Question: This is a photo of our daylily. The flowers are beautiful, but the leaves are striped with brown. Do you know what’s wrong with it and what we can do to keep it from happening in the future?

Answer: Daylilies (Hemerocallis species) are popular perennials for sunny areas of the landscape. Their flowers come in a broad range of colors, and the plants are fast growing and require very little care.

However, there are several common issues daylily growers face that can affect the health and appearance of the plants.

First, the most devastating daylily problem is probably daylily rust. This fungal disease didn’t arrive on North American shores until the early 2000s, but it has since spread to many different states, most likely via plants shipped from one region to another.

Caused by a fungal pathogen known as Puccinia hemerocallidis, daylily rust affects many different daylily cultivars. It’s not as problematic in northern states as it is in the south, since it doesn’t survive cold winters, but I’ve heard from some folks who have plants with symptoms.

The leaves are streaked with yellow and brown and you’ll see raised pustules on the leaf surface, particularly on the underside. When you rub the pustules, your fingertips will be orange from the spores. This pathogen will not kill plants, but it does make them look unattractive. Biofungicides based on Bacillus subtilis help prevent this pathogen, but it’s better to seek out resistant varieties.

I do not, however, believe that this is what’s going on with your plant.

Leaf streak

Another similar pathogen is daylily leaf streak. This disease is caused by a different fungus, and causes yellow, elongated splotches on the leaves, typically around the central vein. The pathogen occurs first at the leaf tip and then progresses down the leaf. There will be small brown flecks, but unlike daylily rust, there are no pustules or rust-colored spores.

It develops quickly in warm, wet weather. The spores are spread by humans and animals, and when they are splashed up onto the plant from the soil. Again, this pathogen will not kill your plant, but to prevent it, make sure plants are well spaced and use a biofungicide as a preventative.

Though this may be what’s causing the brown leaves on your plant, I suspect it’s more likely to be the following issue.

Leaf scorch

Leaf scorch is a very common physiological disorder of daylilies. It is not caused by a fungus or bacteria or virus. Instead, it’s caused by growing conditions.

Leaf scorch is evidenced by brown leaf tips and splotches on the leaves, and is especially evident in hot, dry weather. Though we had a wet spring, the last few weeks have been very hot and dry, which can cause leaf scorch to occur fairly quickly. It is largely an aesthetic issue and will not harm the plant.

I suggest “combing” through the plant with your fingers and pulling out any damaged leaves. Do this several times throughout the summer and the plants will continue to generate new leaves from the base, keeping the plant lush and healthy looking.

In fact, in my own garden, I groom my daylily plants as soon as their first flush of blooms fade. I do this by completely cutting the plant back down to the ground, including all the leaves and the dead flowering stems.

This causes a flush of new growth that is pristine and, with some daylily varieties, it will stimulate another flush of blooms.

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