Apple scab pressure was high at the Secrest Arboretum of the Ohio State University’s Ohio Agricultural Research and Development Center in 2004, as wet spring and early summer weather provided multiple infection periods for the Venturia inaequalis pathogen. Yet, even under this considerable disease pressure, 24 of the 64 taxa showed no evidence of apple scab in 2004, and a total of 30 never received a rating that exceeded 1 (no aesthetic impact) on any evaluation date. Nineteen taxa received a rating of 3 or higher on at least one date in 2004, indicating substantial defoliation and aesthetic impact (Table 1).
Sixty-three crabapple taxa were planted in 1997-1998 at OARDC’s Secrest Arboretum in Wooster, Ohio, in a completely randomized design. One taxon, ‘Cardinal,’ was planted in 2003. There are five replicate plants for most but not all taxa, though fewer replicates exist currently due to a variety of factors, including inadequate original numbers (e.g., ‘Hamlet’), death due to fireblight (e.g., ‘Golden Raindrops’), and other attrition such as deer damage.
Plants are mulched with composted yard waste and were irrigated as needed during the year of transplanting. Weeds are controlled with spot applications of glyphosate. On June 9, July 16, and August 18, 2004, all trees were rated on a scale of 0 to 5, with 0 = no scab observed; 1 = less than 5% of leaves affected and no aesthetic impact; 2 = 5 to 20% of leaves affected, with some yellowing but little or no defoliation, moderate aesthetic impact; 3 = 20 to 50% of leaves affected, significant defoliation and/or leaf yellowing, substantial aesthetic impact; 4 = 50 to 80% of leaves affected, severe foliar discoloration and defoliation, severe aesthetic impact; and 5 = 80 to 100% of foliage affected, with 90 to 100% defoliation.
Results of the 2004 trials are presented in Table 1.
Results over the past several years show that, for some taxa, scab incidence is changing, presumably due to the development of new races of the Venturia inaequalis pathogen.
Apple scab was not observed on ‘Prairifire’ crabapple for several decades at Secrest until 2000 and 2001 when it first was noted, though at very low levels. Now in 2004, scab on ‘Prairifire’ is more noticeable, with its rating of 2 indicating moderate aesthetic impact on all replicates for the first time.
Scab was found on ‘Bob White’ in 2004 for the first time, though only on one replicate and only to a minor extent.
| Table 1. Apple Scab at Secrest Arboretum in Wooster, Ohio, in 2004. | ||||
| Crabapple Taxon | Aug 18 | Jul 16 | Jun 9 | No. of Reps |
| ‘Adirondack’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Callaway’ | 0.00 | 0.00 | 0.00 | 4 |
| ‘Camelot’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Canterbury’ | 0.00 | 0.00 | 0.00 | 4 |
| ‘Cardinal’ | 0.00 | 0.00 | 0.00 | 3 |
| ‘Cinderella’ | 0.00 | 0.00 | 0.00 | 4 |
| ‘Dolgo’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Excalibur’ | 0.00 | 0.00 | 0.00 | 4 |
| ‘Firebird’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Foxfire’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Golden Raindrops’ | 0.00 | 0.00 | 0.00 | 2 |
| ‘Hamlet’ | 0.00 | 0.00 | 0.00 | 2 |
| ‘Holiday Gold’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Jackii’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Lancelot’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Lollipop’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Louisa’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Prairie Maid’ | 0.00 | 0.00 | 0.20 | 5 |
| ‘Rawhide’ | 0.00 | 0.00 | 0.00 | 4 |
| ‘Red Jewel’ | 0.00 | 0.00 | 0.00 | 5 |
| M. sargentii | 0.00 | 0.00 | 0.00 | 5 |
| ‘Silver Moon’ | 0.00 | 0.00 | 0.00 | 4 |
| ‘Sinai Fire’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Strawberry Parfait’ | 0.00 | 0.00 | 0.00 | 4 |
| ‘Tina’ | 0.00 | 0.00 | 0.00 | 5 |
| ‘Guinevere’ | 0.20 | 0.20 | 0.20 | 5 |
| ‘Bob White’ | 0.40 | 0.40 | 0.60 | 4 |
| ‘King Arthur’ | 0.50 | 0.00 | 0.00 | 2 |
| ‘Brandywine’ | 1.00 | 1.00 | 1.00 | 4 |
| ‘David’ | 1.00 | 1.00 | 1.00 | 4 |
| ‘Candymint’ | 1.40 | 1.00 | 0.40 | 5 |
| ‘Purple Prince’ | 1.40 | 1.00 | 0.80 | 5 |
| ‘Pink Princess’ | 1.50 | 1.00 | 0.50 | 3 |
