Ohio State University Extension Bulletin

Ornamental Plants -- Annual Reports and Research Reviews 1999

Special Circular 173-00

Evaluation of Crabapples for Apple Scab at the Secrest Arboretum in Wooster, Ohio: 1999

James A. Chatfield, Erik A. Draper, Kenneth C. Cochran, Peter W. Bristol, and Charles F. Tubesing

Summary

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 1999. Seventeen of the selections had no scab at any of the three ratings in 1999. Compared to average scab ratings over the past seven years, 40 of the 42 crabapple taxa in the plot had equal or lower scab incidence than normal in 1999, reflecting the drier than normal spring and summer weather in Wooster in 1999. Average scab ratings are reported for the past seven years for 28 of the crabapple taxa in the plot, while data for only the past three years is reported for 14 of the more recently planted taxa. Fifteen crabapples removed from the plot in 1998 due to poor overall aesthetics are also summarized for the reader’s information.

Introduction

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.

Table 1. Apple Scab Ratings for Crabapple Selctions at Secrest Arboretum (6-8-99, 7-12-99, 8-11-99),and the Average Rating for Secrest Arboretum from 1993-1999
Crabapple Secrest 6-8-99 Secrest 7-12-99 Secrest 8-11-99 Secrest 1993-1999
M. baccara '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'
0.0
0.3
0.6
0.8
'Dologo'
0.0
0.0
0.0
0.0
'Donald Wyman'
1.0
1.6
2.3
1.5
M. floribunda
1.0
1.0
1.0
0.7
'Harvest Gold'
1.3
1.6
2.0
2.5
'Indian Magic'
1.3
2.0
2.6
2.6
Indian Summer'
1.0
1.0
2.3
2.1
'Liset'
0.0
0.3
1.3
0.9
'Mary Potter'
0.0
1.0
1.0
0.6
'Molten Lava'
0.6
1.0
1.0
1.2
'Ormiston Roy'
0.0
0.0
0.0
0.2
'Prairifire'
0.0
0.0
0.0
0.0
'Professor Sprenger'
0.0
0.0
0.0
0.7
'Red Jade'
1.0
1.0
1.6
1.3
'Red Jewel'
0.0
0.0
0.0
0.1
'Red Splendor'
1.0
1.0
1.0
1.4
M. sargentii
0.0
0.0
0.0
0.0
'Sentinel'
0.0
0.3
1.3
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'
0.0
0.3
0.6
0.6
'White Angel'
0.0
0.0
0.0
0.0
'White Cascade'
1.0
2.0
2.0
2.1
M. zumi 'Calocarpa'
0.0
1.0
1.0
0.8
0= No scab noted.
1= Slight scab; less than 5% of leaves affected; no negative effect on aesthetics.
2= Moderate scab; 5% to 20% of leaves affected; some yellowing; little or no defoliation; moderate negative effect on aesthetics.
3= Extensive scab; 20% to 50% of leaves affected; significant defoliation and/or leaf yellowing; significant negative effect on aesthetics.
4= Heavy scab; 50% to 80% of leaves affected; severe defoliation and discoloration of leaves; severe negative effect on aesthetics.
5= Extreme scab; 80% to 100% of foliage is affected, and defoliation is complete or nearly cornplete.

Table 2. Apple Scab Ratings for Crabapple Selctions at Secrest Arboretum from 1993-1997. These crabapples were discontinued in the plot in 1998 due to poor overall aesthetic ratings.
Crabapple 6-8-99 7-12-99 8-11-99 97-99 Avg.
'Adirondack'
0.0
0.0
0.0
0.0
'Camelot'
0.0
0.0
0.0
0.0
'Canary'
0.6
0.6
1.0
1.7
'Candymint'
0.0
0.0
0.0
0.0
'Glen Mills'
0.3
1.0
1.0
1.5
'Golden Raindrops'
0.0
0.0
0.0
0.0
'Lancelot'
0.0
0.0
0.0
0.0
'Louisa'
0.0
0.0
0.0
0.0
'Narangansett'
1.0
1.0
1.3
1.3
'Pink Satin'
1.0
1.3
1.3
1.4
'Prairie Maid'
0.0
0.0
0.0
0.0
'Purple Prince'
0.0
0.0
0.0
0.0
'Silver Drift'
0.0
0.0
1.0
0.7
'Sinai Fire'
0.0
0.0
0.0
0.0
0= No scab noted.
1= Slight scab; less than 5% of leaves affected; no negative effect on aesthetics.
2= Moderate scab; 5% to 20% of leaves affected; some yellowing; little or no defoliation; moderate negative effect on aesthetics.
3= Extensive scab; 20% to 50% of leaves affected; significant defoliation and/or leaf yellowing; significant negative effect on aesthetics.
4= Heavy scab; 50% to 80% of leaves affected; severe defoliation and discoloration of leaves; severe negative effect on aesthetics.
5= Extreme scab; 80% to 100% of foliage is affected, and defoliation is complete or nearly cornplete.

