Which of the following diseases affects hardwood trees?

Both Chestnut Blight and Oak Wilt are diseases that specifically affect hardwood trees. Chestnut Blight, caused by the fungus Cryphonectaria parasitica, primarily targets American chestnut trees, leading to significant declines in their populations. This disease is particularly notable because it played a major role in the near extinction of the American chestnut in Eastern forests.

Oak Wilt, on the other hand, is caused by the fungus Bretziella fagacearum and affects a variety of oak species. It disrupts the tree's water transport system, ultimately leading to wilt and death, especially in red oaks, which are highly susceptible.

Both diseases have serious implications for hardwood ecosystems, influencing biodiversity, forest composition, and associated wildlife habitats. The other options provided, while significant in their own contexts, do not affect hardwood trees in the same manner as Chestnut Blight and Oak Wilt do.