Asiatic lilies are popular, cold-hardy hybrids known for being among the first lilies to flower in the season. While generally robust, they can encounter common garden issues that disrupt their growth and flowering display. Addressing these challenges requires identifying whether the problem stems from an insect, a pathogen, or environmental stress. Understanding the specific symptoms and applying targeted solutions will ensure these perennials remain healthy and productive.
Identifying and Eliminating Key Pests
The most destructive insect threat is the Red Lily Beetle (Lilioceris lilii), easily identified by its bright, scarlet-red wing cases. Adults emerge in spring to feed and lay orange-red eggs on the underside of foliage. They cause damage by chewing holes in the leaves, weakening the plant.
The highly destructive larvae hatch from these eggs. Larvae are reddish-brown but covered in black, slimy excrement (frass) for camouflage. They cause greater damage than adults, often defoliating entire stems.
The most effective initial control is diligent handpicking. Since beetles drop to the ground when disturbed, adults and larvae should be dropped into soapy water. Routinely inspect leaf undersides for eggs, scraping them off or removing the leaf entirely.
For heavy infestations, organic insecticides target the soft-bodied larvae. Neem oil acts as a repellent and growth inhibitor when applied to young larvae. Spinosad, derived from soil bacteria, is also effective when applied weekly during the active period.
Asiatic lilies also host common garden pests like aphids and spider mites. Aphids cluster on new growth, sucking sap and causing leaves to curl and yellow. Spider mites, prevalent in hot, dry weather, cause fine yellow stippling on leaves, sometimes with fine webbing. Both pests are managed by applying insecticidal soap or horticultural oil, ensuring thorough coverage, especially on leaf undersides.
Controlling Common Diseases
Asiatic lilies are susceptible to Botrytis Blight (lily fire), a fungal disease favored by cool, damp conditions. Symptoms begin as small, water-soaked spots that are reddish-brown to tan, often with a purple margin. These lesions quickly enlarge, potentially killing the foliage and forming a fuzzy, gray mold during wet periods.
Prevention is the best defense, as the pathogen overwinters in plant debris. Ensure good air circulation by avoiding overcrowding and spacing plants adequately. Water at the base of the plant in the morning to allow moisture on the leaves to dry quickly.
If infection occurs, promptly remove and destroy all infected material and fallen debris to reduce the fungal load. Chemical control involves applying a targeted fungicide, such as a copper-based product, at the first sign of infection. Alternating fungicides helps prevent the development of resistance.
Basal rot, caused by the fungus Fusarium oxysporum, targets the bulb’s basal plate due to excessively wet soil or poor drainage. Above-ground symptoms include yellowing and stunting of the foliage. Infected bulbs show a chocolate or bluish-gray rot extending from the basal plate into the scales. Infected bulbs must be destroyed and never composted to prevent the fungus from remaining in the soil.
Asiatic lilies can also contract viral diseases, such as the Lily Mosaic Virus, typically spread by sap-feeding insects like aphids. Viral symptoms include leaf mottling, streaking with light green or yellow patterns, and distorted growth. Since there is no cure, immediately remove and destroy the entire infected plant to prevent the virus from spreading.
Resolving Cultural and Environmental Issues
Lack of Blooms
A common disappointment is a lily plant that produces healthy foliage but fails to bloom. The primary cause is insufficient sunlight, as lilies require a minimum of six hours of direct sun daily for flowering. Overcrowding is another factor; dividing dense clumps every few years ensures bulbs have adequate space and nutrients.
Improper fertilization also inhibits flowering, especially if the plant receives excess nitrogen. Nitrogen encourages lush foliage growth at the expense of flower buds. Use a balanced fertilizer and avoid high-nitrogen formulas. Bulbs should also be planted at the correct depth, typically three to four times the height of the bulb, for stability and insulation.
Addressing Leaf Yellowing and Scorch
Leaf yellowing often signals cultural problems rather than disease. Yellowing of the lower leaves signals overwatering or poor drainage, which stresses the roots and can lead to basal rot. If the soil is heavy or saturated, improving drainage or replanting in a well-drained medium is necessary.
Yellowing combined with brown, dry edges (scorch) suggests the plant is not receiving enough water or the roots are overheating in hot weather. While the plant prefers full sun, the roots benefit from a cool environment. Apply a layer of organic mulch around the stems to achieve this.
Asiatic lilies thrive in a slightly acidic to neutral soil pH (6.0 to 6.5). Nutrient uptake, such as iron, can be hindered in overly alkaline soils.
Winter Preparation
Proper winter preparation is necessary for the long-term health of the perennial bulb. Although cold-hardy, applying a protective layer of organic mulch (straw or shredded leaves) after the foliage dies back helps insulate the bulbs during the coldest months. Wait until the foliage has naturally turned brown in the fall before cutting it back, as the leaves store energy in the bulb for the following year’s blooms.