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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Deciduous Trees > Oak > Dead branches or branch dieback

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Oak > Trunk/Branches > Dead branches or branch dieback

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  • Image: Twolined chestnut borer 1
  • Image: Twolined chestnut borer 2
  • Image: Twolined chestnut borer 3

Twolined chestnut borer
Agrilus bilineatus

  • Leaves in upper canopy look wilted, turn brown but remain attached to branch for several weeks
  • 1/8 inch D-shaped exit holes
  • S-shaped galleries underneath bark
  • Bluish black bodies with two light stripes running down the wing covers
  • Larvae are approx. 1 inch long and white with 2 spines at abdomen tip
  • Damage visible mid to late summer
  • More information on twolined chestnut borer...
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  • Image: Armillaria root rot 1
  • Image: Armillaria root rot 2
  • Image: Armillaria root rot 3

Armillaria root rot
Armillaria gallica and Armillaria spp.

  • Infected trees have poor growth, dead branches in the upper canopy, undersized and/or yellow leaves
  • Flat white sheets of fungal mycelia (mycelia fans) grow between the bark and sapwood at the base of infected trees
  • Thick black, shoestring-like fungus can sometimes be seen under the bark, around roots and in the soil around the base of the tree
  • Wood is decayed, white, soft and spongy, and this may extend from the base of the tree well up into the trunk
  • Trees frequently break or fall over in storms
  • Clusters of honey-colored mushrooms may grow at the base of the tree in fall
  • Twolined chestnut borers often found on trees affected by Armillaria root rot
  • More information on Armillaria root rot...
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  • Image: Stem girdling roots 1
  • Image: Stem girdling rootsStem girdling roots 2
  • Image: Stem girdling roots 3

Stem girdling roots

  • Affected trees commonly exhibit excessive and abnormal winter damage including frost cracks and dieback
  • A root circling the trunk of the tree may be seen at the soil line
  • Trunk may be sunken in or compressed where it contacts the root
  • If girdling root is below ground, the trunk will lack the natural widening or flare at the soil line so will go straight into the earth like a telephone pole; trees often exhibit an abnormal lean
  • Affected trees are often stunted, exhibit poor summer color, change color and lose their leaves early in the fall
  • Affected trees commonly exhibit water-stress symptoms such as marginal leaf scorch, wilting, sudden leaf fall
  • More information on Stem girdling roots...
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  • Image: Lightning injury 1
  • Image: Lightning injury 2
  • Image: Lightning injury 3

Lightning injury

  • Continuous, sporadic or twisting, vertical stripping from bark torn away on main stem or other large branches
  • Cracks or splits in bark from lightning strikes begin in the canopy and extend to the ground line
  • Often, large pieces of wood strewn about the hit tree
  • Death more common on trees within red oak group; strikes more common when oaks are tallest in area
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  • Image: Ganoderma butt rot 1
  • Image: Ganoderma butt rot 2
  • Image: Ganoderma butt rot 3

Ganoderma butt rot
Ganoderma applanatum

  • Leaves are smaller in size and turn yellow earlier than normal
  • Canopy appears thin with few leaves and multiple dead branches
  • Fungal conks, a semicircle shelf fungi, can be found from the base of the tree up to 3 feet high on the trunk
  • Conks are reddish brown and shiny on top, white and porous underneath, a rim of white may be visible on the edge of growing conks
  • Infected wood at the base of the tree is white, soft, stringy or spongy
  • Infected trees frequently break or fall over in storms
  • More information on Ganoderma butt rot...
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  • Image: Heart rot 1
  • Image: Heart rot 2
  • Image: Heart rot 3

Heart rot
Laetiporus sulphureus, Phellinus everhartii, Phellinus
igniarius, and others

  • The canopy may show no symptoms or may have small yellowing leaves or dead branches depending on the extent of the trunk decay
  • In cross section of the trunk, the wood at the center is discolored, soft, crumbling, stringy or spongy
  • Fungal fruiting bodies arise along the stem, near a pruning wound, crack or other wound
  • Many shapes and sizes of fungal fruiting bodies may be seen
  • Phellinus spp. have hoof shaped fruiting bodies that are black on top and yellow brown underneath
  • Laetiporus sp. have folds of yellow to bright orange fungal tissue arising in a clump
  • More information on Heart rot...
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  • Image: Deicing salt injury 1
  • Image: Deicing salt injury 2

Deicing salt injury

  • Soil salt damage causes leaf edges or margins to appear burnt or scorched progressing toward the mid-vein
  • Soil salt damage can mimic nutrient deficiencies, e.g., yellowing foliage on deciduous plants
  • Salt spray causes branches to become tuft-like (a.k.a. witches’ broom)
  • Run-off salt kills roots which results in die-back of most branches
  • Affected trees leaf out later than other non-infected trees
  • All deicing damage most noticeable in spring
  • More information on Deicing salt injury...

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