Persistent wet weather is creating conditions for Entomosporium leaf spot to make an appearance in Louisiana. Caused by the fungus Entomosporium mespili, it’s 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), says LSU AgCenter horticulturist Allen Owings.
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 the lesions develop, a yellow or white 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, and defoliation often follows.
“The pathogen survives in infected leaves on the plant or on the soil beneath the plant,” Owings says. “Spores are dispersed by splashing water from rainfall or irrigation.”
Water on the leaves is required for infection to occur. Young, growing leaves are most susceptible to infection, and disease develops most rapidly during cool, wet spring and fall weather.
Controlling Entomosporium leaf spot relies on management, resistant varieties and timely fungicide applications.
Because disease development occurs on wet foliage, avoid dense plantings of susceptible plants hosts in locations with limited airflow, Owings says.
“Selective pruning of individual branches will help increase air movement within the plant canopy and promote more rapid drying of the foliage,” he says.
In addition, practice good sanitation by removing infected leaves from the plants and raking and discarding the leaves on the ground to lower the amount of inoculum available.
“Choose resistant varieties when establishing a new planting, but also remember resistance does not imply immunity,” Owings says.
Varieties that have some resistance to leaf spot include Eleanor Tabor and Spring Sonata.
Several fungicides can be helpful in managing 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 the 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.
Got a gardening question? Write to GardenNews@agcenter.lsu.edu.