Spotted lanternfly

Damage symptoms

Spotted lanternflies suck phloem sap. On most garden trees the harm is mainly cosmetic and a nuisance: stress, some branch dieback on favoured hosts such as maples and black walnut, and a great deal of honeydew. Penn State has recorded it killing only grapevines, tree-of-heaven and black walnut saplings. On grapes, repeated heavy feeding depletes the starch stored in the roots, and Cornell reports weakened vines, loss of winter hardiness, reduced crop the following year and vine death. The fermenting honeydew also draws bees and wasps, which raises the risk of stings around infested trees.

• Honeydew falling from the canopy like a light rain, leaving surfaces sticky
• Black sooty mould on leaves, plants, decks, cars and furniture beneath infested trees
• Crowds of nymphs or adults on trunks and branches, especially tree-of-heaven
• Weeping, oozing wounds on bark where they feed
• Wilting, branch dieback and, on grapevines, poor crop or vine death after heavy years
• Bees and wasps attracted to the fermenting honeydew
• Grey-brown mud-like egg masses on bark, stone, fences and vehicles in autumn and winter

Lifecycle & degree days

One generation a year. The winter is spent as eggs, laid from September until the first killing freeze. Nymphs hatch from late April to June; adults appear from July and stay active until a hard frost. Adults move into vineyards from August, and Penn State says the high numbers usually arrive from mid to late September — later, as late as October, in newly infested areas. We found no degree-day model for garden use in the extension sources checked.

Host crops

Penn State has recorded it feeding on more than 70 plant species and Cornell puts it at more than 100, but a few matter most. Tree-of-heaven (Ailanthus altissima), itself an invasive, is the preferred host. Grapes are the main crop at risk: Cornell reports up to 400 adults per vine, and a 2025 study estimated that New York grape growers could lose $1.5 million, $4 million and $8.8 million in the first three years of infestation. Red and silver maple, willows, black walnut saplings, hops and many ornamentals are also fed on. Conifers are not good hosts. Tree-of-heaven is easily confused with native staghorn sumac, so check before you cut.

Monitoring & action thresholds

From autumn to spring, look for egg masses on tree trunks, stones, fences, outdoor furniture and under vehicles and in wheel wells — the stage you can destroy before it hatches. From May, look for black-and-white nymphs on plants; from July, look for adults and honeydew on tree-of-heaven, maples, walnuts and grapes. Vineyards should check vines and the wood edge at least weekly from August to November. Before leaving a quarantine area, check your car, trailer and anything stored outdoors for all life stages. If you find spotted lanternfly somewhere it has not been reported, report it to your state department of agriculture.