the iris.

One thing that I used to see done, was , after bloom was finished, they would cut the foliage down, at the same time they cut the spent stalk. That DID make for much "cleaner" leaves, in the late summer...but, it sure "robbed" the plant of growth. As I sad, I'd rather have 'ratty' leaves, than "no" leaves, but, I guess it depends on how important "clean" foliage is to the person

Thank you all for providing this useful and reassuring information. I will hope that Mother Nature provides some less humid days and I will continue to monitor the rhizomes for signs of soft rot.

Here's hoping!

to the iris forum Tina