Greetings from the garden bed. We daylilies (Hemerocallis) are generally resilient plants, but like all living things, we face our share of challenges. Pests and diseases can diminish our vigor, disfigure our foliage, and ruin our beautiful blooms. Understanding these threats from our perspective is key to maintaining our health. Here is a detailed account of the most common adversaries we face in the United States and how you can help us recover.
From our point of view, the most troublesome pests are those that suck our vital juices or chew our tissues to shreds.
Aphids: These tiny, soft-bodied insects cluster on our tender new shoots and flower buds, piercing our skin to feed on sap. This feeding weakens us, causing leaves to curl and distort. Worse, they excrete a sticky substance called honeydew, which attracts sooty mold and can interfere with photosynthesis. A strong spray of water from a hose can often dislodge them. For heavier infestations, insecticidal soap or neem oil applications are effective and gentle on our system.
Spider Mites: These are nearly microscopic pests that thrive in hot, dry conditions. They live on the undersides of our leaves, sucking out chlorophyll. The first sign we show is a subtle stippling or yellow speckling on the leaves, which may eventually turn bronze and dry up. You might also see fine webbing. Increasing humidity and regularly spraying the foliage with water can deter them. Miticides or horticultural oils are necessary for severe cases.
Thrips: These slender insects are particularly maddening as they rasp and suck on our developing flower buds. This damage results in buds that fail to open, or flowers that are streaked, discolored, or deformed when they do bloom. Because they hide inside the buds, they are difficult to control. Systemic insecticides can be helpful, but applying them early, before the flower scapes emerge, is crucial.
Diseases often stem from environmental stress or fungal pathogens that attack our roots and leaves.
Daylily Rust (Puccinia hemerocallidis): This is a significant fungal disease. It appears as small, raised, yellowish-orange pustules on the undersides of our leaves. The upper leaf surface will show corresponding yellow spots. This rust weakens us by disrupting our ability to photosynthesize. It is crucial to remove and destroy all infected foliage. Ensure we have good air circulation and avoid overhead watering to keep our leaves dry. Fungicides containing chlorothalonil or myclobutanil can be used preventatively.
Leaf Streak: This fungal disease causes yellow streaks along the midvein of our leaves, which eventually turn brown and die back from the tips. It is most prevalent in warm, wet weather. While it is rarely fatal, it makes us look unsightly. The best treatment is sanitation—remove and dispose of infected leaves in the fall. Fungicides can be applied in spring if the problem was severe the previous year.
Root Rot (Crown Rot): This is often the most devastating problem we can face. Usually caused by fungi like Sclerotium or bacteria in waterlogged soil, it causes our roots and the crown (the base of the plant) to become soft, mushy, and foul-smelling. The foliage will yellow, wilt, and collapse. Prevention is the only real cure. Please plant us in well-draining soil and avoid planting too deeply. If rot is detected, you must dig us up, cut away all the rotted tissue with a sterile knife, and replant us in a fresh, well-draining location.
