176 Gerhold: Crabapple Cultivars As Street Trees Arboriculture & Urban Forestry 2007. 33(3):176–181. Crabapple Cultivars Tested As Street Trees: Third Report Henry D. Gerhold Abstract. Through the Municipal Tree Restoration Program, cooperators planted 22 crabapple (Malus) cultivars in 31 communities for evaluation as street trees, typically comparing two in each community. Standardized measurements in years 1, 2, 3, 6, 9, and 12 revealed differences in height, crown width, and foliage health. These are useful for selecting the most appropriate cultivars for various site conditions. Only the tallest cultivars, ‘Spring Snow’ and ‘Red Barron’, have reached an average height of 6.5 to 6.7 m (21.5 to 22 ft) in 12 years, which is still below most electric distribution lines. Yearly growth patterns varied somewhat among locations and cultivars. The rate of height growth of most cultivars has been declining during years 9 to 12, and in many cases appears to be leveling off at heights between 4 and 6 m (13.2 and 19.8 ft). Red Jewel, Sugar Tyme, and Centurion have narrower crowns, whereas others are still enlarging. Foliage health remained good to excellent throughout the summer on all but seven of the cultivars, and even these retained more than half of their leaves in good condition. Key Words. Crabapple cultivars; Malus; performance testing; street tree evaluation. In 1987, the Municipal Tree Restoration Program (MTRP) started evaluating crabapple (Malus) cultivars and other spe- cies as street trees. MTRP encourages municipalities to im- prove their tree programs by demonstration plantings of free trees and through research provides helpful information for selecting species and cultivars that are compatible with utility wires. Previous reports (Gerhold et al. 1994; Gerhold 2000) indicated that most of the 17 crabapple cultivars that had been selected for superior disease resistance and growth habit had healthy foliage and grew well. However, many differences were found in their growth rates, and some problems had been noted. MATERIALS AND METHODS Plants and Experimental Design Cooperators planted the crabapple cultivars during 1987 to 1998 in 30 Pennsylvania, U.S. communities and one in Mary- land. Representatives of the communities chose the planting sites with the advice of utility foresters, service foresters in the Bureau of Forestry, or Penn State extension urban foresters. Each test planting in a community consisted of two culti- vars, except for the one in Maryland, which had three culti- vars, and a single cultivar in a second test in Mansfield, Pennsylvania. Typically, the paired cultivars were planted alternately within 4 to 10 plots that contained 4 to 16 trees each for a total of 48 to 50 trees. All of the trees being tested were planted along streets and under electric conductors. The local utility company arranged for the removal of any large ©2007 International Society of Arboriculture trees that interfered with utility lines, thus making space for planting in some plots. Plant Materials The test trees came from several nurseries as balled-and- burlapped stock, and the same nursery always supplied the two or three cultivars for a community. Calipers ranged from 4.4 to 5.1 cm (1.76 to 2 in) and average heights from 2.2 to 3.8 m (7.3 to 12.5 ft). The wide range in heights presumably could be explained by genetic differences among cultivars and diverse cultural differences among the nurseries that sup- plied the trees. Measurements and Analysis A trained cooperator inspected and measured the trees soon after planting, then annually during the first 3 years, and at 3-year intervals afterward. During September or October, a service forester or extension urban forester, using standard- ized procedures, measured tree height, trunk diameter at breast height, and crown width; classified the health of fo- liage, branches, and trunk separately; and rated maintenance needs and overall quality. The health of foliage and branches was estimated according to the percentage injured using a 5-point scale: 1 65 to 100, 2 45 to 60, 3 25 to 40, 4 5 to 20, 5 <5. The scale for trunk injuries was 1 tree dead, 2 severe injuries, 3 moderate, 4 slight, 5 no injuries. Causes of injuries such as diseases, insects, drought, or mechanical damage were identified when pos- sible and recorded.
May 2007
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