Tree Diseases

Urban Forestry

Plant: Elm Tree

Urban Forestry

Urban forestry

• The care and management of urban forests, (tree populations in urban settings) for the purpose of improving the urban environment

• Most urban trees are non-native and selected for particular aesthetic qualities

Elm Tree

• The American or White elm is the largest species of elm.  Usually over 100ft high.

• Due to its graceful form and size, it was an extremely popular urban tree before the spread of Dutch elm disease. 

• Once found mostly in eastern North America, remaining populations of mature American elms are concentrated in the American Midwest and Canadian Prairies.   

Dutch Elm Disease

• Dutch elm disease (or DED) is caused by a fungus. After the disease is contracted, spores rapidly reproduce and spread toxins throughout the tree.

• Fungus is spread by the elm beetle• The fungus blocks the vascular system of the tree

preventing water and minerals from reaching the branches and leaves.

• The leaves wilt and eventually the tree dies. • In Washington, DC, the disease has killed over 25,000

elms since 1950 with only 8,200 elms presently remaining on city streets.

Combating Elm Disease• Because Elms are such an important

urban species, much $ and effort goes into keeping them alive

• Fungicides are injected into the root flare• Disease resistant elms are often planted

as replacement trees. Washington DC tries to maintain the annual DED loss at below 2% of the remaining elm population.

Anthracnose

• Fungus that attacks hardwood shade trees• Kills the buds, damages the leaves and causes

premature leaf drop• Over time weakens the tree and makes it

susceptible to borers and other pest damage• Fungus overwinters in leaves on the ground. • Remove all fallen leaves and dispose of them• Treat by using fungicides• Tree on right was treated

Emerald Ash Borer

• Asian Beetle that bores under the bark of ash trees & lays eggs.

• The larva hatch and eat the cambium layer of the tree

• Has killed millions of trees around the great lakes and is moving south into WV, PA, & VA.

• Treatment is expensive and requires trained applicators.

Cankers

• Caused by fungus penetration of the bark

• Treatment – pruning below affected area

• Sterilize tools afterwards so as not to spread the disease.

Rust Diseases

• Cedar Apple Rust is biggest problem

• Affects crab apple trees and junipers

• Lives part of life cycle on each tree

• Destroy galls before April when they spread by spores

• Don’t grow cedars and apples close together

• Select resistant plants

Galls

• Growths that form on the leaves or stems of plants

• Can be caused by insects or viruses

• Rarely affect the overall health of a tree

• No treatment is required