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Currently, there is only one parsley hawthorn (Crataegus marshallii) in the arboretum collection. It grows on a steep slope, in full sun, near the southwest corner of Mickle Hall. Overall, this parsley hawthorn is a very fine specimen whose growth has been unhindered. This has allowed the tree to develop a nice form and it positively exudes an aura of health.
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Unfortunately, despite this vigor, our parsley hawthorn is battling a fungal infection. Over the past several weeks, the rounded canopy has exhibited a pink hue, not from any ripening fruit, but from a pervasive 'rust:' a fungus. In the above photo, we can see remnants of hawthorn fruits mottled by fungal strands.
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The parsley hawthorn leaves show minor damage, but this year the fruits are a total loss.
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The orange strings are tubes that release fungal spores into the environment. These spores need to land on an evergreen host to continue their life cycle.
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The parsley hawthorn lost a reproductive season, and the fungal infection is unsightly, but the overall health of this hawthorn isn't brought into question. However, multiple seasons of such abuse might very well undermine its longevity. Furthermore, this hawthorn isn't the only victim. Hawthorns, mayhaws and our lone crab apple tree have all suffered from this rust, or one of the several different rusts that are carried by the eastern red cedar (Juniperus virginiana). You can read about the ongoing battle on older blog posts, found here, here and here. In 2021, one healthy eastern red cedar, which was thoroughly colonized by one or multiple rusts, was removed from the catalogue. This past spring we identified another eastern red cedar, whose twigs are serving as hosts for these fungi; it might also be removed, in the hopes of protecting the diverse collection of hawthorns.
