Garden Q&A: Getting rid of tree of heaven, a lanternfly magnet

For The Baltimore Sun

With the spotted lanternfly threatening from Pennsylvania, I don’t want to have one of those trees of heaven that attracts them! I’m terrible at identifying trees. How can I avoid having the neighborhood magnet for these pests?

Tree of heaven itself is an Asian invasive pest, and now we have a huge incentive to eliminate it. Spotted lanternfly flock to it, and it seems necessary to complete their life cycle. However, lanternfly will feed on a wide range of trees, plus crops like grapes. The massive congregations suck juices out of plants and literally rain excrement on anything below (think cars, decks). Attraction of the lanternfly for tree of heaven (Ailanthus altissima) is so strong that a single tree can be used as a trap tree and treated with insecticide to kill multitudes of lanternfly. Most people, however, will want to kill their tree of heaven. Here’s how you can identify them: The leaves, when crushed, have a repugnant odor described as rotten peanut butter. On the very long compound leaves, each leaflet at its base has a small projection with a swollen gland. Bark is smooth (not rough like a walnut or nut trees). The female trees have hanging clusters of flat seed pods (samaras). If you need help identifying a plant, you can always send us a photo.

Never cut down a tree of heaven — it will spring up an army of suckers. Spray foliage with triclopyr or, in summer, use the hack and squirt method on larger tree trunks. Spotted lanternfly is spreading like lightning, since it lays eggs on anything — cars, campers, toys — not just tree trunks. Anyone visiting Pennsylvania should check carefully for egg masses before heading home. Patrol your property and scrape egg masses, mainly on tree trunks, in winter and early spring (look like dried mud patches). Nymph stages are black with white spots, then red and black with white spots. Search “spotted lanternfly” on the HGIC website. Become familiar with adults with wings open or closed. Capture any life stage, put in alcohol, and report to HGIC.

How can I treat my hydrangea to eradicate the black and purple spots on its leaves and flowers?

Once fungal spots appear, you cannot spray anything to remove them. There's really no point in spraying now. The fungal leaf spots may look bad, but they do not do any permanent damage to the hydrangeas. The fungal spores are around every year, but this fungal leaf spot disease is most noticeable under certain weather conditions, such as this year’s. If you have not had problems in the past, your hydrangea will not have problems most years in the future.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Maryland’s Gardening Experts” to send questions and photos.

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