Susceptibility of Indian Hawthorn Cultivars to Fireblight, Anthracnose, and Entomosporium Leaf Spot

 Austin K. Hagan, J. Randy Akridge, John W. Olive, and Ken Tilt

ndian hawthorn (Raphiolepis indica), with its dark-green foliage, mounded canopy, and compact growth habit, is a fixture in Alabama’s residential and commercial landscapes. In the nursery and landscape, Entomosporium leaf spot, which is caused by the fungus Entomosporium mespili, is the most common and damaging disease of Indian hawthorn. Unfortunately, Entomosporium leaf spot is not the only damaging disease on Indian hawthorn. Destructive outbreaks of fireblight, a bacterial disease caused by Erwinia amylovora, have also been seen on container stock in the nursery and landscape. A third foliar disease, anthracnose, caused by the fungus Colletotrichum gloeosporides, may also damage selected Indian hawthorn cultivars.

In recent years, a number of new cultivars of Indian hawthorn have been released by the nursery industry. Previous AAES reports have documented that cultivars of Indian hawthorn differ significantly in their susceptibility to Entomosporium leaf spot. A few suffer little more than light spotting of the lower leaves, while others may be completely defoliated. The reaction of cultivars of Indian hawthorn to the diseases fireblight and anthracnose is, however, unknown. This report summarizes data collected in 1997 and 1998 concerning the reaction of selected cultivars in a simulated landscape planting to the diseases Entomosporium leaf spot, fireblight, and anthracnose.

In March 1994, the initial planting of dwarf and standard Indian hawthorn cultivars was established in a simulated landscape planting at the Brewton Experiment Field near Brewton, Alabama. In March 1995, ‘Snow White’ and ‘Rosalinda’, which are a dwarf and standard form, respectively, were added to the study. ‘Bay Breeze’ and ‘Becky Lynn’, both dwarf cultivars, were planted in the early spring of 1996 and 1998, respectively.

Soil pH and fertility in the beds were adjusted according to the results of a soil fertility assay. The beds were mulched with aged pine bark and watered as needed using a drip irrigation system. Twice each spring, approximately 0.5 cup of Osmocote 17-7-12 was uniformly distributed around each plant. A tank mixture of 1 pound of Gallery 75DF and 2 quarts of Surflan AS T/O were broadcast over the beds on a per acre basis to control annual weeds. Hand weeding and directed applications of recommended rates of Roundup or MSMA were used to control escaped weeds and invading centipedegrass. On May 19, 1997 and May 13, 1998, Entomosporium leaf spot was rated on a scale of 1 to 5 where 1 = no disease, 2 = 1 to 25 %, 3 = 26 to 50%, 4 = 50 to 75%, and 5 = 76 to 100% of leaves diseased or defoliated. On June 29, 1997 and August 5, 1998, fireblight severity was assessed on a scale of 0 to 4 where 0 = no disease, 1 = one or few blighted branch tips, 2 = numerous branch tips blighted and a few scaffold branches killed, 3 = major portion of bush killed, and 4 = bush dead. Anthracnose ratings were taken on June 29, 1997 and August 5, 1998 using the scale previously described for Entomosporium leaf spot.

Substantial differences in severity of Entomosporium leaf spot were noted in 1997 and 1998 among the cultivars screened. In both years, damage on individual cultivars ranged from unobtrusive spotting of a few scattered leaves to near complete defoliation (see table). Since the study was started in 1994, the disease ratings of some leaf spot-resistant cultivars, particularly for ‘Dwarf Yedda’ have gradually worsened.

Ratings for Entomosporium Leaf Spot, Fireblight, and Anthrancnose on Cultivars
of Indian Hawthorn, 1997-1998
Cultivar Leaf spot ratings1 Fireblight ratings2 Anthracnose
  1997 1998 1997 1998 1997
Heather 4.0 4.8 0.2 0.1 1.0
Springtime 4.7 4.0 0.1 0.0 1.0
Pinkie 4.2 4.5 0.1 0.1 1.0
Enchantress 4.5 4.3 0.3 0.0 1.0
Harbinger of Spring 4.6 4.4 0.1 0.1 1.0
White Enchantress 4.2 4.0 0.0 0.1 1.0
Spring Rapture 4.0 4.5 0.0 0.3 1.0
Bay Breeze 3.6 4.8 0.0 0.1 1.0
Clara 3.0 3.5 0.1 0.0 1.0
Rosalinda 3.0 3.3 0.1 0.0 1.3
Majestic Beauty 3.0 3.5 0.6 0.0 2.7
Snow White 3.2 3.3 0.0 0.1 1.0
Jack Evans 3.0 Dead 4.0 Dead 1.0
Becky Lynn ---3 4.3 --- 0.1 ---
Dwarf Yedda 2.8 3.5 0.0 0.0 1.0
Janice 2.6 Dead 3.7 Dead 1.0
Eleanor Tabor 2.5 3.3 0.2 0.0 1.0
Indian Princess 2.3 2.7 0.2 0.1 1.0
Olivia 2.0 2.3 0.7 1.1 1.0
1Entomosporium leaf spot and anthracnose were assessed on a scale of 1 to 5 where 1 = no disease; 2 = 1 to 25%; 3 = 26 to 50%; 3 = 51- 75%; 4 = 76 to 100% of leaves diseased or defoliated.
2Fireblight was rated on a 0 to 4 scale where 0 = no disease; 1 = one to several spurs or shoot tips dead; 2 = numerous branch tips blighted and a few scaffold branches killed; 3 = major portion of bush killed; and 4 = bush dead.
3‘Becky Lynn’ was planted in March 1998.

