An Index of Common Tree Diseases

The disease Phellinus weirii occurs in patches (infection centers) sporadically distributed in clusters throughout its range. The most susceptible hosts are Pacific silver fir, white fir, grand fir, Douglas-fir, and mountain hemlock.

Littleleaf disease is the most serious disease of shortleaf pine in the Southern United States. Affected trees have reduced growth rates and usually die within 6 years. The disease is caused by a complex of factors including the fungus Phytophthora cinnamomi Rands, low soil nitrogen, and poor internal soil drainage. Often, microscopic roundworms called nematodes and species of the fungal genus Pythium are associated with the disease.

Lucidus root and butt rot disease is one of the most common root and butt rots of hardwoods. It has a wide host range including oaks, maples, hackberry, ash, sweetgum, locust, elm, mimosa, and willows, and is found throughout hardwood forests. Host trees normally decline for a variable period of time and then die.

Members of the genus are parasites of conifer and hardwood trees and shrub in the Western Hemisphere. There are seven species of native true mistletoe that are found on hardwoods in many parts of Eastern, Western, and Southern United States. The one most commonly known and widespread is P. serotinum (also known as P. flavescens) which occurs mainly in the East and Southeast.

Oak wilt, Ceratocystis fagacearum, is a disease that affects oaks (especially red oaks, white oaks, and live oaks). It is one of the most serious tree diseases in the eastern United States, killing thousands of oaks each year in forests and landscapes. The fungus takes advantage of wounded trees - the wounds promote infection. The fungus can move from tree to tree through roots or by insects. Once the tree is infected there is no known cure.

Powdery mildew is a common disease that appears as a white powdery substance on the leaf surface. The powdery appearance comes from millions of tiny fungal spores, which are spread in air currents to cause new infections. It attacks all kinds of trees.

Scleroderris canker, caused by the fungus Gremmeniella abietina-Scleroderris lagerbergii (Lagerb.) Morelet, has caused extensive mortality in conifer plantations and forest nurseries in the northeast and north central United States and eastern Canada.

Sooty mold appropriately describes the disease, as it looks just like chimney soot. Although unsightly, it seldom damages the tree. The pathogens are dark fungi growing either on the honeydew excreted by sucking insects or on exuded material coming from leaves of certain trees.

A phenomenon known as Sudden Oak Death was first reported in 1995 in central coastal California. Since then, tens of thousands of tanoaks (Lithocarpus densiflorus), coast live oaks (Quercus agrifolia), and California black oaks (Quercus kelloggii) have been killed by a newly identified fungus, Phytophthora ramorum. On these hosts, the fungus causes a bleeding canker on the stem.

Verticillium wilt is common in many soils and affects several hundred herbaceous and woody plant species. Ash, catalpa, maple, redbud and yellow poplar are most frequently infected trees in the landscape but rarely in natural forest conditions. This disease can become a serious problem on susceptible hosts in infested soils but many tree varieties have been developed with some resistance.

The disease attacks pines with 5 needles per fascicle. That includes Eastern and Western white pine, sugar pine and limber pine. Seedlings are in greatest danger. Cronartium ribicolais a rust fungus and can only be infected by basidiospores produced on Ribes (current and gooseberry) plants. It is native to Asia but was introduced to North America. It has invaded most white pine areas and is still making progress into the Southwest and into southern California.