James A. Chatfield
Erik A. Draper
Kenneth D. Cochran
and Daniel A. Herms
Sixty-three crabapples in a new replicated plot at the Secrest Arboretum of The Ohio State University were evaluated for apple scab four times in 2000. Though it was a heavy year for scab at Secrest, 25 of the 63 taxa showed no evidence of apple scab in 2000, and a total of 33 never received a rating that exceeded 1 (no aesthetic impact) on any evaluation date. 'Prairifire' had never before exhibited scab in our trials at Secrest but did have some lesions in 2000. 'Red Jewel' and 'Candymint,' two cultivars that had also shown very little scab in past years, had a trace of scab in 2000. Seventeen taxa received a rating of 3 or higher on at least one date, indicating substantial defoliation and aesthetic impact.
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).
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 plots (2-3).
Sixty-three crabapple taxa were planted in 1997-1998 at the Secrest Arboretum of the Ohio Agricultural Research and Development Center (OARDC) in Wooster, Ohio, in a completely randomized design. There were five replicate plants for each taxa with the exception of 'Brandywine,' 'Canary,' 'Dolgo,' 'Indian Magic,' 'King Arthur,' and 'Royal Scepter,' for which there were four replicates, and 'Hamlet,' for which there were three. Plants were mulched with composted yard waste and irrigated as needed during the year of transplanting. Weeds were controlled with spot applications of glyphosate. On June 14, July 7, August 2, and September 7, 2000, all trees were rated on a scale of 0-5, with 0 = no scab observed; 1 = less than 5% of leaves affected and no aesthetic impact; 2 = 5-20% of leaves affected, with some yellowing but little or no defoliation, moderate aesthetic impact; 3 = 20-50% of leaves affected, significant defoliation and/or leaf yellowing, substantial aesthetic impact; 4 = 50-80% of leaves affected, severe foliar discoloration and defoliation, severe aesthetic impact; and 5 = 80-100% of foliage affected, with 90-100% defoliation.
Scab pressure was extremely high at Secrest Arboretum in 2000. In an adjacent crabapple plot, apple scab severity was greater in 2000 than in any year since ratings began in 1993. Yet, even under this considerable disease pressure, 25 of the 63 taxa showed no evidence of apple scab in 2000 and a total of 33 never received a rating that exceeded 1 (no aesthetic impact) on any evaluation date.
'Prairifire' had never before exhibited scab in our trials at Secrest but did have some lesions in 2000. 'Red Jewel' and 'Candymint,' two cultivars that had also shown very little scab at Secrest in past syears, had a trace of scab in 2000. Seventeen taxa received a rating of 3 or higher on at least one date, indicating substantial defoliation and aesthetic impact.
1. Chatfield, J. A., E. A. Draper, K. D. Cochran, P. W. Bristol, and C. F. Tubesing. 2000. Evaluation of crabapples for apple scab at the Secrest Arboretum in Wooster, Ohio: 1999. The Ohio State University, Ohio Agricultural Research and Development Center. Special Circular 173. Ornamental Plants: Annual Reports and Research Reviews, 1999. pp. 83-87.
2. Chatfield, J. A., E. A. Draper, and K. D. Cochran. 1996. Comprehensive aesthetic evaluations of crabapples in Ohio: 1993-1995. Malus: International Ornamental Crabapple Bulletin 10(1) 5-16.
3. Chatfield, J. A., E. A. Draper, K. D. Cochran, P. W. Bristol, and D. E. Allen. 1998. Comprehensive Evaluations of Crabapples at Secrest Arboretum in Wooster: 1993-1998. The Ohio State University, Ohio Agricultural Research and Development Center. Special Circular 162. Ornamental Plants: Research Reports and Extension Summaries, 1998. pp. 94-104.
