Is it too late to treat? Dry and hot in southwest Kansas. Iris are overgrown and need to be separated. Seems to be spreading. Should I dig them all out? If I cut the leaves down, can I spray for the fungus then or not?
My Nursery Said in the Spring My Iris Had a Fungus
Certified GKH Gardening Expert
Heterosporium leaf spot, or iris leaf spot, is the most common disease of iris plants. Leaf spotting is most conspicuous on the upper half of the leaves toward the end of the season after the blooming period...eventually working its way downward. This fungus overwinters on dead iris leaves and the spores spread from old plants and rain splashing. Removing and discarding all diseased leaves in the fall (or now) will greatly reduce the infection and should provide sufficient disease control. For more severe cases, fungicides are also available but these are normally applied in spring. For additional information, this article should help: https://www.gardeningknowhow.com/ornamental/bulbs/iris/iris-leaf-spot.htm
Also, if overcrowding is becoming an issue, go ahead an dig them up and divide. Here is more info: https://www.gardeningknowhow.com/ornamental/bulbs/iris/dividing-transplanting-iris.htm