Easter lilies (Lilium spp.) are one of the most popular potted flower crops grown in the Northeast. They are also one of the most challenging to grow because the timing of Easter changes yearly, and the long duration of the crop necessitates constant care and attention. Most of the commercially important lilies are L. longiflorum cultivars, as well as Asiatic and Oriental hybrids. There are a number of diseases, nematodes and abiotic disorders affecting potted Easter lilies.
Botrytis blight
Botrytis blight (Botrytis cinerea and B. elliptica) is one of the most significant diseases of lily. Spores that blow onto plants from neighboring infected crops or debris are important in initiating the disease. B. elliptica is considered the more significant species affecting lilies over B. cinerea.
Initially, small water-soaked spots appear on the leaves that continue to expand when conditions are favorable for infection. All parts of the plant are susceptible. Masses of gray spores are produced in the lesions during periods of high humidity and spread to nearby leaves. The flowers are especially susceptible to Botrytis and rapidly turn brown and die. Even a small percentage of brown flowers is not acceptable for this crop. The spores of the pathogen will germinate and infect within 6 hours of leaf wetness at 68 °F. Botrytis is able to survive as sclerotia in soil, media and in crop debris.
Management takes an integrated approach, including sanitation, cultivar selection and fungicide application. Plant into clean pots, disinfest benches and equipment, ensure incoming bulbs are free of disease and remove debris at the end of a cropping cycle to limit sources of inoculum. Cultural controls, including good air movement within the crop canopy and limiting overhead irrigation, can limit conditions favorable for the pathogen. Crop resistance is available in the Oriental lilies. The cultivars ‘Conca d’Or’, ‘Time Out’, ‘Sorbonne’, ‘Casa Blanca’, ‘Le Rêve’, ‘Tiara’, ‘African Queen’, ‘Cobra’ and ‘Mozart Zanlazart’ have been shown to have partial resistance based on field trialing in New York.
Fungicide application is essential to manage this disease in the greenhouse. There are several effective fungicides available, including Decree, Mural, Empress, Astun, Postiva, Pageant Intrinsic, Daconil and Broadform. Biological products based on Bacillus spp. and Trichoderma have been tested and may also provide control.
Symptoms of CMV
Fusarium basal rot
Fusarium oxysporum is a commonly isolated pathogen causing basal rot. Cylindrocarpon sp. may also be a cause. These pathogens likely come from the Pacific Northwest, where the bulbs are produced. Fusarium degrades the scales and cortical tissues with destruction of the basal plate. The rot can also move from the basal plate to the scales, causing brown lesions that develop along the scale. Roots either do not develop or develop weakly. Above-ground symptoms include yellowing and stunting. The pathogen is especially problematic during winter, when growth is slower and the potting media stays moist for long periods. Management includes fungicide dips of bulbs and sanitation. Apply fungicides as a dip immediately upon arrival of the bulbs. Top-performing fungicides include Empress Intrinsic, 3336, Postiva and Mural.
Cucumber mosaic virus (CMV)
CMV appears on lily leaves as a light-green mosaic, with gray necrotic spots in the longiflorum species and brownish necrotic spots in Asiatic cultivars. Cell death causes the flecking appearance in the leaves. Plants may be stunted, with brittle leaves and deformed flowers after infection. Affected plants usually have small flowers that are not saleable. CMV is transmitted by several aphid species and by mechanical transmission through contaminated knives, machines or water. Start with virus-free planting material, monitor and control aphids and remove virus sources by rogueing crops showing symptoms. Test plants through a clinic to check for CMV.
Lower leaf yellowing
Leaf yellowing in Easter lilies can occur as a gradual or sudden process. Gradual leaf yellowing typically begins as plants reach the visible bud stage of development.
With gradual yellowing, leaves at the base of the stem begin to yellow and die one by one. As the disorder progresses, the lower stem becomes bare and plants appear leggy. Sudden or catastrophic yellowing typically occurs in the post-harvest environment after the flowers begin to open. This disorder is characterized by large numbers of leaves simultaneously yellowing and dropping from the stem.
Several factors have been linked to leaf yellowing. Lilies treated with growth regulators to control height are more prone to leaf yellowing disorders than untreated plants. The growth regulators used on Easter lilies inhibit the natural production of the hormone gibberellic acid. A second key factor is root stress and root rot. Gradual leaf yellowing often follows the occurrence of root rot, and plants with poor roots are more susceptible to sudden post-harvest yellowing.
Another factor involved in sudden post-harvest yellowing is time in cold storage. Lilies subjected to cold storage are more prone to sudden leaf yellowing, and as the time in storage increases, so does the susceptibility to this disorder. Growth regulators containing GA4+7 (e.g., Fascination) can reduce leaf yellowing. Apply late in the crop cycle to minimize stem stretch. GA4+7 applications do not reverse leaf yellowing. Apply this spray as soon as the first leaves begin to yellow. This growth regulator must be applied carefully; consult the label for application timing and methods.
Author’s note: Please read the pesticide label prior to use. All agrichemical/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. No endorsement of products is intended, nor is discrimination intended for products not listed. Registration of pesticides varies by state; consult and follow labels for registered use. To avoid any potential phytotoxicity or residue problems, spot test before widespread use.
Charles Krasnow is a University of Connecticut extension specialist. Contact him at charles.krasnow@uconn.edu.
