Gardening in the Sky: Nightmare on Elm Trees

Nothing scares gardeners more than the threat of invasive pathogens and insect pests. Over the last century many of America's most beloved, as well as ecologically and economically important, trees have been seriously impacted by the accidental introduction of foreign organisms. Dutch elm disease, white pine blister rust, and emerald ash borer are just a few of the invasives that have changed the composition of our northeastern forests. Perhaps the most devastating example is Chestnut blight, a pathogenic fungus accidentally introduced in the early 1900s through nursery imports of Japanese and Chinese chestnuts. By the 1940s this fungus had killed over three and a half billion American chestnuts (Castanea dentata), permanently altering the character of our forests. With a range extending between Georgia and Central New England, the American chestnut was a dominant woodland species which provided essential forage for animals like bear, deer, and turkey. In some parts of the Appalachia Mountains, one in every two trees was chestnut.

To prevent this kind of mass-scale devastation, scientists and horticulture practitioners have developed the Sentinel Plant Network, which "leverages public garden professionals, volunteers and visitors in the early detection of high-consequence plant pests and pathogens." This summer, FHL gardeners, Orrin Sheehan and Nathan Bartholomew, attended a Sentinel Plant Network training to learn about current and potential threats to our local trees. They are now training to become First Detectors through the National Plant Diagnostic Network. Working with plants everyday means that gardeners are in a good position to notice signs of pest damage early on. They can then submit diagnostic samples to our local labs to help in the early detection of high consequence plant pests.

Here are a few of the pests horticulturists and home gardeners are keeping an eye out for:

SPOTTED LANTERN FLY (Lycorma delicatula)

The spotted lantern fly is about 1" long and ½" wide. Image : Pennsylvania Department of Agriculture

This East Asian planthopper attacks pine (Pinus), apple (Malus), willow (Salix), and stone fruit (Prunus), among other trees. In fall, the lantern fly lays its eggs on smoot-barked trees, like the tree of heaven (Ailanthus altissima), or on other smooth surfaces like crates, firewood, outdoor furniture and equipment. In southeastern Pennsylvania, where this insect has been identified in several counties, there are restrictions on transport of materials that are likely to harbor eggs. The egg masses have a coating like dried mud and, if found, should be scraped off, double bagged and disposed of.

EMERALD ASH BORER (Agrilus planipennis)

The emerald ash borer is about ½" long by 1/8" long. Image: New York Invasive Species Information

The emerald ash borer (Agrilus planipennis), also from East Asia, is a wood-boring beetle that is now confirmed in 28 states, including New York. Most likely introduced through wooden packing materials, since 2002 this borer has killed hundreds of millions of ash trees (Fraxinus). The larvae bore through the outer bark and feed on living tissue, called cambium, thereby destroying the tree's capacity to transport nutrients. D-shaped exit holes in an ash's bark indicate the presence of the beetle. The USDA is now enforcing firewood quarantines to slow the spread of the emerald ash borer.

OAK SPLENDOR BEETLE (Agrilus biguttatus)

In the same genus as emerald ash borer, the oak splendor beetle species attacks and kills oak (Quercus) and beech (Fagus) trees by destroying their cambium. The oak splendor beetle is native to Europe and Africa and has not been found in the US. Officials worry, however, that it could be transported through shipping materials in the same manner as the emerald ash borer.

Once a pest becomes established, it is very costly and difficult to eradicate. For example, the US Forest Service puts the cost of dealing with the emerald ash borer infestation at about $10.7 billion. Given the havoc some of these pests have wreaked in our area, Sheehan is not entirely kidding when he quips, "Only YOU can prevent total ecosystem collapse." He urges home gardeners to learn about the pests that pose a threat to our local ecosystems and how to limit their spread. The Sentinel Plant Network offers many useful resources and First Detector classes may also be hosted by your local Sentinel Plant Network garden, Extension office or Land Grant university. If we are all vigilant we can protect the trees of our forests, parks, and neighborhoods from suffering the fate of the American chestnut.

Our horticultural team counts on members and friends like you to help keep the High Line beautiful and thriving. Join our community of supporters who play an essential role in the High Line's most important gardening projects.

TD Bank is the Presenting Green Sponsor of the High Line.

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