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Oak Wilt

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Oak Wilt

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  1. Oak Wilt Ceratocystisfagacearum

  2. Oak Wilt • Impacts • Distribution, status • Biology, identification, and symptoms

  3. Distribution of oak wilt • Found in the Midwest, eastern US and Texas • Discovered 1942 in Wisconsin • Now thought to be introduced, possibly from Central or South America or Mexico Range of oak wilt in US

  4. Distribution of oak wilt • First found in MN in late 1940’s Range of oak wilt in Minnesota, 2006 DNR Aerial survey

  5. Status • 2011: oak wilt discovered in St. Croix State Park in Pine County • Most northern find to date • Also found outside the park at a residence • Want to keep it from spreading throughout the oak resource St. Croix State Park Range of red oak in Minnesota

  6. Biology of oak wilt • Fungal pathogen of all oaks • Spreads in two ways: overland by insects and underground through grafted roots • Red oak group (northern pin, northern red, black) is very susceptible • White oak group (bur, swamp white, white) is more tolerant Jenny Juzwik, US Forest Service Red oak

  7. Oak wilt spore mats • Fungus creates spore mat beneath bark of trees in the red oak group (pointy edges) the spring after tree wilts • Mats rarely develop on species of white oak (rounded edges) Jenny Juzwik. Photo by Joe O’Brien, USDA Forest Service, bugwood.org Cut-away revealing spore mat

  8. Bark cracks • Pressure pads form on spore mats, causing bark to crack • Cracks difficult to see • Spore mats have fruity odor that attracts sap beetles to the cracks Joe O’Brien, US Forest Service, bugwood.org

  9. Overland spread • Sap beetles pick up sticky fungal spores from mats • Fly to uninfected but wounded tree (e.g., from pruning or storms) • Beetles transfer fungal spores through tree wound Sap beetle

  10. Underground spread • Oak wilt also spreads through underground root grafts • Root grafts account for 90% of the spread of oak wilt in an infection center • Neighboring oaks can have common root systems • Oaks of different species graft very rarely Jenny Juzwik, US Forest Service

  11. Biology of oak wilt • Fungus travels through water-carrying vessels • Tree tries to stop fungus by producing a gummy substance that clogs water vessels • Lack of water flow causes leaves to wilt rapidly and fall off Joe O’Brien, US Forest Service, bugwood.org

  12. Symptoms • Tree “flags”: whole branches, parts of crown turn brown in July or August • Leaves of red oaks drop off • Visible “line” between green and brown on leaves • White oaks more tolerant; survive a year or more while displaying symptoms White oak. Jenny Juzwik, US Forest Service Red oak. Jenny Juzwik, US Forest Service Joe O’Brien, US Forest Service, bugwood.org

  13. Symptoms • Fungal mats under bark or red oaks the next spring; diagnostic for oak wilt • Streaking in sapwood, but not diagnostic • Conclusive diagnosis from U of M Plant Disease Clinic Fred Baker, Utah State Univ., bugwood.org

  14. Look-alike:bur oak blight • Only infects bur oaks • Wedge-shaped lesions between veins • Dark veins on underside, tiny black bumps on petioles • Some leaves hang on in winter; healthy bur oaks shed leaves in fall • Tree may live for several years with symptoms

  15. Look-alike: oak anthracnose • Favored by cool, wet spring • White oaks most severely infected • Symptoms appear more in lower branches • Leaves have irregular brown areas; appear scorched • Leaves drop • Tree recovers over the season DNR photo

  16. Look-alike:two-lined chestnut borer • Adults attack oaks stressed by drought, defoliation or construction • Symptoms and signs similar to EAB (same genus) • Characteristic pattern of multi-year attack: “Dead, Red, and Green” • Red oak leaves stay on tree

  17. Oak Wilt Management • Prevent above-ground spread through firewood • Mats may form on cut, bark-on firewood • Debark or use firewood within 8-9 months from wilting • Tarp firewood carefully, covering ends of tarp with soil, for one year after trees died

  18. Oak Wilt Management • Prune oaks in late winter • We now say “Don’t prune in April, May or June”

  19. Oak Wilt Management • Preventative treatment of high-value urban oaks with fungicide • Prevent underground spread • Sever root grafts with vibratory plow line Joe O’Brien US Forest Service, bugwood.org Ron Billings, Texas Forest Service, bugwood.org

  20. Oak wilt is mainly transmitted by picnic beetles. • True • False

  21. The leaves of a red oak with oak wilt hang on the tree from one season to the next. • True • False

  22. Oak wilt can be managed by disrupting root grafts. • True • False

  23. Questions?