Greenhouse IPM: Lily Basal Rot and Bulb Mites in Easter Lilies

Easter lilies are not an easy crop and a grower must be very regimented in their production approach so that they will be heavily budded or flowering by the ship date.

Most growers today purchase case-cooled bulbs from their suppliers to ease their workload. When you purchase a case-cooled product you assume that the bulbs have been treated appropriately and that the crop will flower successfully and on time. To ensure that Easter lilies flower on time, growers often use "insurance" lighting with Easter lilies to ensure that the vernalization needs of the crop have been met. When Easter lily bulbs have not received at least six weeks or 1,000 hours of cooling the forcing time or days to flower increases significantly. Most growers use a forcing schedule of about 110 days with bulbs that have been case-cooled for six weeks. If inadequate case cooling has occurred and no insurance lighting has been utilized it may take up to 86 additional days for Easter lilies to flower which pushes their bloom time well past the Easter shipping date.

Easter lilies are susceptible to a few pest and disease issues, but the most serious issue observed in Pennsylvania greenhouses is basal rot which is caused by the fungus Fusarium oxysporum f. sp. lilii. The fungus that causes basal rot of lily bulbs is long-lived and can survive outdoors in production fields for many years. Lily bulbs grown in fields with a history of Fusarium oxysporum f. sp. lilii can become infected and may inadvertently spread the pathogen to adjacent uninfected lily bulbs when bulbs are close to each other (like in case cooling).

As per the Pacific Northwest Plant Disease Management Handbook regarding lily basal rot, initial infection occurs just behind the root cap. As the disease progresses a severe root rot occurs along with the destruction of the basal plate. A chocolate or bluish-gray-colored rot that extends from the basal plate into the scales is observed. Bulbs with significant disease progression will fall apart upon digging in the field because the disease causes the scales to detach from the basal plate.

Above-ground symptoms of lily basal rot include stunting, premature yellowing of the foliage, and senescence. Flower buds also may fail to open or may appear wilted. In one Pennsylvania greenhouse, Easter lily bulbs infected with lily basal rot were very stunted in appearance and appeared to be declining despite the grower's prompt interventions with chemical fungicides and his use of bio-fungicides immediately after planting.

Cultural control methods promoted by the authors of the Pacific Plant Handbook suggest that upon receiving lily bulbs they should be inspected. All bulbs that have a chocolate color rot at the base of the scales should be discarded immediately. Elevated fertility (high nitrogen) can cause an exacerbation of this disease so low nitrogen fertilizers should be utilized with lilies in both greenhouse and field settings. Some plant pathologists recommend that lily bulbs be soaked in an appropriately labeled fungicide mixture before planting. Some commercial fungicide products are labeled for this specific use.

Bulb mites are frequently considered a secondary pest of lily bulbs, but active infestations can cause plants to become quite stunted. Other observed symptoms can include yellowing leaves, poor or no development of flower stalks, and flower abortion. Bulb mites feed on the scales and outer plant tissues of the bulb. Wounds created by bulb mite feeding can provide an ideal entry site for pathogens like Fusarium oxysporum f. sp. lilii and other soil-borne diseases. Unfortunately, there are no miticides currently registered for controlling bulb mites.

Left: Stunted Easter lily infected with lily basal rot, photo: Tom Ford, Penn State. Right: Bulb mite found in Easter lily bulb tissues, photo: Dr. Sara May, Plant Disease Clinic Director, The Pennsylvania State University.