Hickory trees produce edible hickory nuts and also provide decoration and shade in the home landscape. The trees grow up to 50 feet tall and survive in USDA Hardiness Zones 4 through 8. Hickory trees can catch diseases, which gardeners have more success preventing than treating post infection.
Anthracnose fungus attacks hickory trees, causing spots on their leaves. The spots have irregular shapes and purplish coloring on the top of the leaves with brown coloring underneath. Anthracnose can cause defoliation, which reduces photosynthesis and the overall vigor of the tree. Like other fungal diseases, anthracnose likes wet conditions. Therefore, hickory growers should prevent the disease by spacing the trees out enough to allow their leaves to get ventilation after heavy rains.
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Several different types of fungi cause similar leaf spots in hickory trees and other leafy shade trees. The University of Illinois Extension lists cercospora, coniothyrium, cristulariella, sphaceloma, elsinoe, gnomonia, hendersonia, marssonina, microstrom, monochaetia, mycosphaerella, phyllosticta and septoria as fungi that cause leaf spot disease on hickory trees. These fungi cause white, gray, tan, red, brown or purple spots on hickory tree leaves. The spots generally start off small and grow larger with time. They sometimes have a lighter gray or tan color on the inside and a black or dark brown ring around the outside. Minor infections usually do not require treatment. However, gardeners may want to spray trees with a fungicide or horticultural oil to control severe infections that may cause leaf drop. Growers can also prevent the fungi from occurring in the first place by planting hickory trees with plenty of space between them for good ventilation.
Hickory trees are susceptible to fungi that cause their trunks to rot. The U.S. Department of Agriculture Forest Service warns that hickory trees with fire or logging damage sometimes start to rot. Trunk rot may not be treatable and can kill trees or make them a falling hazard. Proper protection from damage helps keep trees healthy and resistant to trunk rot fungi.
Fungi sometimes start to rot the roots of trees with poor soil drainage or excessive irrigation. Growers should avoid planting hickory trees in compacted soil, although unavoidable unusually wet weather also causes root rot. Root rot causes a decline in growth and foliage health. It can eventually kill hickory trees.
The U.S. Department of Agriculture Forest Service considers canker rot the most serious hickory tree disease. A fungus causes cankers to form around dead branches. The fungus looks unattractive and can eventually spread throughout the tree wood and kill off the hickory. Gardeners should prevent canker rot with sterile pruning techniques.
- National Gardening Association: I'm Nuts over Nuts
- Washington Post: Fungal Disease Dooms Hickory
- U.S. Department of Agriculture Forest Service: Shagbark Hickory
- University of Illinois Extension: Fungal Leaf Spot Diseases of Shade and Ornamental Trees in the Midwest
- Virginia Cooperative Extension: Anthracnose - A Fungal Disease of Shade Trees