Oak Wilt

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Oak Wilt

• D.L. Clement
• Regional Specialist
• University of Maryland Extension

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Oak Wilt

• Oak wilt was first described in Wisconsin in 1944
  where trees were found dying in localized areas.
  This disease kills young and mature oak trees and
  has been found in 21 states. The predominant
  damage has occurred in the upper Midwest although
  the range extends from New York to Texas.
•  

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Distribution of Oak Wilt2005
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Oak Wilt
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Oak Wilt

• Biology
• The fungus can overwinter as mycelial mats under
  the bark.
• As the fungal mats enlarge, they cause the bark
  to split and the emitted odor, which smells like
  apple cider, attracts bark and sap beetles that
  feed on the fungal mats.
• The beetles move the fungal disease from diseased
  trees to healthy trees beginning in the spring
  through feeding and reproduction activities.
• Trees can also become infected through root
  grafts between infected and adjacent healthy
  trees.
• Once inside the trees the fungus spreads rapidly
  inside the water conducting tissues of the xylem
  causing them to become plugged and nonfunctional.
  

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Oak Wilt

• Things to look for
• Red oak symptoms can occur as early as May with
  leaves turning dull green or bronze before
  wilting and becoming yellow or brown.  These
  symptoms typically affect the leaf tip and
  margins first as they move inwards towards the
  midrib and leaf base.  Wilted leaves will curl
  around the leaf midrib.
• Dying red oak leaf symptoms often intensify
  within a few weeks throughout the canopy and the
  leaves at the ends of the branches show heavy
  defoliation.
• Leaves will fall in all stages of symptom
  development.  Even apparently healthy green
  leaves will be shed as trees begin to decline.
• Severely diseased red oaks can die within 2
  months and most die within a year of visible
  symptoms.
• White oaks often have less severe symptoms and
  may only lose one or two branches a year. 
  Infected white oaks often have discolored annual
  rings, but seldom develop fungus mats under the
  bark.  Some white oaks may even recover and serve
  as symptomless reservoirs for this disease.

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Oak Wilt

• Host Trees
• This disease attacks all oak species and has been
  found in 16 native oak species.  In general, red
  oaks are more frequently infected compared to
  white oaks.  Additional inoculations have
  demonstrated over 35 native and exotic oak
  species are susceptible as well as American and
  European Chestnuts, chinkapin and tan oaks and
  several cultivars of apple. 

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Oak Wilt
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Oak Wilt
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Oak Wilt
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Oak Wilt

• Dark streaks under the bark of infected branches.