In 1997, light to moderate spotting of the foliage with a very low level of disease-related leaf shed (disease ratings of 2.0 to 2.6) were noted for ‘Olivia’, ‘Indian Princess’, ‘Eleanor Tabor’, and ‘Janice’ (see table). Of these, ‘Olivia’ visually had the least spotting of the foliage and no defoliation. Nearly all remaining cultivars suffered moderate to heavy spotting of the foliage along with considerable to near total defoliation. With disease ratings higher than 4.0, ‘Springtime’, ‘Enchantress’, ‘Harbinger of Spring’, ‘Pinkie’, and ‘White Enchantress’ proved extremely sensitive to Entomosporium leaf spot.

Disease ratings for Entomosporium leaf spot taken in 1998 were higher, particularly for the leaf spot resistant cultivars ‘Olivia’, ‘Indian Princess’, ‘Dwarf Yedda’, and ‘Eleanor Tabor’, as compared with levels seen in the previous year. Heavy and frequent rainfall in January through March is largely responsible for this increase in leaf spot related damage. ‘Olivia’ and ‘Indian Princess’, as indicated by disease ratings of 2.3 to 2.7, suffered only light spotting of the leaves (see table). Spotting of the lower leaves and premature defoliation was heavier on ‘Dwarf Yedda’ and ‘Eleanor Tabor’ than had been seen in 1998. Like the previous year, considerable spotting of the leaves and severe to near complete defoliation was noted on many of the remaining cultivars of Indian hawthorn.

A blossom blight and shoot dieback, which typically is associated with the disease fireblight, was first noted on selected cultivars in mid-May 1997. Within 2 months of the onset of symptoms, the cultivars ‘Janice’ and ‘Jack Evans’ had succumbed to this disease (Table 1). Some fireblight-related shoot and limb dieback was also seen on ‘Olivia’ and ‘Majestic Beauty’. Although some blossom blight was seen on a few cultivars, none suffered significant fireblight-related damage.

In 1998, significant limb dieback was limited to the ‘Olivia’ (see table). On 10 additional cultivars, death of an individual spur(s) or lateral shoot(s) was seen but damage was light and unobtrusive.

Anthracnose, which typically appears in late spring or early summer, causes some spotting of the leaves and early leaf shed. Concentric rings of light and dark tissue give the large leaf spots, which may be an inch or more in diameter, a ‘target spot’ appearance. In 1997, disease development was limited to the two standard cultivars ‘Majestic Beauty’ and ‘Rosalinda’ (see table). Of these, the heaviest damage was recorded on ‘Majestic Beauty’. Due to unusually dry weather from April through August, no symptoms of anthracnose were noted in 1998 on any cultivars of Indian hawthorn.

In addition to Entomosporium leaf spot, fireblight and anthracnose are also potential threats in the nursery and landscape to the health and beauty of Indian hawthorn. Of these two diseases, fireblight is most likely to cause significant damage to Indian hawthorn, particularly in the nursery. As a result, the cultivars ‘Janice’ and ‘Jack Evans’ that are very susceptible to fireblight,would be poor choices to produce in a nursery or install in landscapes. Dwarf cultivars ‘Eleanor Tabor’ and ‘Indian Princess’ suffered the least damage from all the above diseases. ‘Olivia’, which has good resistance to Entomosporium leaf spot, proved somewhat sensitive to fireblight. The disease-resistant Indian hawthorn cultivars noted above can be produced in a nursery with few if any costly pesticide treatments. Also, they would be excellent choices for the low maintenance landscapes favored by most landscaper managers and homeowners. On the other hand, leaf spot-susceptible cultivars such as ‘Heather’, ‘Springtime’, ‘Pinkie’, ‘Harbinger of Spring’, ‘White Enchantress’, and ‘Enchantress’, which consistently suffered heavy defoliation in late winter and early spring, were unattractive and unthrifty. Such leaf spot-susceptible cultivars would require frequent fungicide applications in order to maintain their appearance and health.

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