Erik A. Draper, James A. Chatfield, Kenneth C. Cochran, Peter W. Bristol, and Charles F. Tubesing
Crabapples in a replicated plot at the Secrest Arboretum of The Ohio State University's Ohio Agricultural Research and Development Center were evaluated for apple scab three times in 1998. Seventeen of the selections had no scab at any of the three ratings in 1998. Fourteen of the selections had scab that resulted in significant negative effect on aesthetics on at least one of the ratings.
Fifteen of the crabapples were removed from the plot in 1998 due to poor overall aesthetics over the past five years, and the summaries of scab ratings for these crabapples are reported. Scab ratings for the past six years are reported for the remaining 27 selections, and ratings for 14 newer plantings are averaged for the past two years.
Other diseases noted included bacterial fireblight, frogeye leaf spot, sooty blotch, and flyspeck.
Apple scab (pathogen: Venturia inaequalis) is a major fungal disease problem of many crabapple species (Malus spp). Although it generally is not a major health problem for the tree, it can severely impact ornamental effect and the marketability of highly susceptible crabapples.
Symptoms of apple scab on crabapple include olive to gray to brown to black spots on foliage, yellowing and discoloration of foliage, leaf drop, and scabby lesions on fruits. Apple scab can be effectively controlled with a fungicide spray program, and certain cultural and sanitary practices (thinning to avoid dense canopies, cleanup of leaves at the end of the season) are also beneficial for control.
However, the best method for control of apple scab is through the use of genetically resistant crabapple selections. The evaluations presented here are the latest in a series of apple scab evaluations for Ohio (1-3).
The authors emphasize that apple scab in particular and diseases and pests in general are not the only consideration relative to crabapple effectiveness in the landscape. This is the rationale for the inception of more comprehensive evaluations of a number of different aesthetic criteria. These include fruit, flower, and foliage features; plant texture and shape; and disease and pest problems. These are reported in a series of publications from data collected in the Secrest plot (4-7). The comprehensive crabapple evaluations at Secrest are a continuing project and are being expanded to include a second plot with additional selections.
Forty-one crabapples in the replicated crabapple plot at Secrest Arboretum were rated for apple scab disease on June 9, 1998; July 24, 1998; and August 20, 1998. This plot is in a completely randomized design with three replications of each crabapple selection (except for M. zumi 'Calocarpa,' with two surviving replicates). The plot was planted in 1984 and is not treated with fungicides or insecticides.
Apple scab evaluations were based on the following rating system:
Scab on crabapple fruits was factored into the overall scab ratings.
1. Chatfield, J. A. and Draper, E. A. 1995. Evaluation of crabapples for apple scab at the Secrest Arboretum in Wooster, Ohio: 1993-1994. Ornamental Plants: A Summary of Research 1993-1994. Special Circular 142. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 10-12.
2. Chatfield, J. A. and Draper, E. A. 1996. Evaluation of crabapples for apple scab at the Secrest Arboretum in Wooster, Ohio: 1995. Ornamental Plants: A Summary of Research, 1993-1994. Special Circular 142. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 22-26.
3. Draper, E. A., Chatfield, J. A., Cochran, K. D., Bristol, P. W. and Tubesing, C. E. 1997. Evaluation of crabapples for diseases at the Secrest Arboretum in Wooster, Ohio: 1996. Ornamental Plants: A Summary of Research, 1997. Special Circular 154. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 35-40.
4. Draper, E. A. and Chatfield, J. A. 1995. Aesthetic evaluation of crabapples at Secrest Arboretum in Wooster, Ohio: 1993-1994. Ornamental Plants: A Summary of Research, 1993-1994. Special Circular 142. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 4-9
5. Draper, E. A., Chatfield, J. A., Cochran, K. D., Bristol, P. W., and Allen, D. E. 1998. Comprehensive aesthetic evaluations of crabapples at Secrest Arboretum in Wooster, Ohio: 1993-1997. Ornamental Plants: Annual Reports and Research Reviews. 1998. Special Circular 157. Ohio Agricultural Research and Development Center. The Ohio State University. pp. 83-94.
6. Chatfield, J. A., Draper, E. A., and Cochran, K. D. 1996. Comprehensive aesthetic evaluations of crabapples in Ohio: 1993-1995. Malus: International Ornamental Crabapple Bulletin. 10(1) 5-16.
