Resistance of 19 cultivars of Indian hawthorn (R. umbellata and R. × delacourii) to the diseases Entomosporium leaf spot (Entomosporiummespili), fireblight (Erwinia amylovora), and anthracnose (Colletotrichium gloeosporioides) was evaluated in a simulated landscape planting in Brewton, AL. Although symptoms of Entomosporium leaf spot were observed each year on the foliage of all cultivars, significant differences in disease severity were noted. Over the four-year test period, the lowest level of leaf spotting and premature leaf shed was consistently seen on Indian Princess® and Olivia™. Significant differences in the susceptibility of Indian hawthorn cultivars to fireblight, particularly in 1997 and 1998, were also noted. ‘Janice’ and ‘Jack Evans’, which proved particularly susceptible to this disease, resulted in the death on nearly all plants. In those same years, minor fireblight damage was also seen on Olivia™. Noticeable anthracnose-induced leaf damage and premature defoliation was recorded in 1997 only on Majestic Beauty®. Among the cultivars of Indian hawthorn screened, Indian Princess® suffered the least damage due to Entomosporium leaf spot, fireblight, and anthracnose over the four-year trial period. Olivia™ has excellent resistance to Entomosporium leaf spot but may prove sensitive to fireblight.
2Professor, Department of Entomology and Plant Pathology.
3Superintendent, Brewton Experiment Field.
4Superintendent, Ornamental Horticulture Substation.
5Professor, Department of Horticulture.