| ‘Coralburst’ | 2.00 | 2.00 | 1.00 | 5 |
| ‘Manbeck Weeper’ | 2.00 | 1.50 | 1.50 | 5 |
| ‘Mary Potter’ | 2.00 | 1.00 | 0.75 | 4 |
| ‘Prairifire’ | 2.00 | 1.60 | 0.80 | 5 |
| ‘Professor Sprenger’ | 2.00 | 1.50 | 1.25 | 4 |
| ‘Red Jade’ | 2.20 | 2.40 | 1.00 | 4 |
| ‘Silver Drift’ | 2.20 | 2.00 | 1.00 | 5 |
| ‘Sugar Tyme’ | 2.20 | 2.00 | 1.00 | 5 |
| ‘Doubloons’ | 2.40 | 2.00 | 1.00 | 5 |
| ‘Molten Lava’ | 2.40 | 2.00 | 1.00 | 5 |
| ‘American Salute’ | 2.80 | 1.80 | 0.80 | 5 |
| ‘Canary’ | 2.80 | 2.00 | 1.60 | 5 |
| ‘Harvest Gold’ | 2.80 | 3.00 | 2.80 | 5 |
| ‘Adams’ | 3.00 | 3.00 | 2.60 | 5 |
| ‘Donald Wyman’ | 3.00 | 2.00 | 1.80 | 5 |
| ‘Red Splendor’ | 3.00 | 2.40 | 1.00 | 5 |
| ‘Sentinel’ | 3.00 | 2.00 | 1.00 | 5 |
| ‘Jewelberry’ | 3.50 | 3.00 | 1.50 | 4 |
| ‘Royal Fountain’ | 3.60 | 2.80 | 1.80 | 5 |
| ‘Indian Magic’ | 3.75 | 3.00 | 2.75 | 4 |
| ‘Spring Snow’ | 4.00 | 2.80 | 2.00 | 5 |
| ‘Snowdrift’ | 4.00 | 3.40 | 2.80 | 5 |
| ‘White Cascade’ | 4.00 | 3.00 | 3.00 | 5 |
| M. floribunda | 4.20 | 3.20 | 3.00 | 5 |
| ‘Weeping Candied Apple’ | 4.20 | 4.00 | 3.00 | 5 |
| ‘American Spirit’ | 4.25 | 3.00 | 2.00 | 4 |
| ‘Thunderchild’ | 4.60 | 3.60 | 3.00 | 5 |
| ‘Royal Scepter’ | 4.75 | 3.20 | 2.00 | 5 |
| ‘American Masterpiece’ | 4.80 | 4.00 | 3.00 | 5 |
| ‘Pink Satin’ | 4.80 | 4.00 | 2.40 | 5 |
| ‘American Triumph’ | 4.80 | 3.40 | 2.40 | 5 |
| * 0 = no scab observed; 1 = less than 5% of leaves affected and no aesthetic impact; 2 = 5 to 20% of leaves affected, with some yellowing but little or no defoliation, moderate aesthetic impact; 3 = 20 to 50% of leaves affected, significant defoliation and/or leaf yellowing, substantial aesthetic impact; 4 = 50 to 80% of leaves affected, severe foliar discoloration and defoliation, severe aesthetic impact; and 5 = 80 to 100% of foliage affected, with 90 to 100% defoliation. ** Means in a column with the same letter are not significantly different (LSD test, p<0.05). | ||||
Draper, E. A., Chatfield, J. A., and Cochran, K. D., 2004. Apple Scab on Crabapple at Secrest Arboretum: 2003. In: Ornamental Plants: Annual Reports and Research Reviews, 2003. Special Circular 193: 135-139. The Ohio State University, Ohio Agricultural Research and Development Center.
Draper, E. A., Chatfield, J. A., and Cochran, K. D., 2004. 10 Crabapples to Know, Show, and Grow. In: Ornamental Plants: Annual Reports and Research Reviews, 2003. Special Circular 193: 170-180. The Ohio State University, Ohio Agricultural Research and Development Center.
Draper, E. A., Chatfield, J. A., and Cochran, K. D. 2003.A collection of crabapple knowledge from Secrest Arboretum: 1993-2002. In: Ornamental Plants: Annual Reports and Research Reviews. Special Circular 189: 119-138. The Ohio State University, Ohio Agricultural Research and Development Center.
Chatfield, J. A., Draper, E. A., Herms, D. A., and Cochran, K. D. 2002. Apple scab on crabapples at Secrest Arboretum: 2001.In: Ornamental Plants: Annual Reports and Research Reviews. Special Circular 186: 93-96. The Ohio State University, Ohio Agricultural Research and Development Center.
Fiala, Fr. John L. 1994. Flowering Crabapples — The Genus Malus.Timber Press, Portland, Oregon.
The authors would like to thank Ohio nurseries, including Lake County Nursery, Klyn Nurseries, Sunleaf Nursery, Willoway Nursery, and others for support and plant material for this project as well as Bailey Nurseries of Minnesota and J. Frank Schmidt Nursery of Oregon for plant material and participation in the International Ornamental Crabapple Society National Crabapple Evaluation Project. We would also like to thank the Secrest Arboretum of the Ohio Agricultural Research and Development Center of Ohio State University, especially the always-professional and always-helpful grounds department headed by James Karcher.
Erik A. Draper, Ohio State University Extension, Geauga County; James A. Chatfield, Ohio State University Extension Center at Wooster, Horticulture and Crop Science; Daniel A. Herms, Ohio Agricultural Research and Development Center, Entomology; and Kenneth D. Cochran, Secrest Arboretum, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster, Ohio.