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How did Dutch elm disease damage elm trees in the United States and Europe?

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Two Amanita pantherina mushrooms with brown caps covered in white spots grow among moss and fallen leaves. — fungus A pair of panther cap mushrooms (*Amanita pantherina*). Closely related to the death cap mushroom (*Amanita phalloides*), the panther cap is highly poisonous.

Dutch elm disease is a devastating condition caused by ascomycete fungi in the genus Ophiostoma that has decimated elm populations across Europe and North America.1

The fungus is primarily spread by bark beetles, which carry fungal spores on their bodies. When these beetles feed on the twigs of healthy trees, the spores enter the xylem—the tree's water-conducting vessels—where they reproduce rapidly. The infection can also spread between trees through natural root grafts.1

Once infected, a tree’s leaves typically wilt, turn yellow or brown, and drop prematurely. The disease causes a characteristic brown or black discoloration in the sapwood. While young, rapidly growing trees may die within months, older trees may succumb over several years. Control efforts focus on managing beetle populations by removing dead or dying wood and using insecticides, as current fungicide treatments are generally more protective than curative.1