Science, Tech, Math › Animals & Nature The Deadly Coniferous Tree Diseases Share Flipboard Email Print Getty Images / ollo Animals & Nature Forestry Tree Structure & Physiology Tree Identification Basics Arboriculture The Science Of Growing Trees Conifer Species Individual Hardwood Species Pests, Diseases, and Wildfires Tree Planting and Reforestation Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Dinosaurs Evolution View More By Steve Nix Forestry Expert B.S., Forest Resource Management, University of Georgia Steve Nix is a natural resources consultant and a former forest resources analyst for the state of Alabama. He is a member of the Society of American Foresters. our editorial process Steve Nix Updated March 06, 2017 There are virulent diseases that attack coniferous trees which ultimately cause death or devalue a tree in the urban landscape and rural forest to the point where they need to be cut. Five of the most malignant diseases have been suggested by foresters and landowners at About's Forestry Forum. I have ranked these diseases according to their ability to cause aesthetic and commercial damage. Here they are: #1 - Armillaria Root Disease: The disease attacks both hardwoods and softwoods and can kill shrubs, vines, and forbs in every state in the United States. It is pervasive in North America, commercially destructive and is my pick for the worst disease.The Armillaria sp. can kill trees that are already weakened by competition, other pests, or climatic factors. The fungi also infect healthy trees, either killing them outright or predisposing them to attacks by other fungi or insects.More on Armillaria Root Disease. #2 - Diplodia Blight of Pines: This disease attacks pines and is most damaging to plantings of both exotic and native pine species in 30 Eastern and Central States. The fungus is seldom found in natural pine stands. Diplodia pinea kills current-year shoots, major branches, and ultimately entire trees. The effects of this disease are most severe in landscape, windbreak, and park plantings. Symptoms are brown, stunted new shoots with short, brown needles.More on Diplodia Blight of Pines . #3 - White Pine Blister Rust: 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.More on White Pine Blister Rust. #4 - Annosus Root Rot: The disease is a rot of conifers in many temperate parts of the world. The decay, called annosus root rot, often kills conifers. It occurs over much of the Eastern U.S. and is very common in the South.The fungus,Fomes annosus, usually enters by infecting freshly cut stump surfaces. That makes annosus root rot a problem in thinned pine plantations. The fungus produces conks that form at the root collar on roots of living or dead trees and on stumps or on slash. More on Annosus Root Rot. #5 - Fusiform Rust of Southern Pines: This disease causes death within five years of a tree's life if a stem infection occurs. Mortality is heaviest on trees less than 10 years old. Millions of dollars are lost annually to timber growers because of the disease. The fungus Cronartium fusiforme requires an alternate host to complete its life cycle. Part of the cycle is spent in the living tissue of pine stems and branches, and the remainder in the green leaves of several species of oak. More on Fusiform Rust of Southern Pines.