Table 3. Apple Scab Ratings for Crabapple Selctions at Secrest Arboretum for Crabapples Rated on 6-8-99, 7-12-99, and 8-11-99, and the Average Rating for Secrest Arboretum from 1997-1999.
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.
1= Slight scab; less than 5% of leaves affected; no negative effect on aesthetics.
2= Moderate scab; 5% to 20% of leaves affected; some yellowing; little or no defoliation; moderate negative effect on aesthetics.
3= Extensive scab; 20% to 50% of leaves affected; significant defoliation and/or leaf yellowing; significant negative effect on aesthetics.
4= Heavy scab; 50% to 80% of leaves affected; severe defoliation and discoloration of leaves; severe negative effect on aesthetics.
5= Extreme scab; 80% to 100% of foliage is affected, and defoliation is complete or nearly cornplete.

Materials and Methods

Forty-one crabapples in the replicated crabapple plot at Secrest Arboretum were rated for apple scab disease on June 8, 1999; July 12, 1999; and August 11, 1999. This plot is in a completely randomized design with three replications of each crabapple selection (except for M. zumi ‘Calocarpa,’ with two surviving replicates, and Malus ‘Red Jewel,’ with one surviving replicate). The plot was planted in 1984 and is not treated with fungicides or insecticides.

Apple scab evaluations were based on the following rating system:

0= No scab noted.
1= Slight scab; less than 5% of leaves affected; no negative effect on aesthetics.
2= Moderate scab; 5% to 20% of leaves affected; some yellowing; little or no defoliation; moderate negative effect on aesthetics.
3= Extensive scab; 20% to 50% of leaves affected; significant defoliation and/or leaf yellowing; significant negative effect on aesthetics.
4= Heavy scab; 50% to 80% of leaves affected; severe defoliation and discoloration of leaves; severe negative effect on aesthetics.
5= Extreme scab; 80% to 100% of foliage is affected, and defoliation is complete or nearly cornplete.

Scab on crabapple fruits was factored into the overall scab ratings.

Literature Cited

  1. Chatfield, J. A. and Draper, E. A. 1995. Evaluation of crabapples for apple scab at the Secrest Arboretum in Wooster, Ohio: 1994. The Ohio State University. Ohio Agricultural Research and Development Center. Special Circular 142. Ornamental Plants: A Summary of Research, 1993-1994. pp. 22-26.

  2. Draper, E. A., Chatfield, J. A., Cochran, K. D., Bristol, P. W., and Tubesing, C. E. 1996. Evaluation of crabapples for diseases at the Secrest Arboretum in Wooster, Ohio: 1995. The Ohio State University. Ohio Agricultural Research and Development Center. Special Circular 147. Ornamental Plants: Annual Reports and Research Summaries. pp. 35-40.

  3. Chatfield, J. A., Draper, E. A., Cochran K. D., Bristol, P. W., and Tubesing, C. F. 1997. Evaluation of crabapples for apple scab at the Secrest Arboretum in Wooster, Ohio: 1997. The Ohio State University. Ohio Agricultural Research and Development Center. Special Circular 154. Ornamental Plants: Annual Reports and Research Reviews. pp. 89-93.

  4. 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. The Ohio State University. Ohio Agricultural Research and Development Center. Special Circular 157. Ornamental Plants: Annual Reports and Research Reviews. pp. 83-94.

  5. 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.

  6. Draper, E. A. and Chatfield, J. A. 1996. Magic of Malus. American Nurseryman. August 15, 1996. 184 (4) pp.

  7. Chatfield, J. A., Draper, E. A., Cochran, K. D., Bristol, P. W., and Allen, D. E. 1999. Comprehensive aesthetic evaluations of crabapples at Secrest Arboretum in Wooster: 1993-1998. The Ohio State University. Ohio Agricultural Research and Development Center. Special Circular 165. Ornamental Plants: Annual Reports and Research Reviews, 1998. pp. 94-104.

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