Nut trees, such as walnut, pecan, cashew and pistachio, are prevalent throughout the world, including North America, and are valued not only for their edible nuts, but for their timber and the shade they provide. Nut trees, like many other trees, are susceptible to damage from invasive pests and pathogens that can wreak havoc on both established and young trees.
Leaves and Branches
Many nut tree diseases manifest on leaves and branches, according to "The Garden Trees Handbook" by Alan Toogood. Fungus and bacteria cause cankers to form on branches and shoots, such as chestnut blight that shows up on branches; pecan scab, in which black spots form on leaves; hypoxylon canker, which attacks stressed trees like those affected by drought; walnut blight, which attacks not only the leaves, but the nuts, bark and shoots of a walnut tree, manifesting in dark spots; leaf spot, which manifests as small white spots on chestnut trees and powdery mildew, a fungal disease that shows as a white powder on leaves.
Bark and Trunk
Diseases of the bark and trunk of nut trees include chestnut blight, where the bark miner insect burrows into the bark of a chestnut tree, causing cankers to form on the bark; bunch disease, which affects black walnuts, pecans and hickories, according to the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois at Urbana-Champaign.
Many nut tree diseases attack at the root, according to "Gardener's A-Z Guide to Growing Organic Food," by Tanya Denckla and Stephen Alcorn. These include crown gall, which affects the roots and stems of nut trees; Armillaria root rot, which originates in the roots and first causes leaves to die, then the tree and Phytophthora root and crown rot, which occurs when the soil around the base of the tree is too wet for a prolonged time. One other disease is shoe string root rot, which manifests on the trunk but affects the top branches of a tree and can spread to other trees through the soil.