Crabapple Cultivars Tested as Street Trees: Second Report

Methods

Twenty-six communities in Pennsylvania and 1 in Maryland planted the trees represented in this report. Three of the communities had 2 tests planted in different years. Community representatives chose the planting sites with assistance by utility foresters, service foresters, and Extension urban foresters; 2 of these usually assisted each community.

Each test planting consisted of 2 cultivars, except in Dundalk, Maryland, where there were 3, and the second test in Mansfield where there was 1. A typical test consisted of 2 cultivars planted alternately within 4 to 10 plots that could contain 4 to 16 trees each—a total of 50 trees. All test trees were planted along streets and under electric conductors; the utility company arranged for removal of large trees that interfered with utility lines. Both cultivars for a community were ordered B&B from the same nursery, with a caliper of 4.4 or 5.1 cm (1.75 or 2 in.); heights ranged from 2.4 to 3.7 m (8 to 12 ft).

The cultivar tests were planted between 1987 and 1996. A trained cooperator inspected and measured the trees annually during the first 3 years, and then at 3-year intervals. During September or October, a service forester or Extension urban forester used standardized methods to measure tree height, trunk diameter at breast height (dbh), and crown width, and to classify foliage health, branch health, trunk health, maintenance needs, and an overall quality rating (Table 1*). Causes of damage such as disease, insects, drought, and mechanical injuries also were recorded.

An analysis of variance (MINITAB General Linear Model) was conducted on each type of quantitative data from the 2 (or 3) cultivars in a test planting to calculate means and determine significance of differences. Each test location in every year was treated as a separate experiment with plots providing replication. These results, along with written comments of cooperators, were used to characterize performance of the cultivars.

Results

Many of the cultivars paired at each location differed at ages 3, 6, or 9 in height, crown width, and trunk diameter (dbh) (Table 1). Some of these differences already existed when trees were first planted, even though trees of the same caliper were ordered from the same nursery in most cases. Therefore, it is more revealing to compare growth rates than absolute heights (Figure 1, Table 2). Apical growth was slow for the first 2 years, after which the growth rate was essentially linear until at least the ninth year. Brandywine^®, Harvest Gold^®, and ‘Spring Snow’ grew faster than Centurion^®, Madonna^®, Red Jewel^®, and Sugar Tyme^®. More limited data on other cultivars indicate that ‘Red Barron’ grew rapidly, whereas ‘Donald Wyman’, zumi ‘Calocarpa’, and ‘Snowdrift’ grew more slowly in height (Table 2). Data from only the first 3 years proved to be insufficient for classifying growth rates of cultivars, some of which later changed in rank.

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Figure 1.

Average height growth of Brandywine^® (Br), Centurion^® (Ce), Harvest Gold^® (HG), Red Jewel^® (RJ), ‘Spring Snow’ (SS), and Sugar Tyme^® (ST) crabapples.

By the ninth year, the crown widths of Brandywine and Centurion were broader than heights of the same trees. Sugar Tyme was slightly wider than its height, whereas Harvest Gold, Madonna, Red Jewel, and ‘Spring Snow” had narrower crowns (Table 1). The largest trees after 9 years were Brandywine crabs at West Reading, having an average height of 6 m (19.6 ft), a width of 6.9 m (22.6 ft), and dbh of 15.8 m (6.2 in.). The smallest, Sugar Tyme at Ulysses, had an average height of 3.5 m (11.5 ft), a width of 3.6 m (11.8 ft), and dbh of 6.8 cm (2.7 in.).

The foliage of nearly all of the cultivars at all locations was very healthy near the end of the growing season. American Masterpiece^®, American Triumph^™, and Velvet Pillar^™ were the only cultivars that consistently had foliage health ratings below 3.5, indicating more than 25% of their leaf surface area was affected; they had been evaluated at only 1 location. The foliage health ratings of ‘Snowdrift’ averaged 3.8 at 3 locations, equivalent to about 18% of the leaf area injured. Other cultivars that had occasional foliage ratings below 4.0 were American Spirit^™, Brandywine, Harvest Gold, Madonna, and ‘Red Barron’. The main causes of foliage injuries were apple scab, fall webworm, Japanese beetle, and gypsy moths.

The overall quality ratings are somewhat more subjective than the other ratings. Opinions could vary among observers, and 1 observer did change his mind as trees matured (see footnote in Table 1). Most ratings consistently were in the range of 7.0 to 9.0, indicating those cultivars were regarded as very good to excellent in health, appearance, and adaptation to site conditions. The ratings of Brandywine and Madonna were inferior to the other cultivars to which they have been compared. Brandywine has large fruit that can be messy when it drops. Madonna fruit was less attractive due to scab and discoloration, and the cultivar had more basal sprouts than others.

Two kinds of complaints applied to most or all of the crabapple cultivars. Basal sprouting was unsightly and occurred repeatedly. The low branching habit could interfere with pedestrians and vehicles, especially branches of the broader cultivars when planted in confined spaces. Proper pruning could overcome these problems, although many municipalities rely on property owners for maintenance practices.

Conclusions

Cultivars recommended for street trees, based on the evaluations so far, include Centurion, Harvest Gold, Red Jewel, ‘Spring Snow’, and Sugar Tyme. Others that appear promising according to more limited test data include ‘Adams’, ‘Donald Wyman’, ‘Prairifire’, ‘Red Barron’, and zumi ‘Calocarpa’. Differences in size and growth rate should be considered in relation to space limitations when cultivars are selected for planting.