Dennis Fulbright*, Chrissy Mctavish and Andrew Jarosz

Spruce Decline and Its Causes

January 7, 2014 8:00 – 8:50 am

Dennis Fulbright*, Chrissy McTavish** and Andrew Jarosz** *Dept. Plant, Soil and Microbial Sciences, College of Agricultural & Natural Resources **Dept. Plant Biology, College of Natural Science Michigan State University

Today you will hear about a disease called spruce decline that is impacting the growth and health of spruce trees around Michigan. It is manifested by a slow, but continuously progressing needle and branch death that we are calling spruce decline. These symptoms usually occur first on the north and bottom branches of the trees, but progression usually continues until most of the tree is involved. Spruce decline has not impacted all spruce, which is interesting in itself, but appears to be more severe on certain species of spruce and on certain individuals within groupings. Therefore, not all spruce trees are dying and not all species are impacted equally. However, there are places where spruce trees are seriously impacted and landowners are choosing to limb-up spruce trees or remove them. You will hear our presentation today on known diseases of spruce and new diseases of spruce and why we believe some are more important than others in the disease we are calling spruce decline. Current funding supporting pesticide application research for potential management of spruce decline has been provided by the Michigan Dept. of Agriculture and Natural Resources/Hort Fund Program. Today, we will discuss various diseases of spruce. We will talk about needle cast diseases and canker diseases of spruce. You should know the difference by the end of the presentation. Needle cast diseases of spruce Needle cast diseases occur when certain fungal species or “pathogens” infect needles of spruce in the spring, live in the needle all summer, fall and winter, finally producing reproductive structures the following spring (a year after infection of the needle). The spores of the fungus will spread to new needles emerging after the reproductive structures form and sometime later the needle, with the fungal reproductive structures, will die and drop to the ground (cast). The branch rarely dies even though older needles fall off the branch. There is usually a new bud forming on the terminal of the branch. There are known needle cast pathogens of spruce, and some that are still questionable as to their ability to cause needle cast disease. Canker diseases of spruce A canker is an infection of twigs, branches or the main stem of the spruce tree. Cankers usually kill the stem tissue including bark, vascular tissues and cambium (the growing cell layer that encircles all stems). A canker usually leaks sap and produces an indentation of the stem that looks like a depression. If the canker enlarges such that it encircles the stem, it will girdle the stem and kill the stem, especially that portion of the stem to the outside of the tree (distal portion). Cankers of some trees do not encircle the branch, but so many cankers appear on the branch that the vascular system ceases to function and the branch dies. There is a known canker causing fungus on spruce called Cytospora that causes cankers and that has been thought to be the worst canker disease of spruce. However…… Today, we will present data that strongly suggests that known needle cast diseases and Cytospora canker are not the primary causes of spruce needle and branch death that we call spruce decline. Those diseases can still be found on spruce, but other fungi are now infecting spruce trees in nurseries, on tree farms and in the landscape that cause needle cast and branch death leading to spruce decline. The two fungal species that we believe are causing spruce decline are Phomopsis and Diplodia. You will hear a lot about Phomopsis and Diplodia in today’s presentation. Phomopsis is a known pathogen causing branch death in young nursery trees and sometimes on tree farm trees, but now we are finding Phomopsis causing cankers on large landscape trees. Diploida, known primarily as a pathogen of pine trees, also appears to be involved in spruce decline. Disease triangles Diseases are the outcome of three factors, the pathogen—the agent that causes the infection; the host—the plant on which the infection occurs; and the environment—the conditions that affect the establishment of the infection. All three of these are interacting at all times. Ask yourself, if the spruce trees that have been planted in Michigan for decades are beginning to show a new disease, and if the pathogens are not new invasive fungi, what else could have changed? Trees that have been in place for years are beginning to show signs of spruce decline--why? The pathogens have been here and the host has been here. The only leg of the triangle that could have changed is the environment. The future can be positive We are beginning to focus on fungicide management and natural resistance to shift the balance more toward the health of the tree. These will be directions we pursue in future years.