Forest Diseases -- Test 3 -- Dutch Elm Disease

Other control recommendations include:

1. Use of resistant elms (species or varieties) 2. Use of insecticides to prevent bark beetle attacks 3. Biological control of bark beetles with a parasitic wasp (Dendrosota protuberans) or a fungus (Phomopsis oblonga) (used in England).

Additional management and control strategies of oak wilt

1.Chemical disruption of root grafts with Vapam 2. Removal of oaks within 50 feet of a diseased tree and treating stumps with a silvicide to prevent sprouting 3. Infected trees may be burned, chipped or buried 4. Girdle infected trees mechanically or chemically to reduce sporulation 5. Cut infected trees. Trees on the ground sporulate less than standing trees 6. Avoid cutting or pruning in spring and early summer to prevent attraction of nitidulid beetles. 7. Biocontrol with fungi has reduced sporulation but is not biologically or economically feasible.

Disease management recommendations:

Avoid planting Formosan sweetgum • Reduce injuries • Sterilize pruning equipment • Remove cankered branches

Oak Wilt

Ceratocystis fagacearum

characteristics of oak wilt as seen in aerial photographs

Circular areas or patches of dead trees (disease foci)

Chestnut blight is caused by

Cryphonectria parasitica

Which tree species is very susceptible to Endothia gyrosa

Formosan sweetgum

Mechanisms of wilt

Fungus (spores & mycelium) plug vessels • Fungus produces cell wall degrading enzymes • Fungus produces polysaccharides which increase water viscosity • Tyloses induced • Vessels collapse • Phenolic compounds induced • Gums induced • Embolism (air bubbles) induced

Symptoms of Endothia gyrosa

Large reddish orange stromata are formed on the canker surface

Symptoms of Chestnut Blight

Multiple cankers on stems and branches. Typically the bark splits and large areas of the bark collapse as cells die. Bark discolors and swells or collapses. The cambium turns brown as it becomes necrotic.

Endothia gyrosa causes

Native Endothia Canker

Damage while harvesting seed is common entry point of

Pitch Canker -- Mechanical injury as seen at the base of this tree is also a site of infection.

Fusarium circinatum causes

Pitch Canker fungus

Control of DED further involves

Sanitation to prevent bark beetles from invading dead branches or stacks of wood must be practiced. Pruning dead branches eliminates potential breeding sites. Removal of dead elms and their proper disposal is important.

Bark symptom of DED

Vascular browning (staining) of outer sapwood in trunk and stems

Hosts of Fusarium circinatum (a few)

Virginia pine Pitch pine Shortleaf pine

Bacterial Leaf Scorch

Xylella fastidiosa

Nectria Canker - Nectria species attack

a number of hardwood trees including dogwood

Infection courts of Pitch Canker are also found at

at the broken cone base formed when the cones are harvested.

The Nectria pathogen tends to fruit in the

bark-folds and crevices at the edge of the callous tissue that borders the canker

Nectria, also called Beech Bark Disease, is a disease complex involving the

beech scale insect Cryptococcus fagi and the canker-causing fungus Nectria coccinea var. faginata

Root grafts between diseased and healthy elms may be disrupted...

chemically or mechanically. These slides show the use of Vapam to chemically kill grafts between a tree with DED and two adjacent trees to prevent spread through root grafts.

Symptoms of oak wilt include

chlorosis, bronzing (necrosis) of leaves, flagging, wilting, premature leaf fall and death.

Chestnut blight has wiped out all the

commercial chestnuts and the understory species are replacing them

Bark on diseased oaks may be

cracked open by a structure produced by the fungus called a pressure pad.

In Chestnut blight Multiple sprouts are frequent following

death of the tree. Roots of the chestnut are not infected by the fungus.

Ascospores from Nectria perithecia are usually produced in

early spring and are wind-disseminated

Symptoms of Bacterial Leaf Scorch

edges of leaves browning as if they were scorched with fire

One means of control of oak wilt is to

eliminate root grafts between diseased and healthy trees.

Another obvious symptom of Pitch Canker is

excessive pitch flow from the canker and breakage at the point of the canker

DED was introduced into the United States on

imported elm burl logs in 1928

One means of dissemination of Ceratocystis fagacearum is by

insects. Here two sapfeeding beetles (nididulids) are feeding in the area of a pressure pad. Spores (conidia and ascospores) of the fungus are sticky and easily adhere to the body of the insect.

Control of DED involves

keeping elms far enough apart to prevent spread through root grafts. Alternate elms with nonsusceptible tree species

Bark beetles acquire the DED pathogen in

larval galleries as the adults emerges and carry spores to elm trees where they are deposited as the beetle feeds

Bacterial Leaf Scorch is spread by

leafhoppers

Vascular discoloration is typical of trees with

oak wilt. Note that the discoloration is limited to the outer sapwood region.

Spore (conidia) tendrils commonly form from the

pycnidia of chestnut blight

Another means of spread of this fungus (oak wilt) over short distances is through

root grafts

The DED pathogen can spread by

root grafts

Vectors of Bacterial Leaf Scorch are

sap feeders

Conidia (right) are disseminated by

splashing rain, squirrels and birds. Ascospores are wind disseminated

Redish orange _____________ form on the bark of the cankers

stromata

Elms can be treated by injection with a

systemic fungicide. This is effective if the chemical is applied before more then 5% of the foliage is showing symptoms and must be continued throughout the life of the tree.

Bacterial Leaf Scorch Spreads

systemically and causes slow decline and eventual death

Bacterial Leaf Scorch is found

throughout most of U.S.

Pitch canker frequently follows

tip moth damage resulting in a tip die-back symptom.

The scale insect alone can affect

tree vigor. The wounds that are inflicted serve as infection courts for Nectria coccinea var. faginata.

Various foliage symptoms of DED

wilting, browning of leaves and, eventually, defoliation

Bacteria of Bacterial Leaf Scorch are found in

xylem

Management Strategies of Bacterial Leaf Scorch

Control of vectors is futile Trunk injections with antibiotics sends trees into remission Mulching and irrigation delay symptoms Removal of trees for safety and aesthetic reasons

Management of Nectria

- Lady beetles are predacious on the scale insect but may not have a major effect on populations. • Insecticides are effective in landscape situations. • Removal of over mature trees and trees on steep slopes has resulted in partial reduction of damage. • Natural resistance in native beech trees has been reported and is a possibility for future management.