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James A. Chatfield and Erik.A. Draper
Associate Professor, Ohio State University Extension
Assistant Professor, Ohio State University Extension
A paper from the Proceedings of the 12th Metropolitan Tree Improvement Alliance Conference (METRIA 12), Landscape Plant Symposium: Plant Development And Utilization, held in Asheville, NC, May 23-25, 2002, co-sponsored by the North Carolina State University, North Carolina Division of Forest Resources, USDA Forest Service Southern Region, North Carolina Landscape Association, North Carolina Association of Nurserymen, The Landscape Plant Development Center, The North American Branch of The Maple Society, and The International Ornamental Crabapple Society.
The International Ornamental Crabapple Society (IOCS) was established in 1986 to evaluate ornamental crabapples (Malus taxa) for apple scab and other diseases and ornamental aesthetics as well as to promote crabapples for diverse environmental and landscape design situations. As part of the IOCS program a National Crabapple Evaluation Program was set up throughout the United States, with 17 replicated trial plots currently part of the program. This article details some of the key findings in the past decade at one of those plots, namely the Crablandia plots at the Secrest Arboretum at the Ohio Agricultural Research and Development Center of the Ohio State University in Wooster, Ohio
At Secrest Arboretum the Crablandia I plot consisted of 46 crabapple taxa with three single plant replicates planted in a completely randomized design. Crablandi I was established in 1983. The Crablandia II plot currently consists of 63 crabapple taxa with five single plant relpicates planted in a completely randomized design. Crablandia II was established in 1998. Three examples of data collected from these plots are presented and discussed below.
In both Crablandia I and Crablandia II, crabapples were evaluated monthly for aesthetic characteristics, from September 1992 through 2000 in Crablandia I and from 2000-2002 in Crablandia II. Detailed results of these aesthetic ratings are presented elsewhere (1-2), but from these monthly ratings full seasonal profiles have been developed for crabapple taxa in the plots, providing information on the full range of ornamental characteristics of crabapples, from flower and fruit to foliage and form. Following are a short list of fifteen diverse crabapple taxa with examples of short profiles developed from these aesthetic ratings. This is not a Top 15 list as such lists are too limiting, but rather these 15 examples reflect the diversity of crabapple taxa and the range of characteristics considered in the profiles.
|Crabapple||Time of Effective Fruit Display1||Mature Tree Size||Description||Comments|
|'Adirondack'||Late August to mid-December||12-15 feet||Orange-red fruits, white flowers, narrow upright form.||
Positives: One of the best crabapples for tight,
columnar form; great autumn fruit/foliage combination;
fruit ripens to a deep orange-red; fruit appears
singular rather than clustered; annual consistent
flowers are red-tinged.
|Malus baccata 'Jackii'||Mid-August to late January||18-20 feet||Maroon-red fruits, white flowers, broadly rounded form.||Positives: Reliable flower display; large-glossy
green leaves, by far the best foliage of any
crabapple in the plot; outstanding fall contrast
of yellow to rust colored leaves against attractive
maroon-red fruit; bark has an orange cast.
Negatives: Relative sparsseness of fruit clusters and mediocre overall winter appearance.
Diseases: No scab.
|'Bob White'||Mid-October to late January||18-20 feet||Gold-yellow fruits, white flowers, broadly rounded form.||Positives: Persistent, small, firm fruits maturing
mid-winter into striking orange-gold color; an
excellent fruit color for fall and winter landscape;
exceptional floral display of delicate white
blossoms mixed with pinkish-red buds; overall
one of the better yellow-fruiting selections
of the plot.
Negatives: Fruit/floral display alternates yearly from profuse to sparse; lacks summer appeal due to inconspicuous green fruit color.
Diseases: No scab.
|'Canary'||Mid-August to mid-November||12-15 feet||Yellow fruits, white flowers, upright open form.||Positives: Bright yellow, tiny fruits hand
in clusters along branches to accentuate open
form; good autumnal fruit/foliage combination
creates a blaze of yellow; cider brown fruit
generates aesthetic interest in a fall with mild
Negatives: Some early defoliation from scab in wet springs; fruit deteriorates rapidly to cider brown and falls off quickly after a few frosts.
Diseases: Minor leaf and trace of fruit scab.
|'Candymint'||Mid-July to late November||8-10 feet||Red-purple fruits, pink flowers, low spreading form. M. sargentii selection.||Positives: Graceful low spreading form; reliable
fruit/floewr displays; burgundy-tinged leaves;
new stems area deep burgundy; new foliage is
striking, shiny wine-red.
Negatives: slow growing; fruit display is never overwhelming; dull summer leaf appearance.
Diseases: Trace of leaf scab.
|'Excalibur'||Mid-July to mid-December||8-10 feet||Golden-yellow fruit, white flowers, dwarf rounded form.||Positives: Consistent rounded tree form; tiny,
small, shiny fruit is outstanding in the fall;
fruit-lined branches create a striking specimen
in the landscape; fruits mature to a shiny cider
brown color but interest still retained.
Negatives: Flowers can be hidden by rapidly expanding foliage; fruit is hidden to the plant interior until leaves drop.
Diseases: No scab; apple mosaic virus noted.
|'Holiday Gold'||Late September to late March||15-18 feet||Golden-yellow fruits, white flowers, open spreading form.||Positives: one of the best new, yellow-fruited
crabapples in the plot; annual flower show and
fruit display is excellent; attractive cream-yellow
frits mellow to golden yellow; rose blush accents
yellow fruits; fruits hang in distinct clusters
Negatives: Tree form may become awkward due to fruit load.
