Buckeye Yard and Garden onLine

Dave Dyke reported that he made a site visit to a greenhouse several weeks ago to offer help with a Boston fern problem. The visit proved interesting in illustrating the challenge in diagnosing multiple problems occurring at the same time on the same plant species.

The grower had reported that "little green worms" were eating the tips of the ferns, causing so much damage the ferns had to be cut completely back. However, when the ferns started to grow back … well … many didn't. Healthy plants should have been able to recover from caterpillar damage.

The caterpillars were identified by Luis Canas (OSU Entomology) as FLORIDA FERN CATERPILLARS (Callopistria floridensis). They appear to be a developing problem in greenhouses in Ohio. The caterpillar can present an identification challenge since they have five color forms: a light-green form; a green form with an upper white line and a lower black line down each side; a form with the upper and lower white and black lines down each side plus black spots on the back and upper sides; a velvety dark-striped or black form; and a velvety dark-striped or black form with a white line down each side. Sometimes green worms occur with thin, pale, yellow stripes on the back, and bold, white stripes on each side.

During the visit, Dave also observed symptoms on the ferns that were clearly not produced by the caterpillars. Many of the ferns had browning at the base, and browning and loss of lower leaflets. He also noted that pots on one end of the bench were uniformly worse than those on the other end. Although he suspected a problem with inconsistent watering, his first step was to eliminate a plant pathogen as the culprit, so he sent samples to the C. Wayne Ellet Plant and Pest Diagnostic Clinic (CWEPPDC).

The CWEPPDC found no pathogens associated with the damaged ferns which focused Dave's diagnostic attention on a watering issue. The fact that lower leaflets were browned but leaflets above looked fine on many plants indicated that the pots had been allowed to become too dry at some point, but were subsequently given adequate water. When questioned, the grower confirmed that the plants had indeed been allowed to become very dry after they had been cut back. Although the CWEPPDC did not isolate any pathogens, they did suggest that high salts may have produced the symptoms. Of course, the salt concentration in a container is going to rise as it gets drier. Case solved.

For more information, see:

• Florida Fern Caterpillar