Allen D. Owings, Ferrin, Donald M. | 9/12/2011 4:24:29 AM
Entomosporium leaf spot, caused by the fungus Entomosporium mespili (formerly E. maculatum), is a common disease of various woody ornamentals in the family Rosaceae. In Louisiana landscapes, however, it is most commonly a problem on Indian hawthorn (Raphiolepis indica) and red tip photinia (Photinia fraseri).
Initial symptoms are the appearance of circular, reddish to reddish-purple spots on the new foliage that quickly develop light gray to dark gray centers. As these lesions continue to develop, a chlorotic halo may form around them, the centers of the lesions become darker and sunken, and masses of cream-colored spores may be evident in the darkened tissues. Part of or the entire leaf may then turn red. Defoliation of severely diseased leaves often follows.
The pathogen survives in infected leaves on the plant or on the soil beneath the plant, and spores are dispersed by splashing water from rainfall or irrigation. Water on the leaves is required for infection to occur. Young, expanding leaves are most susceptible to infection, and disease develops most rapidly during the cool, wet weather of spring and fall.
Management of Entomosporium leaf spot relies on the combined use of cultural practices, resistant varieties and the timely applications of fungicides. Since disease development requires that the foliage be wet, avoid dense plantings of susceptible hosts in locations with limited airflow. Selective pruning of individual branches will help increase air movement within the plant canopy and promote more rapid drying of the foliage. In addition, practicing good sanitation by removing infected leaves from the plants and raking up the leaves on the ground and discarding them will help to lower the amount of inoculum available for dispersal.
Choose resistant varieties when establishing a new planting, but also remember resistance does not imply immunity. Varieties that have some resistance to leaf spot include Eleanor Tabor (light pink), Sonata Spring (white), Snow White or Snow (white) and Clara (white).
Several fungicides can be helpful in the management of Entomosporium leaf spot, including products with chlorothalonil, myclobutanil, propiconazole or tebuconazole as the active ingredient. Begin fungicide applications as soon as new growth is evident during spring and make repeat applications every 10 to 14 days until hot weather sets in. Additional applications may be necessary during fall if weather conditions are suitable for disease development.