Black locust vs Manna ash

Behaves as an invasive tree. It suckers strongly from both stump and roots: damage to the roots or trunk, hard pruning and felling all trigger masses of suckers, sometimes several metres from the tree, in the lawn, in beds or next door. Its seed stays viable in the soil for decades. It fixes nitrogen and so enriches the soil one-sidedly, leaving a species-poor, weedy ground layer; in Central Europe it irreversibly changes sandy and dry grasslands and woodland edges and is very hard to eradicate. In Hungary it is not on the invasive list of the government decree on the protection of woody plants (the earlier decree did include it, except for horticultural cultivars), and it is not on the EU list either, because of its economic and beekeeping importance. The Hungarian decree on Natura 2000 grasslands, however, names it among invasive and site-alien woody species whose establishment and spread must be prevented there; conservation authorities advise not to plant it where avoidable, and the official Swiss list also treats it as invasive. Ornamental cultivars are usually grafted on the species, so thorny suckers can still come up from the rootstock and roots; the globe form does not flower and therefore sets no seed. Other problems: paired thorns on the branches, brittle branches that break in storms, a globe form that can become top-heavy when grafted on a tall stem, leaves disfigured by leaf-mining insects, occasional powdery mildew and canker, and frequent trunk rot in old trees. It comes into leaf late.

Ash dieback (Hymenoscyphus fraxineus), which is killing common ash across Central Europe, hardly affects manna ash: at most it infects the leaves and does not normally cause shoot dieback. The emerald ash borer (Agrilus planipennis), introduced from Asia, is spreading west from Eastern Europe and is a threat to ashes in general; how badly it attacks manna ash is still uncertain, although some observations suggest it is attacked less. Young shoots can be scorched by late spring frost, and the branches are brittle in storms and under snow.