7. Draper, E. A., and Chatfield, J. A. 1996. Magic of Malus. American Nurseryman. August 15, 1996. 184 (4) pp.
| Table 1. Apple Scab Ratings for Crabapple Selections at Secrest Arboretum (6-9-98, 7-24-98, 8-20-98), and the Average Rating for Secrest Arboretum from 1993-1998. | ||||
|---|---|---|---|---|
| Crabapple | Secrest 6-9-98 | Secrest 7-24-98 | Secrest 8-20-98 | Secrest 1993-98 |
| M. baccata 'Jackii' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Beverly' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Bob White' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'David' | 1.0 | 1.0 | 1.0 | 0.9 |
| 'Dolgo' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Donald Wyman' | 2.0 | 2.0 | 3.0 | 1.3 |
| M. floribunda | 1.0 | 2.0 | 2.0 | 0.6 |
| 'Harvest Gold' | 2.3 | 3.0 | 3.3 | 2.6 |
| 'Indian Magic' | 2.0 | 2.6 | 3.0 | 2.7 |
| 'Indian Summer' | 2.0 | 2.3 | 3.0 | 2.2 |
| 'Liset' | 0.6 | 1.3 | 1.3 | 1.0 |
| 'Mary Potter' | 0.3 | 1.0 | 1.0 | 0.6 |
| 'Molten Lava' | 1.0 | 1.0 | 2.3 | 1.3 |
| 'Ormiston Roy' | 0.0 | 0.3 | 0.6 | 0.3 |
| 'Prairifire' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Professor Sprenger' | 0.0 | 0.6 | 0.6 | 0.8 |
| Crabapple | Secrest 6-9-98 | Secrest 7-24-98 | Secrest 8-20-98 | Secrest 1993-98 |
| 'Red Jade' | 1.0 | 1.0 | 1.0 | 1.2 |
| 'Red Jewel' | 0.0 | 0.3 | 0.3 | 0.1 |
| 'Red Splendor' | 1.0 | 2.0 | 3.0 | 1.5 |
| M. sargentii | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Sentinel' | 0.0 | 1.0 | 1.0 | 0.7 |
| 'Silver Moon' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Snowdrift' | 1.0 | 2.0 | 3.0 | 2.2 |
| 'Strawberry Parfait' | 0.0 | 0.0 | 0.0 | 0.1 |
| 'Sugar Tyme' | 0.3 | 0.3 | 1.0 | 0.7 |
| 'White Angel' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'White Cascade' | 1.6 | 3.0 | 3.0 | 2.2 |
| M. zumi 'Calocarpa' | 1.0 | 1.0 | 1.0 | 0.9 |
0 = No scab noted. Scab on crabapple fruits was factored into the overall scab ratings. | ||||
| Table 2. Apple Scab Ratings for Crabapple Selections at Secrest Arboretum from 1993-1997. These crabapples were discontinued in the plot due to poor overall aesthetic ratings. | |
|---|---|
| Crabapple | 1993-1997 Ratings |
| 'Adams' | 1.8 |
| 'Candied Apple' | 1.8 |
| 'Centurion' | 1.5 |
| 'Henningii' | 2.0 |
| M. Adstringens 'Hopa' | 2.9 |
| 'Profusion' | 2.8 |
| 'Radiant' | 3.1 |
| 'Ralph Shay' | 2.0 |
| 'Red Barron' | 2.0 |
| 'Robinson' | 2.5 |
| 'Royalty' | 2.0 |
| 'Ruby Luster' | 1.9 |
| 'Selkirk' | 1.7 |
| 'Velvet Pillar' | 2.8 |
| 'Winter Gold' | 2.5 |
0 = No scab noted. Scab on crabapple fruits was factored into the overall scab ratings. | |
| Table 3. Apple Scab Ratings for Crabapple Selections at Secrest Arboretum for Crabapples rated on 6-9-98, 7-24-98, and 8-20-98, and the Average Rating for Secrest Arboretum from 1997-1998. | ||||
|---|---|---|---|---|
| Crabapple | 6-9-98 | 7-24-98 | 8-20-98 | 97-98 Avg. |
| 'Adirondack' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Camelot' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Canary' | 2.3 | 2.0 | 2.0 | 2.2 |
| 'Candymint' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Glen Mills'' | 0.6 | 2.3 | 3.0 | 2.2 |
| 'Golden Raindrops' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Lancelot' | 0.0 | 0.0 | 0.0 | 0.1 |
| 'Louisa' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Narangansett' | 1.0 | 2.0 | 2.0 | 1.9 |
| 'Pink Satin' | 0.6 | 2.0 | 2.3 | 1.7 |
| 'Prairie Maid' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Purple Prince' | 0.0 | 0.0 | 0.0 | 0.0 |
| 'Silver Drift' | 0.6 | 1.3 | 1.3 | 1.1 |
| 'Sinai Fire' | 0.0 | 0.0 | 0.0 | 0.0 |
0 = No scab noted. Scab on crabapple fruits was factored into the overall scab ratings. | ||||
Erik A. Draper, Ohio State University Extension, Geauga County; James A. Chatfield, Ohio State University Extension, Northeast District/Department of Horticulture and Crop Science, The Ohio State University; Kenneth C. Cochran, Secrest Arboretum of the Ohio Agricultural Research and Development Center/Ohio State University Agricultural Technical Institute; Peter W. Bristol, Holden Arboretum; and Charles F. Tubesing, Holden Arboretum.