NEBRASKAland Magazine is dedicated to outstanding photography and informative writing with an engaging mix of articles and photos highlighting Nebraska’s outdoor activities, parklands, wildlife, history and people.
Issue link: http://mag.outdoornebraska.gov/i/654753
APRIL 2016 • NEBRASKAland 17 By Julie Van Meter State Entomologist, Nebraska Department of Agriculture Nebraska's black walnut trees (Juglans nigra) are at risk from a pest called Thousand Cankers Disease of Walnut (TCD). This pest has not been found in Nebraska, but threatens the state's black walnut trees. TCD is caused by a combination of the walnut twig beetle (Pityophthorus juglandis) and a fungal disease (Geosmithia morbida). The beetle is native to the southwest U.S., where it is a minor pest of Arizona walnut (Juglans major). The fungal spores are carried on the body of the beetle, and infect the tree as the beetle tunnels through the bark. Each infection site becomes a small canker. These grow and coalesce, creating very large cankers which girdle the tree and ultimately kill it. The walnut twig beetle is very small, and because of their small size, their exit holes are extremely difficult to see on tree bark. It is easier to look for the disease symptoms, which include yellowing and thinning of the tree canopy, and wilting of foliage. Dark cankers form under the bark, around the tunneling of the beetle, and may cause a dark stain on the bark surface. It is difficult to differentiate many of these symptoms from other causes, such as drought. The native range of black walnut extends from the east coast through the South and Midwest, to the eastern edge of the Plains states. In Nebraska, black walnut can be found in the eastern part of the state, primarily in riparian areas. This includes forests along the Missouri River, and rivers and streams leading into the central part of the state. Black walnut is a very important part of the native ecosystem in Nebraska. The nuts are utilized by many animals, from squirrels to turkey to deer, for food. Insects, including the caterpillar of the Luna butterfly (Actias luna) feed on walnut foliage. Additionally, black walnut contributes economically to the state through the harvest of both timber and nuts. Should TCD become introduced to Nebraska, the results could be devastating. Firewood is recognized as an excellent means of transporting damaging plant pests from one location to another, and walnut firewood could easily bring TCD into Nebraska. Infested logs and burls are another potential pathway for disease spread. Because of this, the Nebraska Department of Agriculture (NDA) has enacted a TCD quarantine, prohibiting the movement of certain items, including walnut trees, wood, and all hardwood firewood, from known TCD infested states. The full text of the quarantine and a list of specific regulated articles can be found on the NDA website at www.agr.ne.gov. th th th th t e tr tr tr tr tree ee ee ee an Th Th Th The wa wa w l and becau Bug Banter Presented by Black Walnut Trees in Danger