|Table 1. Apple Scab Ratings for Crabapple Selections at Secrest Arboretum in 2000.|
|Crabapple||Sept 7||Aug 2||July 7||June 14|
|'Adirondack'||0.00 a *||0.00 a||0.00 a||0.00 a|
|'Bob White'||0.00 a **||0.00 a||0.00 a||0.00 a|
|'Camelot'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Callaway'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Canterbury'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Dolgo'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Excalibur'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Firebird'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Foxfire'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Golden Raindrops'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Guinevere'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Hamlet'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Holiday Gold'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Jackii'||0.00 a||0.00 a||0.00 a||0.00 a|
|'King Arthur'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Lollipop'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Louisa'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Prairie Maid'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Purple Prince'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Rawhide'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Silver Moon'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Sinai Fire'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Strawberry Parfait'||0.00 a||0.00 a||0.00 a||0.00 a|
|'Tina'||0.00 a||0.00 a||0.00 a||0.00 a|
|Malus sargentii||0.00 a||0.00 a||0.00 a||0.00 a|
|'Brandywine'||0.25 a||0.25 ab||1.00 c||0.00 a|
|'Prairifire'||0.80 b||0.60 bc||0.40 ab||0.00 a|
|'Cinderella'||1.00 bc||0.00 a||0.00 a||0.00 a|
|'Candymint'||1.00 bc||0.40 ab||0.00 a||0.00 a|
|'Coralburst'||1.00 bc||1.00 cd||1.00 c||0.00 a|
|'David'||1.00 bc||0.00 a||0.00 a||0.00 a|
|'Lancelot'||1.00 bc||1.00 cd||1.00 c||0.00 a|
|'Pink Princess'||1.00 bc||0.40 ab||0.00 a||0.00 a|
|'Red Jewel'||1.00 bc||1.00 cd||0.80 bc||0.20 a|
|'Manbeck Weeper'||1.20 cd||1.00 cd||1.00 c||1.00 c|
|M. floribunda||1.40 de||1.40 def||1.60 de||1.00 c|
|'Professor Sprenger'||1.40 de||1.00 cd||1.00 c||0.60 b|
|'Mary Potter'||1.60 ef||1.20 de||1.20 cd||1.00 c|
|'Sugar Tyme'||1.80 fg||1.20 de||1.20 cd||1.00 c|
|'Donald Wyman'||2.00 g||1.00 cd||1.00 c||0.00 a|
|'Doubloons'||2.00 g||1.20 de||1.00 c||1.00 c|
|'Molten Lava'||2.40 h||1.40 def||1.00 c||1.00 c|
|'American Salute'||2.60 hi||2.20 hi||2.40 fg||1.80 fg|
|'Canary'||2.75 hij||1.75 fg||2.00 ef||1.75 efg|
|'Sentinel'||2.80 ij||1.60 efg||1.60 de||1.60 ef|
|'Adams'||3.00 jk||2.60 ij||1.80 e||1.60 ef|
|'Red Splendor'||3.00 jk||2.00 gh||2.00 ef||1.80 fg|
|'Royal Fountain'||3.00 jk||2.00 gh||1.80 e||1.40 de|
|'Silver Drift'||3.00 jk||2.00 gh||2.00 ef||2.00 g|
|'Snowdrift'||3.00 jk||2.00 gh||1.80 e||1.60 de|
|'American Spirit'||3.20 k||3.00 jk||3.00 hi||2.00 g|
|'Royal Scepter'||3.75 l||2.75 j||1.75 e||1.50 def|
|'Red Jade'||3.80 l||3.00 jk||2.00 ef||1.20 cd|
|'American Masterpiece'||4.40 m||3.00 jk||3.00 hi||3.00|
|'Harvest Gold'||4.40 m||3.40 kl||3.40 ij||3.00 j|
|'Jewel Berry'||4.40 m||2.80 j||3.00 hi||2.40 h|
|'White Cascade'||4.60 mn||3.40 kl||3.20 hij||2.80 ij|
|'Pink Satin'||4.80 no||3.80 l||3.00 hi||3.00 j|
|'Spring Snow'||4.80 no||3.60 l||2.80 gh||2.80 ij|
|'Weeping Candied Apple'||4.80 no||3.80 l||3.20 hij||3.00 j|
|'American Triumph'||5.00 o||3.00 jk||3.00 hi||2.00 g|
|'Indian Magic'||5.00 o||3.75 l||3.00 hi||2.50 hi|
|'Thunderchild'||5.00 o||5.00 m||3.60 j||3.00 j|
* 0 = no scab observed; |
1 = less than 5% of leaves affected and no aesthetic impact;
2 = 5-20% of leaves affected, with some yellowing but little or no defoliation, moderate aesthetic impact;
3 = 20-50% of leaves affected, significant defoliation and/or leaf yellowing, substantial aesthetic impact;
4 = 50-80% of leaves affected, severe foliar discoloration and defoliation, severe aesthetic impact; and
5 = 80-100% of foliage affected, with 90-100% defoliation.