Leaf spot, caused by the fungus Entomosporium maculatum, is a widespread and destructive disease of red tip (Photinia fraseri). Many people know this and red tips are not used much anymore. However, few know, but more are finding out that this disease is also widespread and destructive to indian hawthorn (Rhaphiolepis species). This disease is most damaging to plants in the landscape and nurseries during periods of cool, wet weather and when active growth is occurring.
Tiny, circular, bright red spots on both the upper and lower surfaces of young expanding leaves are the first symptoms of Entomosporium leaf spot. Numerous small spots may merge into large maroon blotches on heavily diseased leaves. Leaf spots on mature leaves have ash brown to light gray centers with a distinctive deep red to maroon border. Tiny black specks can often be observed in the center of each leaf spot. Spots similar to those on the leaves can develop on leaf petioles and tender stem growth during prolonged periods of cool, wet weather.
Low levels of leaf spot usually cause little more than cosmetic damage but maintain a source of spores for future infections. Severe infections, however, often result in early and heavy leaf drop. Heavy leaf drop severely reduces the landscape value of Indian hawthorn and can cause plant death. Some cultivars of India hawthorn are as severely affected as red tip.
Spots on the leaves and young shoots are important in the survival of the Entomosporium leaf spot fungus. Fallen, diseased leaves are less important sources of the fungus. Masses of spores are released during periods of wet weather from the fungal spore producing structures in the center of the spots from late winter through much of the year except during the hot periods of summer. These spores are spread to healthy foliage by a combination of splashing water and wind. New leaf spot symptoms appear within 10-14 days after a wet infection period.
For the landscape, red tips are avoided since none are resistant to the disease. Japanese cleyera is a good substitute. There are some Indian hawthorn cultivars that have shown resistance to this point. Resistant varieties at present time include Eleanor Tabor, Indian Princess, Gulf Green, Betsy, Blueberry Muffin, Georgia Petite, Olivia, and Snow White. Purchase plants showing no leaf spot symptoms. Isolated healthy plants or hedges can often remain healthy as the spores are only splashed over short distances. Space plants to improve the air movement around the plants and promote rapid drying of leaf surfaces. If it is necessary to irrigate the plants, do not wet the foliage or irrigate in midday to reduce the period of time foliage remains wet. If possible, remove fallen diseased leaves. Do not water or fertilize plants any more than necessary to avoid promoting excess new growth. Also, reduce pruning during the summer, which promotes continual new growth. Severely defoliated plants may need to be pruned heavily to have a small, easier to spray plant, to reduce the source of spores and improve air movement. It may be necessary to remove severely diseased plants and replace them with another plant species that is not susceptible to leaf spot. Most other common landscape shrubs are not susceptible to the disease.
Several fungicides may also be help in the management of leaf spot in the landscape. Products containing chlorothalonil, myclobutanil, propiconazole, or triforene can be used according to label instructions.
This disease is very difficult to control after plants are severely infected. During extended cool, wet periods, protective sprays may be necessary. Where leaf spot is a problem, applications of one of the above fungicides should begin as new growth starts in the spring with additional sprays at 10 – 14 day intervals until mid-June. Make applications at 10-day intervals during cool, wet periods and at 14-day intervals during drier periods. Fungicide applications should not be necessary during hot, dry periods. It may also be helpful to make 3-4 applications from mid-October to late November if wet weather prevails.
A great way to avoid this heavy use of pesticides is to remove infected plants and replace with a flowering evergreen that does not get the disease. Dwarf cultivars of glossy abelia work well in full sun situations that Indian hawthorn like. They flower later, starting in May but continue to flower through October. Good cultivars I have grown include ‘Little Richard’, ‘Sherwood’, Confetti TM, ‘Kaleidoscope’, and ‘Sunrise’.
If you have questions about gardening, landscaping, lawns, trees, or whatever is going on with plants in your yard give the Pitt County Extension Master Gardener Volunteers a call at 902-1705 or email them at firstname.lastname@example.org. Find out more about Extension, the Pitt County Arboretum, and gardening in Pitt County by visiting http://pitt.ces.ncsu.edu or www.pittcountyarboretum.blogspot.com .