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James A. Chatfield, Ohio State University Extension, Northeast District/Horticulture and Crop Science; Erik A. Draper, Daniel A. Herms, Kenneth D. Cochran, |
Apple scab pressure was high at the Secrest Arboretum of the Ohio Agricultural Research and Development Center (OARDC) of the Ohio State University 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 1 on page 95).
Sixty three crabapple taxa were planted in 1997-1998 at the Secrest Arboretum of OARDC (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 13, July 9, August 2, and September 19, 2001, 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.