MELeaf: A Newsletter From the Horticulture Program, August 31, 2021
In this issue:
Some plants are easier to identify late in the summer and into the fall. The Horticulture Program is interested in finding populations of the invasive plants below, that have characteristics that make them easier to identify this time of year.
Tree of Heaven
Tree of heaven (Ailanthus altissima) is a non-native tree from China that was introduced to the U.S. in the late 1700s as an ornamental. Because of its hardiness and ability to grow in harsh environments, it was widely planted as a street tree. Today, it is considered one of the most noxious plants due to its severe invasiveness and its foul odor.
In addition, this tree inhibits the growth of beneficial native plants, reducing food sources for native insects which leads to less food for baby birds. And tree of heaven is the preferred host to the destructive spotted lanternfly (Lycorma delicatula), an invasive insect wreaking havoc on grapes, hops, maples, and apples in several mid-Atlantic states.
Little is known about the distribution of tree of heaven in Maine (biologists know of a handful of locations in southern Maine), so we welcome reports of sightings of this tree. By learning to identify and report tree of heaven, you can help biologists keep spotted lanternfly out of Maine and keep tree of heaven from taking over valuable habitats.
Please become familiar with this tree; it looks a lot like sumac (Rhus spp.), with important differences as indicated in the photos below. A key characteristic to look for this time of year: tree of heaven produces seed late in the summer and the seed can persist on plants throughout the winter, look for plants with clusters of 1 to 2 inch long samaras (winged seeds similar to maple seeds).
Please report any sightings of tree of heaven to invasives.mnap@maine.gov
 In the late summer and fall look for trees with clusters of winged seeds.
Japanese stiltgrass
Japanese stiltgrass (Microstegium vimineum) is known to hitchhike on plant material and last year an infestation was found at a nursery in York County. To date there are only two known locations in Maine with populations of Japanese stiltgrass and the Maine Natural Areas Program has been actively working with the property owners on eradication efforts. Japanese stiltgrass is a shallow rooted annual and control methods include hand pulling, mowing and herbicides.
Stiltgrass forms dense colonies in sun or shade, invading the forest and forming a thick thatch layer. The thatch layer makes it difficult for native trees, shrubs, and wildflower seeds to establish and grow. Thatch buildup also raises fire risk. Stiltgrass is an annual plant, and each stem can produce hundreds to thousands of seeds before dying in the fall. Seeds survive for at least five years in the soil.
Japanese stiltgrass can be difficult to distinguish from other grasses, however, they flower and set seed late in the summer and into the fall – much later than many other grasses. Features to look for include:
- Leaves that alternate along the stem, 2-4" long and ½" wide, and have a stripe of reflective hairs along the leaf midrib on the leaf's top surface. The midrib may be slightly off-center.
- The leaf edges and surfaces feel smooth to the touch, unlike some native grasses with stiff hairs along the leaf edge.
- The common name "stiltgrass" comes from the plant's growth habit: it trails along the ground, branching from nodes where it produces "stilts" (roots) to support the new branches. It is shallow-rooted and easy to pull out.
- Plants flower and set seed very late in the season (September-October). Each plant can have one to three seed spikes that resemble crabgrass.
- Stems can develop a reddish tint late in the season.
If you suspect you have Japanese stiltgrass in or around your nursery please contact horticulture@maine.gov. Suspect plants in other locations (forests, roadsides, home or commercial landscapes etc.) should be reported to invasive.mnap@maine.gov.
 Japanese stiltgrass flowers and sets seed late in the growing season. Look for plants with alternating leaves with a pale midrib.
During a recent nursery inspection, an unusual number of fruit trees were found infected with fire blight (Erwinia amylovora). University of Maine Cooperative Extension (UMCE) apple specialists confirmed that fire blight has been particularly severe and widespread in Maine this year.
Fire blight is a native bacterial disease that primarily infects apple, crabapple, and pear trees, and occasionally other plants in the rose family. Bacteria enter plants through natural openings in flowers, as well as wounds on the plant created by mechanical, environmental, or insect damage. The bacteria overwinter within cankers and start multiplying in the spring when temperatures rise. In warm and moist conditions, cankers may ooze bacteria in amber colored sap. Bees and other pollinators, machinery, people, tools and rain can transfer the bacteria between host plants. Internal translocation can also spread blight from infected above-ground water sprouts down to roots.
- Blossoms appear water-soaked, then wilt, turn dark brown and remain attached to the tree.
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Leaves wilt, darken to a fire-scorched color and remain attached to the tree.
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Stems darken and bend forming a shepherd’s crook.
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Cankers on stems appear sunken and dark colored, with a narrow callus ridge that may create open cracks in the bark.
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Infected inner bark changes color from green to brown.
While management of fire blight is built into pest prevention practices at orchards, nurseries selling host plants may be underprepared when optimal environmental conditions cause a flare up of infections. Retail nurseries and garden centers that buy in host trees to be sold the same year may not have issues with this disease if the supplying nursery treated the plants before shipping. However, nurseries that overwinter field grown, potted or B&B hosts may be more at risk and should be prepared for this potentially serious disease. There is no cure for fire blight, so prevention is key!
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Grow/sell resistant varieties.
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UMCE specialists advise nurseries to remove flowers before they open. Understandably this may not be the most appealing management option as flowers and fruit are major selling features for plants.
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Manage insect pest populations to prevent damage to plants where bacteria could enter.
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Prune out cankers and infected stems on dry days by cutting at least 8” below the visible infection and bag and remove cuttings from property.
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Always use clean sanitized tools when pruning or working with host plants.
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Use preventative bactericides during high risk periods as determined by disease forecasting models.
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Avoid excessive irrigation and fertilization of trees exposed to fire blight as infection accelerates on rapidly growing tissues.
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Keep water sprouts and suckers pruned.
 Left: Girdling branch canker due to fire blight, Richard Stuckey, www.bugwood.org. Right: Fire blight infected branch, Penn State University, Department of Plant Pathology & Environmental Microbiology Archives, www.bugwood.org.
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