Life in the Tension Zone
Sue Eiler
2011-09-15
A wide swath sweeps across the state, known as the tension zone and we happen to be right in it. Southern prairies and oaks give way to northern pines and hardwoods, and animals take advantage of the abundance. Remnants of bur oak, a hardy prairie tree stand next to walnuts, just barely thriving this far north. Factors beyond climate challenge our trees as a host of diseases and insects weaken and kill some of our favorite trees. Linda Williams, Forest Health Specialist - Northeast Region, WDNR, has this information to share:
Thousand cankers disease of walnut - The disease is caused when Walnut Twig Beetles, which can carry the fungus (Geosmithia morbida), tunnel beneath the bark of walnut trees. The fungus then causes small cankers to form. As more beetles attack the tree, introducing more fungus, the number of cankers increases, slowly starving the tree of nutrients and causing the tree to die within 10 years of initial infestation. There is no known cure.
The first known location of this disease east of the Mississippi was in Tennessee and has been detected for the first time in Pennsylvania. If you think you have found Thousand Cankers Disease on walnut in Wisconsin please alert your forest health specialist immediately. This disease could occur in urban trees, plantations, or natural forests so please be vigilant.
Bur Oak Blight - BOB is believed to be caused by a new species of Tubakia. Tubakia dryina has been known to be the causal agent of Tubakia leaf spot. However, BOB is considered a blight disease, than a leaf disease. In a severe case, all leaves on a tree will die late in the season. Symptoms of BOB have been reported in the Upper Midwest since 1990's, including Kansas, Iowa, Minnesota, Nebraska, and Wisconsin. Trees may be able to sustain repeated defoliation because it starts late in the season, though secondary pests may kill trees that are stressed by repeated infection with BOB. It’s important not to misidentify BOB as Oak Wilt, or vis-a-versa.
Oak Wilt symptoms - Oak wilt is a non-curable fungal disease specific to oaks. Trees in the red oak family will die quickly and completely from this disease while trees in the white oak family will die more slowly with a branch or portion of the crown becoming infected. Trees that were infected with the oak wilt fungus this year are currently turning off-color, dropping their leaves, and will soon be dead. Leaves that drop to the ground will be partially green. Once a tree is infected with oak wilt the fungus will begin to spread outward from the roots of the infected tree through root grafts and into the roots of neighboring trees. In this way, over several years, a pocket of dead oaks will be created and the disease will continue to spread through the roots unless something is done to break the root grafts, or, it will stop when the disease runs out of oaks in that area
Eastern Spruce Gall Adelgid - Swollen areas on the twigs of spruce trees may look like small cones but they're homes for small adelgids which live inside the gall and suck plant juices. For part of their life, adelgids live within these galls that the tree creates for them. As fall approaches the galls will turn brown, dry out, split open, and release the adelgids. Old adelgid galls will remain on the tree for the life of that branch. The galls do not usually kill the branch although severe infestations can stunt the growth of the tree and predispose it to attack from other insects or diseases. Eastern Spruce Gall Adelgid prefers to attack white spruce and Norway spruce. Another adelgid, Cooley Spruce Gall Adelgid, prefers blue spruce and makes larger galls at the tips of twigs.
Rhizosphaera needlecast - calls continue to roll in about spruce that are severely affected by rhizosphaera needlecast. I suspect that the "wettest July on record" that we had last year contributed to the damage, and the prolonged wet, cool spring that we had will just continue to promote the disease. Many of the folks that are calling in say that they have never seen these symptoms on their trees before (although I suspect a more accurate description is that the symptoms have never been this noticeable or this severe). The most severely affected trees around the region are blue spruce, and this can be a somewhat common malady for these trees, whether they're planted in a yard or in a plantation, but white spruce are also severely affected around the region as well.
