Elm Yellows

Elm Yellows is a plant disease of elm trees that is spread by leafhoppers or root grafts."Elm Yellows." Elmcare.Com. 19 Mar. 2008 . ] Elm Yellows, also known as Elm Phloem Necrosis, is very aggressive and there are no known cure for it. Elm Yellows is known to occur in the Eastern US and Southern Ontario. It is caused by phytoplasmas which infect the phloem (inner bark) of the tree.Price, Terry. "Wilt Diseases." Forestpests.Org. 23 Mar. 2005. 19 Mar. 2008 . ] Infection and death of the phloem effectively girdles the tree and stops nutrient and water flow.

Importance

Elm trees are very important to the American landscape since they are 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 for many decades, and the recent introduction of Elm Yellows into the PSU campus poses many threats.Ruskin, Paul. "Penn State Prepares for 'Elm Yellows' Disease." PSU Live 12 Nov. 2007.19 Mar. 2008 .] 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, 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 fungus 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.

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.

References

See also

* plant pathology