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Insect and Disease Pests In Delaware’s Forests. Envirothon Training Updated October 2007 Glenn (Dode) Gladders. Symptoms  Changes in the plant’s appearance that indicate something is happening. Ex: crown dieback, wilting, cankers. Signs

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Insect and disease pests in delaware s forests

Insect and Disease PestsIn Delaware’s Forests

Envirothon Training

Updated October 2007

Glenn (Dode) Gladders

Symptoms vs signs


 Changes in the plant’s appearance that indicate something is happening. Ex: crown dieback, wilting, cankers.


 Indications of the insect or disease itself. Ex: frass, pitch tubes, fungal fruiting bodies.

Symptoms vs. Signs

The envirothon seven

Know these:

Emerald Ash Borer

Asian Longhorned Beetle

Southern Pine Beetle

Gypsy Moth

Sirex Wood Wasp

Bacterial Leaf Scorch

Sudden Oak Death

For each, know:


Present in Delaware?

Host species

Symptoms & Signs

Type of damage

Control measures


Emerald ash borer eab
Emerald Ash Borer (EAB)

Adults arebright greenand easy to identify.

  • Non-native

  • Has not been found in Delaware, but present in Maryland

  • A threat to ash trees only

  • Larvae create galleries in the cambium of infested trees, girdling the trees

Emerald ash borer eab1

D-shaped exit hole,

splitting bark


Emerald Ash Borer (EAB)



Crown dieback

Emerald ash borer eab2
Emerald Ash Borer (EAB)

  • Control in our area = ERADICATION

    (Remember, it has not been detected yet in Delaware)

  • Cut all ash trees in the area of new infestations. Chip the trunks and branches to a small size.

Asian longhorned beetle alb
Asian Longhorned Beetle (ALB)

  • From China

  • Has been detected in New York, New Jersey, not DE

  • Threatens numerous types of trees, particularly the maples.

Asian longhorned beetle alb1
Asian Longhorned Beetle (ALB)

  • The beetle develops within the xylem (wood) and then bores its way out. Eventually the many exit holes will destroy the cambium and kill the tree. The weakened wood can also cause structural failure (tree breaks in half).

Asian longhorned beetle alb2
Asian Longhorned Beetle (ALB)

  • Large exit holes are conspicuous signs of ALB infestation.

Asian longhorned beetle alb3
Asian Longhorned Beetle (ALB)

Infested trees must be removed,

and chipped to destroy all beetles.

Asian longhorned beetle alb4
Asian Longhorned Beetle (ALB)

Packing materials are inspected at ports of entry.

Southern pine beetle spb
Southern Pine Beetle (SPB)

  • Native

  • Present mainly in southern DE

  • Hosts are hard pines (all except white pine)

  • Chews galleries which can girdle trees. Also introduces a harmful fungus.

  • Delaware is at the northern end of its range. A more serious pest in the South.

Southern pine beetle spb1
Southern Pine Beetle (SPB)

  • Infested stands can be detected with aerial surveys. Infested pines display brown foliage.

Southern pine beetle spb2
Southern Pine Beetle (SPB)

Small round holes



Pitch tube

Southern pine beetle spb3
Southern Pine Beetle (SPB)


Infested trees can be cut and

burned, chipped, or sprayed.

Gypsy moth
Gypsy Moth

  • Non-native

  • Introduced into Massachusetts in 1869. Since then it has spread throughout the northeast, including Delaware.

Gypsy moth1
Gypsy Moth

  • Larvae feed on the leaves of many broadleaved species, particularly the oaks.

  • Host trees are damaged through defoliation.

Gypsy moth2
Gypsy Moth

  • When severe defoliation occurs several years in a row, widespread mortality can result.

Gypsy moth3
Gypsy Moth

Defoliation can be seen from the air during June survey flights

Egg masses

Gypsy moth4
Gypsy Moth

  • Egg masses are easily seen in the fall. These methods can determine the need for a control program the following spring.

  • Control = chemical sprays.

Sirex Wood Wasp

  • Non-native

  • Has not been found in Delaware

  • Threatens loblolly and other pines

  • Forms galleries that injure trees

  • Carries a fungus that causes more damage

Sirex Wood Wasp

Symptoms / Signs

Resin beads

Round exit holes

Wilting and discoloration

Sirex Wood Wasp


  • Control measures unknown (new pest)

  • Biological controls have been successful in other parts of the world

  • Early detection surveys in DE using trap trees

Red pine trap tree at White Clay Creek SP

Bacterial Leaf Scorch (BLS)

  • Control:

  • Native to the United States

  • Present throughout Delaware

  • Hosts = red oaks and other trees

    • Mainly northern red, pin, black, and scarlet oaks

  • Symptoms = Marginal leaf scorching in late summer and fall, dieback

Bacterial Leaf Scorch (BLS)

  • The bacteria are spread (vectored) by insects that feed on the xylem

  • Bacteria reproduce and physicallyclog the xylem

  • Simply a “plumbing” problem. Not enough water can move through the xylem to branches and leaves, so living tissues dessicate and die.

Bacteria clogging xylem

Bacterial Leaf Scorch (BLS)


Marginal leaf scorch


Bacterial Leaf Scorch (BLS)


  • No proven prevention

  • No proven cure

  • Treatment trials ongoing in Delaware and elsewhere

  • Do not plant northern red oak or pin oak

Sudden Oak Death (SOD)

  • Non-native

  • Has never been found in Delaware

  • Threatens oaks and other trees, as well as viburnums and other understory plants

  • Two types of symptoms:

  • Understory plants

    • Foliar scorching

    • Twig dieback

  • Overstory trees

    • Bleeding stem cankers

    • Dieback


Sudden Oak Death (SOD)

Understory plants

Overstory Trees

Twig dieback

Bleeding canker

Foliar symptoms


Sudden Oak Death (SOD)

  • Control:

  • No control in generally infested areas such as California

  • Control in other areas is quick response after detection. Cut, pile, and burn is an accepted prescription in new detection areas.

  • Quarantines are in place to prevent new introductions.