are my daylilies destined to die?

Asked July 26, 2018, 9:38 AM EDT

I have a large daylily bed (30'X60'). I leave garden cleanup 'til early spring, when I burn last year's foliage. Apparently I have acquired "leaf streak" in parts of my bed & it's killing some of my favorites. Are all of my daylilies destined to die? What can I do to get rid of or reduce the damage? The bed is the result of many years of acquiring daylilies for near continual blooms & moving them around for optimal impact. I'd hate to lose them & have to start over or (gasp) not have any at all. Can my bed be saved? Thanks. Deb Ackley

Benton County Minnesota

8 Responses

Thank you for the question. Treatment of any plant problem depends on accurate diagnosis. Here is a link to photos and a description of the disease from Purdue Extension:
Assuming you have diagnosed your problem correctly, rest assured that you can help your plants. The key point is that leaf streak of daylily doesn't kill the roots of the plants but will kill or damage the leaves. The fungus does overwinter on plant debris so your practice of waiting until spring to clean up may be contributing to the problem. For now, you can remove infected and dead leaves, clean up around the base of the plants, and avoid overhead watering. When planting or transplanting plants, make sure there is space around each plant to allow for airflow that will aid in keeping the foliage dry. This fall, cut plants back and clean up all debris to reduce the fungal load that overwinters.
On a personal note, I have battled this disease in my daylily bed for 3 years and have found that dividing plant clumps and regularly removing damaged or dead foliage
allows my flowers to bloom beautifully while keeping the fungus at a minimum. I have not needed fungicides.

Good luck and thank you for contacting Extension.

Thank you so much.

Is it OK to use wood mulch in the daylily bed or will it harbor the fungus?

Good question. Advantages of wood mulch are that it helps control weeds by reducing germination of weed seeds, maintains soil moisture by reducing evaporation, and keeps the soil temperature constant, insulating against temperature fluctuations. Since it is organic, it breaks down over time with help from normal soil organisms like bacteria and fungus, and with insect help. Most of these are beneficial so there isn't a definite answer to your question. I think that once you get your daylily bed cleared of the majority of infected leaves now, and cut it all back this fall, the streak fungal load will be greatly reduced. Furthermore, I think it would be wise to leave the soil open to air the rest of this season to let air flow and sun help control the problem
It might be OK to add a mulch layer of no more than 2 inches around your plants next year.

The lily bed is quite large (see pics) & removing only the dead/infected foliage is a daunting task. It would be easier if I cut back foliage of all to 3-4", clear out the mulch/dead plant matter, fertilize & treat with a fungicide. Would that be OK to do now? I'd rather lose the rest of this year's blooms than any more of my specimens. I'll thin (another daunting task) from now 'til spring. Would I be better off using MiracleGro (high nitrogen), "Bloom booster" (high phosphate) or a balanced (10-10-10) fertilizer at this time? I appreciate all your helpful advice.

Thank you for the nice photos. Actually, your plants don't look bad. I can appreciate all the work required to methodically pick off the affected leaves and your desire to make the process more efficient, but cutting all the plants off to 3-4 inches would be the wrong thing to do right now. The many green leaves are photosynthesizing and storing energy in the roots for the winter. If you cut them all off now, you will greatly reduce the plans ability to do this and they may not make it through to spring.

If you want to lightly fertilize, do it soon so that new growth isn't stimulated too late in the summer or fall. Any general, any balanced fertilizer is fine and one isn't recommended over another.

... and I suppose my deadheading ritual of "snap & drop" doesn't help, does it? As you may notice from my pics, I have a "border" of Stellas & Happy Returns. Is there a recommended clump size & distance between clumps? I love the look of drifts of color. Thanks for your advice. It looks like there'll be a BIG daylily sale next spring. :)

You are correct! Dropping plant debris on the soil around the plants with known disease may contribute to spread or continuation of the problem. Clump size is usually determined by vigor of the plant. Over time, the clumps can hollow out, leaving a doughnut shaped clump. It's definitely time to divide and conquer at that point. Otherwise, clump size isn't really a problem unless they all run together, limiting air flow. I can't tell you exactly how far to space plants. The front row of Stella de Oro (which is the only area I can see clearly) look a bit crowded. I think if you removed part of a clump every 1-2 feet or so, the air flow would be greatly improved and you may have even better blooms. You will know you have succeeded when disease levels drop. As you have probably figured, some of this is trial and error. Expect to see some disease next year but keep up with your sanitation efforts and only the beautiful blooms will be noticed.