DISEASES that can affect Daylilies


A variety of fungi can attack daylilies. Most are not fatal or extensive and can, therefore, be ignored. However, a few are serious and some have no cure. Therefore, if a fungus appears, I treat it.

One fungus is what we call 'leaf streak.' Normally, it causes no real damage to either the plant or the bloom. It simply looks ugly because it causes yellow to pale-yellow streaks on some of the leaves. Usually I just ignore it; however once in a while it can get bothersome and I will spray with a fungicide and trim the leaves (especially when I know I might have garden visitors).

Note that daylilies can also be infected by bacteria. Erwinia is an example. Unlike fungi, daylilies can die of a bacterial infection. The result is plant death and rot. You may hear someone say they lost a plant to rot. What they really mean is that their plant died and rotted, probably from the result of a bacterial infection. This is not common, but I believe is an opportunistic infection. By this I mean that the bacteria is probably in everyone's environment, but takes hold in a daylily only if the conditions are "right." Conditions such as weak plants, high humidity and high temperatures are some. This is why, in my opinion, "rot" occurs more in the South; it's simply hotter there longer. For these reasons, plant only in the Spring or early Fall, and avoid planting in summer.

Some growers report an occasional plant that turns 'sickly' in spring. Hence, the malady is called 'spring sickness'. The plant, or perhaps only some of the fans of one clump, may turn pale and look like wilted lettuce. The affected fans also twist and can become very contorted. Some people suspect a fungus; others a small insect that feeds on the new growth. I have experienced this a couple of times. Sometimes I treat with a fungicide; sometimes a pesticide; sometimes both; sometimes neither. In no case did I lose a plant to this mystery-just some of its early growth.

If a newly planted daylily starts to turn yellow within a couple of weeks of planting, it may be infected with a fungus or bacteria. ALIETTE, PHYTON 27, 50% wettable CAPTAN (two tablespoons to a gallon of water), or some other fungicide poured on the fans usually will save them. Some gardeners treat all purchased plants this way when planting them, as a preventative measure. But fungicides, as well as many other gardening chemicals, can be very hazardous and therefore should be handled with care. Also, not all fungicides are safe to use on daylilies. Some of those I use may be difficult to find, at least in small, affordable quantities.

I will not use Benlate/Benomyl. Years ago the maker, DuPont, was sued because many users of Benlate accused the product for stunting nursery plants. I do not know the outcome of the suit, and the wettable powder form of Benlate is supposed to be effective and safe, but I am satisfied with the others I use.

There's really a lot more to say about fungi, but my expertise is limited. Join the AHS and read past issues of The Journal for more.

Starting with the Millennium, a new fungus started spreading across the US. Daylily RUST is now present in almost all states. It seems to affect daylilies worse than the more common 'Leaf Streak' fungus, and the ultimate outcome is yet unknown. Because it is new, it is highly feared by many daylily growers. Although it makes some affected cultivars look VERY ugly, it is apparently NOT fatal and responds to many fungicides, such as protective sprays like Daconil and a Mancozeb with Heritage. Others include STRIKE 50 WDG (Triadimefon) and systemics like Bannermax, Heritage, and Contrast. Latest (Jan 2015) from the MO Dept of Agriculture: Compass O, MilStop, Spectator, Compass, or Eagle 40 WP. An instant contact spray mainly used as a dip (used by some sellers before shipment and buyers upon receipt) is Zerotol.

Two good choices for gardeners with small collections, because they can be found more easily and in smaller quantities are Immunox (myclobutanil) from Spectracide and Funginex (triforine) from Ortho.

There is a new, mysterious affliction that has recently showed up in not only my garden but others in the area, and perhaps even nationwide. At this point, we do not know if it is a fungus or a bacteria. It can be very damaging by destroying entire bloom scapes and even the entire plant. It manifests itself first by causing a bloom scape to wither and die, right before any blooms open. It can then spread outward from the scape into the surrounding leaves. Cause and cure are currently unknown. Some think it is simply a bad form of leaf streak fungus.


Leaf Streak

picture of leaf streak fungus on daylily


'Spring Sickness'
picture of disease we call spring sickness


Daylily Rust
picture of daylily rust


Mysterious new 'scape withering' disease
damage from mysterious new scape withering