Diseases: No scab; trace of fireblight.
|'Louisa'||Late July to mid-November||12-15 feet||Lemon-gold fruits, pink flowers, true weeper form.||Positives: Reliable annual bloom is a true
pink; flower display is extraordinary, with pink
cloud-like arrays; arching, graceful branches
are upswept at ends; tree form is greatest asset;
fruit mellows to a gold-orange with rose blush
Negatives: Fruit set is consistently light and scattered, never dazzling.
Diseases: No scab.
|'Manbeck's Weeper'||Mid-September to mid-January||6-8 feet||Cherry-red fruits, white flowers, spreading weeper form.||Positives: Exquisite mix of pink buds opening
to white blossoms; reliable annual fruit and
flower displays; shiny red fruit accents the
elegant, spreading weeper growth habit; new twig
growth is an attractive red color.
Negatives: Pruning necessary to keep center from becoming too cluttered.
Diseases: Trace of scab.
|'Molton Lava'||Early September to mid-December||12-15 feet||Red-orange fruits, white flowers, mounded spreading form.||Positives: Consistent, profuse flower/fruit
shows; fiery red fruits and yellowing fall foliage
on cascading branch structure create a "molten
lava" effect; excellent winter ratings dur to
layered horizontal branching; feathery effect
created by red pedicels after fruit drops;
Negatives: branches somewhat cluttered as tree matures; lacks summer appeal.
Diseases: Minor scab.
|'Prairifire'||Lae June to early December||15-18 feet||Red-purple fruits, coral-pink flowers, open rounded form.||Positives: Yearly spectacular bloom and fruit
displays; blooms contrast with newly emerged
red-tinted green foliage; firm purplish fruits
slowly age to cherry-red; outstanding fall foliage
colors range the spectrum from red to orange
to apricot; attractive lenticel-speckled bark.
Negatives: Mediocre winter and early summer appearance.
Diseases: Trace of scab.
|M. sargentii||Mid-August to late October||6-8 feet||Dark red fruits, white flowers, low spreading form.||
Positives: greatest asset is attractive, low-spreading
growth habig; petite snoy-white blossoms; effective
firm fruits in late summer to early fall.
|'Strawberry Parfait'||Mid-August to mid-April||15-18 feet||Red-cream fruits, pink flowers, open spreading form.||Positives: Fruits age to deep red; yerly pink
flowers borne on spur-lined branches; newly emerged
foliage is a burgundy color; leaves mature to
green with burgundy tint; unusual somewhat erratic
upright-spreading growth habit; good fall color;
fruits remain firm through late winter.
Negatives: Tenacious fruit mummies; unusual shape is not for every landscape.
Diseases: Trace of scab.
|'Sugar Tyme'||Late September to early April||15-18 feet||Cherry-red fruits, white flowers, mounded spreading form.||Positives: stunning sugar-white floral display
from pale pink buds; showy, persistent firm fruiits
through late wnter; good overall form; dense
Negatives: Mediocre appearance during summer before fruit colors; foliage appears off-color or chlorotic during mid to late summer; previous season's fruit drops all at once before bloom.
Diseases: Minor scab.
1Time of Effective Fruit Display derived from observations conductly monthly throughout the year. Effective fruit impact is defined as the period from the tree's fruit first contributes to tree aesthetics until the fruit is no longer ornamental.
Apple scab (pathogen: Venturia inaequalis) is recognized by everyone as a key disease problem of ornamental crabapples, on some taxa resulting in significant foliage and fruit symptoms. Following is an example of one year of apple scab evaluations at Secrest Arboretum. Apple scab pressure was high at the Secrest Arboretum in 2001. Yet, even under this considerable disease pressure, 20 of the 63 taxa showed no evidence of apple scab in 2001 and a total of 30 never received a rating that exceeded 1 (no aesthetic impact) on any evaluation date. Twenty-one taxa received a rating of 3 or higher on at least one date in 2001, indicating substantial defoliation and aesthetic impact (Table 2).
Sixty three crabapple taxa were planted in 1997-1998 in Crablandia II at the Secrest Arboretum 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 13 June, 9 July, 2 August, and 19 September 2001, 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.
Apple scab ratings of crabapples at Secrest Arboretum for the 2001 season are presented in Table 2. Some key findings in 2001 included:
|Crabapple Taxon||Sept. 19||August 2||July 9||June 13|
|'Weeping Candied Apple'||4.80q||4.00j||3.75m||3.00g|
*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.
5 = 80-100% of foliage affected, with 90-100% defoliation.
**Means with the same letter in a column are not significantly different (LSD test, p<0.05).
One of the questions that is often asked of plant pathologists is to predict how bad a disease will be in an upcoming season. Plant pathologists usually hedge a great deal, though sometimes predictions are made based on how bad the disease was in a previous season, with inferences made relative to the future based, for example, on the probable amount of overwintering inoculum available for infection the next year. Relative to this and relative to apple scab in particular, the following graph illustrates the dangers of making such predictions. Table 3 indicates the amount of apple scab disease (based on the 0-5 scale described above) on the 46 crabapple taxa in Crablandia I from 1993-2000. The numbers are based on the August scab ratings in the plots, averaged over all of the taxa. Of particular note, see the years 1999 and 2000. In 1999 the relatively dry spring and summer weather in Wooster, Ohio resulted in the second lowest average scab in the plot over the 8 year period of the study. In 2000, the unusually wet spring and early summer weather in Wooster, Ohio resulted in the highest average scab in the plot in the 8 years of the study. To try to predict in the winter of 2000 how much scab would occur in the upcoming growing season, based on the low level of scab in 1999 would have been futile, since the then unknown upcoming environmental conditions in 2000 were the trump card.
Table 3. Apple Scab on Crabapples at Secrest Arboretum: 1993-2000
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Format updated August 3, 2009