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Comparison of pine needle rust among New England Aster cultivars, 2003

(note:  the following article appeared in the Biological and Cultural Tests of the Amer. Phytopath. Soc., 2004 online 10:0007)

New England Aster plants, obtained from various sources and established for one year in 5.25-in. Jumbo pots, were transplanted in May 2003 into a field plot of Peru stoney loam in Milton, VT. Asters were planted in three, 2-ft. wide rows with three ft. between plants in the row. Rows were divided into two blocks, for a randomized complete block design with each cultivar in the six replicate blocks. Plants were fertilized with organic 5-3-4 Pro Gro (North Country Organics, Bradford, VT) at the rate of 3 lb/100 sq ft in May after planting. Plants were weeded by hand and with targeted applications of glyphosate as needed. Irrigation was supplied to plant bases, manually as needed, to supplement rainfall during the first two months of establishment. Rust began to appear on leaves in late Aug, with peak symptoms in late Sep at beginning of bloom when data were taken on 22 Sep. Percent of leaves showing rust was determined for each plant, then converted to a rating to determine the cultivar mean. Mean differences as significant by ANOVA were separated by Tukey's procedure.

Cultivars of New England Aster did indeed show significant differences in susceptibility to pine needle rust, as had been initially indicated by single plant observations in years prior in a garden setting. In this first year of establishment, all eleven cultivars fell into one of two groups. Those showing least disease and no significant differences were Crimson Beauty, Fanny’s, Harrington’s Pink, Honeysong Pink, Purple Dome, and Wedding Lace. Most susceptible and not significantly different were Alma Potschke, Barr’s Pink, Hella Lacey, September Ruby, and Treasure. Results from this replicated study agreed with observations on single plants nearby in a garden setting for four of seven cultivars also present there. Differences may be related to age of plants or spacing, as those in the garden were several years old and tightly spaced with other plants. Subsequent years of data from this replicated study will show if differences among cultivars are consistent yearly, and irrespective of plant age.

Cultivar    Color    Pine needle rust severity (index value) *
Alma Potschke    bright pink   3.8 cde**
Barr’s Pink    pink   5.0 e
Crimson Beauty    red   1.2 a
Fanny’s    violet-blue    1.0 a
Harrington’s Pink    pink   2.0 abc
Hella Lacey    violet-blue    4.0 de
Honeysong Pink    pink    1.5 ab
Purple Dome    purple   1.0 a
September Ruby    red   3.7 cde
Treasure light    violet   3.2 bcde
Wedding Lace    white   2.3 abcd

Standard Error of Mean 0.28, Significance, P level <0.001

*Rust was rated on a scale of 0-5, with 1 = 0-20%, 2 = 21-40%, 3 = 41-60%, 4 = 61-80%, and 5 = 81-100% of the leaves showing orange rust pustules on either adaxial or abaxial surfaces.

**Numbers in a column with a letter in common are not significantly different according to Tukey's procedure at P = 0.05.

This study made possible by a grant from the New England Greenhouse conference.

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