Watch Out! Crown Rot is Here

About this time last summer, I briefly mentioned a plant disease the gardeners and I were dealing with in the Minnetrista Boulevard planting bed. Called crown rot or southern blight, it was making quick work of hostas.

One year later, I wanted to write about it again, because guess what? We still have it and it is killing more hostas.

Crown rot is caused by several soil-borne fungi and it affects hostas, sedum, iris, hydrangea, and many other plants.

Hosta showing extensive crown rot infection.

The first symptom is usually a yellowing of the leaf, and then the leaf collapses and dies. The yellowing is caused by girdling that the fungus does to the stem, preventing food and water from reaching the leaf tissue. It will appear water soaked and have a lesion on the base of the stem. You will often notice little sphere-shaped structures called Sclerotia. Those are what allow the fungus to overwinter.

Close-up of stem lesions and Sclerotia.

Professionals in the plant industry first hoped that this was only a southern disease because they assumed it couldn’t overwinter in the colder north. Unfortunately they were wrong.

Last year, we went with the common advice. We removed and destroyed all the infected plant material. We left blocks of hostas that seemed unaffected and began to research about the next steps of preventing the crown rot from spreading.

Hosta showing early crown rot symptoms with yellowing leaves.

There are fungicides that can be sprayed to prevent this disease, but while doing my research I found all of them to be problematic around waterways. Having the White River right next to the planting bed made it a quick decision to not spray.

That left us with the options of waiting and seeing if our removal of infected plants last year helped. It certainly looks like it didn’t.

Next steps will be to remove the rest of the infected hostas and make sure we disinfect the tools we use to do so. We will then plant more plants but ones that aren’t susceptible to the blight.

Now, if you have hostas or other susceptible plant material, start monitoring and act fast if you see it!