Minnesota First Detectors Oak Wilt Deadly Pathogen

Minnesota First Detectors Oak Wilt Impacts Distribution, status Biology, identification, and symptoms

Minnesota First Detectors Impacts Serious disease of oaks in the Midwest, eastern US and Texas Attacks all oak species Red oak group (northern pin, northern red, black) is very susceptible White oak group (bur, swamp white, white) is more tolerant

Minnesota First Detectors Distribution of oak wilt Range of oak wilt in US Range of oak wilt in Minnesota, 2006 DNR Aerial survey

Minnesota First Detectors 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 Range of red oak in Minnesota St. Croix State Park

Minnesota First Detectors Biology of oak wilt Fungal pathogen, Ceratocystis fagacearum Discovered 1942 in Wisconsin Now thought to be introduced, possibly from Central or South America or Mexico Spreads in two ways: overland by insects and underground through grafted roots

Minnesota First Detectors Oak wilt spore mats Fungus creates spore mat beneath bark of red oaks the spring after tree wilts Pressure pads form on mats that cause bark to crack Jenny Juzwik. Photo by Joe O’Brien, USDA Forest Service, bugwood.org

Minnesota First Detectors Overland spread Spore mats have fruity odor that attracts sap beetles 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

Minnesota First Detectors Biology of oak wilt 90% of oak wilt is spread by root grafts of trees within feet of each other Fungus travels through water- carrying vessels in roots to a healthy oak 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

Minnesota First Detectors Symptoms Tree “flags;” whole branches, parts of crown turn brown in July or August Leaves drop off Fungal mats under bark the next spring Sapwood streaking is not sufficient to diagnose Conclusive diagnosis from U of M Plant Disease Clinic

Minnesota First Detectors Identification: oak wilt v. bur oak blight Oak Wilt Water-soaked appearance Leaves fall off Tree wilts and dies in same season Fungal mats produced the following season Bur Oak Blight Wedge-shaped lesions between veins Leaves hang on Dark veins on underside, tiny black bumps on petioles Tree may live for years with symptoms

Minnesota First Detectors Identification: oak anthracnose Oak wilt may be confused with oak anthracnose Favored by cool, wet spring Symptoms appear more in lower branches Leaves have small to large brown areas; appear scorched Leaves drop Tree recovers over the season DNR photo

Minnesota First Detectors Identification: 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 (unlike OW)

Minnesota First Detectors 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, or Tarp firewood carefully, covering ends of tarp with soil, for one year after trees died Prevent underground spread Sever root grafts with vibratory plow line Preventative treatment of high-value urban oaks with fungicide

Minnesota First Detectors Other oak pest management Bur oak blight Promote tree vigor May treat with fungicide in early summer before leaf symptoms appear Oak anthracnose Rake up leaves to limit overwintering fungus Increase tree vigor Two-lined chestnut borer Prevention; promote tree vigor

Minnesota First Detectors Oak wilt is mainly transmitted by picnic beetles. A. True B. False

Minnesota First Detectors The leaves of a red oak with oak wilt hang on the tree from one season to the next. A. True B. False

Minnesota First Detectors Oak wilt can be managed by disrupting root grafts. A. True B. False

Minnesota First Detectors Questions?