Leaf streak is a common disease of daylilies, affecting daylilies wherever they are grown. Daylily varieties can vary widely in terms of their susceptibility to the disease. Often leaf streak is a cosmetic problem, causing slight damage. In some cases, however, leaf streak can cause substantial leaf loss, and sometimes may lead to complete defoliation of daylily plants.

Leaf streak symptoms often initially appear as yellowing that begins at leaf tips and spreads down along and outward from the midveins of leaves. This tissue eventually browns and dies. As the disease progresses, complete leaf death can occur.

Leaf streak is caused by the fungus Aureobasidium microstictum. This fungus overwinters in infested daylily leaf debris where it produces spores that initiate the disease each spring. Spores produced on infected leaves lead to additional infections. The disease is most common in warm, wet weather. This pathogen is spread from leaf to leaf and plant to plant, primarily by water splash.

To minimize the spread, sanitation is an important management technique. It is best to remove infected leaves as they appear and fertilize and water your plants properly to promote growth of new leaves. DO NOT water with a sprinkler, as it can spread the fungus. Instead, use a watering can, a watering wand aimed at the base of the plant, or a drip hose to apply water directly into the soil. To further limit pathogen spread, avoid working with plants when they are wet.

Infected daylilies should be isolated from healthy plants. Daylily leaf streaks may be avoided by purchasing disease-free stock plants and propagating only from healthy specimens. In the fall, remove dead foliage from around the base of the plants and dispose of the clippings (in trash or hot compost), as the fungus will overwinter on old foliage, and spores will be produced the following spring to infect new leaves.

There are several fungicides that have been shown to be effective against leaf streaks on daylilies. These include copper-based fungicides, chlorothalonil, and mancozeb. Copper-based fungicides, such as Bordeaux mixture, have long been used to control fungal diseases in gardens. They work by disrupting the cellular processes of the fungi, preventing their growth, and spread. Chlorothalonil is a broad-spectrum fungicide that can effectively control leaf streak and many other fungal diseases. Mancozeb is another broad-spectrum fungicide that is effective against leaf streak and can be used as a preventive measure.

Before applying any fungicide, it is important to carefully read and follow the instructions on the label. This will ensure that the fungicide is applied at the correct rate and in the correct manner. It will also provide information on any safety precautions that need to be taken, such as wearing protective clothing or avoiding contact with the treated plants.

Examples of resistant daylily cultivars include Betty Bennet, Edna Spalding, Ella Pettigrew, Globe Trotter, Nancy Hicks, Pink Superior, Ron Rousseau, Sudie, Tropical Tones, Upper Room, and Winsome Lady.

Here a few Extension articles you may find useful.

Daylily Streak and Daylily Rust, June 2, 2012.pdf (unl.edu)

Daylily leaf streak – Collecephalus hemerocalli - Plant & Pest Diagnostics (msu.edu)

Daylily Leaf Streak – Wisconsin Horticulture

Thank you for your question and have a great gardening experience.

1. I wanted to know what Daylilies that are available to be purchased in 2024 or so that are resistant to leaf streak.
2. The other question was why the older Daylilies are resistant to Leaf Streak and perhaps not the newer ones.
   

On 08/02/2024 6:33 PM EDT Ask Extension <<personal data hidden>> wrote:

 

 

The ability of daylilies to resist leaf streak can indeed be related to their rhizomes, as older varieties that were developed in the 1960s and have rhizomes are more likely to be resistant to leaf streak. However, the resistance to leaf streak isn't solely dependent on rhizomes. It's also influenced by the genetic makeup of the plant and its ability to resist the fungal pathogen Aureobasidium microstictum that causes leaf streak.



As for newer daylilies that resist leaf streak, while the article from Wisconsin lists some older varieties, it does not provide a comprehensive list of newer ones. It's important to note that resistance to leaf streak can vary, and even resistant varieties may not perform well every year and under all environmental conditions.



To find newer daylilies that resist leaf streak, you might want to check with local nurseries for the most current information on resistant varieties. They may have access to more recent breeding efforts and can provide you with a list of daylilies that have been bred for resistance to leaf streak. Additionally, you can look for varieties that are known to have good disease resistance, as this often includes resistance to leaf streak.



Remember, while it's important to choose resistant varieties, it's also crucial to follow good cultural practices, such as proper watering, avoiding overhead irrigation, and removing dead leaves in the fall, to help prevent leaf streak and other diseases