Trunk of an elm tree stricken by Dutch elm disease, showing tracks of a bark-boring beetle, a vector of the fungus, Ophiostoma ulmi, which is the causative agent of Dutch elm disease. The sticky conidia of the fungus adhere to the fertilised female beetles & are deposited under the bark where they germinate. Infection spreads rapidly, but is confined to the water conducting vessels of the tree. The symptoms of the disease are yellowing & browning of foliage followed by wilting, defoliatin & finally death.