Elm Yellows is a plant disease

Phytopathology

Plant pathology is the scientific study of plant diseases caused by pathogens and environmental conditions . Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants...

 of elm

Elm

Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the plant family Ulmaceae. The dozens of species are found in temperate and tropical-montane regions of North America and Eurasia, ranging southward into Indonesia. Elms are components of many kinds of natural forests...

 trees that is spread by leafhoppers or by root grafts. Elm Yellows, also known as Elm Phloem

Phloem

In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...

 Necrosis, is very aggressive, with no known cure. Elm Yellows occurs in the Eastern United States

Eastern United States

The Eastern United States, the American East, or simply the East is traditionally defined as the states east of the Mississippi River. The first two tiers of states west of the Mississippi have traditionally been considered part of the West, but can be included in the East today; usually in...

 and southern Ontario

Ontario

Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....

 in Canada. It is caused by phytoplasmas which infect the phloem (inner bark) of the tree. Infection and death of the phloem

Phloem

In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...

 effectively girdles the tree and stops the flow of water and nutrients. The disease affects both wild-growing and cultivated trees.

Importance

Elms are very important to the American landscape, prized for their unique shade characteristics. Most native elms are susceptible to Elm Yellows and there are few resistant cultivars. Large, healthy, landscaped elm trees can easily be worth thousands of dollars.
Penn State University is home to one of the oldest and largest elm stands in the country. Penn State has been battling Dutch Elm Disease

Dutch elm disease

Dutch elm disease is a disease caused by a member of the sac fungi category, affecting elm trees which is spread by the elm bark beetle. Although believed to be originally native to Asia, the disease has been accidentally introduced into America and Europe, where it has devastated native...

 for many decades, and the recent introduction of Elm Yellows into the PSU campus poses many threats. A tree near the president’s house had to be removed and numerous trees in the State College Borough have died or have been removed due to Elm Yellows.

Elm malls across the US are at risk to be destroyed by Elm Yellows. Cornell University

Cornell University

Cornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...

, for example, had a large elm collection which was being managed for Dutch Elm Disease, much like Penn State, and once Elm Yellows hit the campus, all of the elms were destroyed within a matter of years.

Transmission

The phytoplasma is transmitted by root grafts and leafhoppers. Root grafts, which occur among many species of trees happen when their roots fuse together and aid in anchoring the tree to the ground and provide more nutrient flow. Since elms are planted lining malls or streets Elm Yellows can travel directly from tree to tree, with out having to be transmitted by leafhoppers. Leafhoppers will feed on infected trees and move onto a healthy tree and infect it with the Mycoplasma-like bacteria through the bite marks. Transportation of nursery trees is another way for Elm Yellows to be spread over long distances. Fortunately, leafhoppers move very slowly so movement of Elm Yellows has been slow. Another possible vector for the disease is the spittlebug, but research is still being done to determine if it, indeed, transmits the disease.

Injury

When an elm is infected with Elm Yellows, the first thing to die is the root hairs. Root hairs are important because they are the main uptake for water and nutrients for the tree. Then the phytoplasma infection moves up the bark and infects the phloem, which will stop the tree from getting the nutrients it needs. The phloem is in charge of transportation of nutrients up the tree. Death of the phloem essentially strangles the tree to death. As the phloem is infected, it will change color and take on a wintergreen smell, similar to that of Black Birch or birch beer

Birch beer

Birch beer is a carbonated soft drink made from herbal extracts, usually from birch bark. It has a taste similar to root beer. Various types of birch beer are available, distinguished by color. The color depends on the species of birch tree from which the sap is extracted...

.

Control

Aggressive control is needed if trees show symptoms of being infected. Time is of the essence since nearby trees may already be infected. Removal and destruction of the infected tree is the first step. Then trenching around the next two rows of trees near it is needed. Trenching is when a deep ditch is dug to isolate infected areas. Trenching will sever root grafts and hopefully stop the transmission of the disease. Spraying trees with insecticide will also help reduce the chances of transmission. If the leafhopper is dead it will not be able to transmit the disease or damage the tree. Injecting trees with tetracycline antibiotics has been shown to slow the progress of Elm Yellows.

Planting one type of tree in one area is never a good idea. When landscaping an area it is important to vary the types of trees that are planted so that no one disease or pest can destroy all your trees at once.