Controlling Entomosporium Leaf Spot on Woody Ornamentals

Symptoms. Tiny circular, bright red spots on both the upper and lower surfaces of young expanding leaves are the first sign of Entomosporium leafspot. Large purple to maroon blotches, much darker than the surrounding healthy tissue, may be found on heavily diseased young leaves of photinia. On indian hawthorn, these blotches are bright red. Leaf spots on the mature leaves of most host plants have ash brown to gray centers with a distinctive deep red to maroon margin, while those on pears have a thin brown margin.

On heavily diseased leaves, the spots merge, forming large, irregular blotches. Tiny black specks, fruiting bodies of the Entomosporium leaf spot fungus, are often found in the center of each leaf spot. Spots similar to those on the leaves often develop on leaf petioles and tender shoots. Light infections usually cause little more than cosmetic damage, while severe infections often result in early and heavy leaf drop. Severe defoliation not only slows growth but also increases plant sensitivity to environmental and cultural stresses.

Disease Cycle. Spots on the leaves, young shoots, and fallen diseased leaves are important survival sites of the Entomosporium leaf spot fungus. Masses of spores are released from the fungal fruiting bodies from late winter through much of the growing season. These spores are spread to healthy foliage by a combination of splashing water and wind. Symptoms will appear within 10 to 14 days after infection during warm, humid weather.

Typical leaf spot symptoms on red tip photinia.

In nurseries, year-round problems with Entomosporium leaf spot often result from the combination of continuous plant growth, closely spaced plants, and overhead irrigation. Disease development is more seasonal in home landscapes. Leaf spot symptoms appear mainly during the spring growth flush on the younger leaves. The wetter the spring, the more severe the spotting and shedding of leaves. Little fresh damage is usually found during the summer months because mature leaves are quite resistant to infection and hot, dry weather slows disease spread and development. In Alabama's southern counties, this disease may also be active in home landscapes during warm, humid, weather from late fall through early spring.

Control. In commercial nurseries, propagate clean plant material collected from disease-free stock plants. For the home, purchase plants showing no symptoms of Entomosporium leaf spot. Do not locate new plantings near established diseased plants. In both nurseries and landscapes, slow the spread of disease by spacing plants to improve air movement and speed evaporation of moisture from the foliage. Surface or drip irrigation is preferred to watering with overhead sprinklers. Schedule overhead irrigation between 2 and 6 a.m. or at mid-day to reduce the period of time the foliage remains wet. If possible, collect and discard fallen diseased leaves, an important source of fungal spores.

Currently, no selectons of red tip photinia are resistant to Entomosporium leaf spot. In recent trials in Alabama, the indian hawthorn cultivars, 'Dwarf Yedda', 'Olivia', 'Indian Princess', 'Snow White', and Raphiolepis. x delacourii, have shown excellent resistance to this disease. The recently released cultivar 'Eskimo' reportedly also has good leaf spot resistance. Cultivars of indian hawthorn that consistently have suffered severe leaf drop are 'Pinkie', 'Harbinger of Spring', 'Enchantress', 'Heather', 'White Enchantress', 'Springtime', and 'Spring Rapture'. The above cultivars are so sensitive to Entomosporium leaf spot that they may require routine preventive fungicide sprays to preserve their health and beauty in the landscape. No information is available concerning the reaction of cultivars of the other hosts of this disease.

Fungicides can provide effective protection from Entomosporium leaf spot. See Table 1 for a complete listing of fungicides cleared for disease control. Preventive fungicide sprays are needed all season in nurseries to ensure production of disease-free plants, whether Entomosporium leaf spot is present or not. In home landscapes, routine fungicide applications on healthy plants are rarely needed unless diseased plants are nearby. For effective protection, apply fungicides about every 10 to 14 days from the bud break until all new foliage has matured. Fungicide applications may be resumed in the fall during periods of mild weather. In nurseries, a preventive spray program should run from bud break in early spring through the first hard frost in late fall. If winter weather is unseasonably warm, fungicide applications are suggested in the southern most counties in Alabama.

On partially defoliated plants, a rigorous curative fungicide spray program is often necessary to control Entomosporium leaf spot. Weekly fungicide applications plus severe pruning to stimulate shoot development should restore the beauty of badly diseased plants. Once the plants have produced a healthy canopy of leaves, good sanitation and preventive fungicide sprays should keep the disease in check.

Indian hawthorn severely defoliated by Entomosporium leaf spot.

WOODY ORNAMENTAL

Indian Hawthorne - Raphiolepsis umbellata, R. indica, R. delacourii
Entomosporium leaf spot - Entomosporuim maculatum (syn. Fabraea maculata)

Disease Symptoms:
Symptoms on foliage are distinct circular red lesions with gray centers forming as the lesions expand. Dark specks (fruiting bodies of the fungus) may be visible within the gray centers. Cut very small pieces of the lesion and place on slide with water droplet. Macerate the tissue with a scalpel or razor blade and cover with a cover slide to find spores and fruiting bodies (acervuli) of the fungus. Spores are unusual, distinctive, and often described as "bug-like" as seen below.

Masses of cream-colored conidia are discharged from the acervuli. Acervuli are subcuticular, discoid and dark. Conidiophores are short and simple; conidia are hyaline, eguttulate, smooth, thin-walled, 4-celled, and cross-shaped, usually with three hair-like appendages.

Cultural practices are important to control Entomosporium leaf spot. Infection is favored by free moisture on the leaves. Avoid wetting the foliage when watering. Selective pruning can increase air circulation through the plant and reduce disease incidence. Severly infected leaves on the plant and those fallen on the ground shoudl be removed fromt he area and thrown away. Infection occurs primarily in the milder weather of the spring and the fall. Fungicides are most effective during this time. Refer to the Georgia Pest Control Handbook for specific fungicide recommendations. Susceptibility to leaf spot development varies by cultivar. Resistance varieties include Olivia, Eleanor Tabor, Indian Princess, Gulf Green, Georgia Petite. Susceptible varieties include Bay Breeze, Cameo, Springtime, Pinkie, Enchantress and Heather. Good plant selection will give 'permanent' control of this disese.

Compiled by:
Taft H. Eaker
Extension Homeowner IPM Specialist - Athens
University of Georgia

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