Thousand Cankers Disease Found in Knoxville, TN

Photo: walnut canker from Dr. Alan Windham, Extension Plant Pathologist, University of Tennessee

A black walnut (Juglans nigra) sample collected by Dr. Scott Schlarbaum, research forester at the University of Tennessee, has been confirmed as thousand cankers disease (TCD) (Geosmithia sp. nov.). Also found in the Knoxville TN walnut sample was one adult male beetle, verified as walnut twig beetle (Pityophthorus juglandis).

This is the first report of the walnut twig beetle and TCD in the native range of black walnut. TCD has killed thousands of walnut trees in the western United States and could potentially be devastating in the eastern United States as well. The extent of the outbreak in the Knoxville area is unknown at this time. The affected trees are in an urban area. Judging the sample, the disease has been present in the region for a number of years and is causing mortality.

Based on our experience TCD will be difficult, if not impossible, to stop. The hope is that the beetle and disease will behave differently in the eastern U.S. It takes 3-5 years to kill a large walnut tree. There are probably other outbreaks in the East that have not yet been noticed.

Dr. Alan Windham, UT Extension Plant Pathologist, urges foresters and others to be on the lookout for unusual dieback or mortality of walnuts, especially in urban areas. This is where TCD is likely to occur first because of movement of the beetle in wood (firewood, fresh lumber).

At this time the USDA has no federal quarantine on TCD, and this disease is not on any action lists. For further information, search: http://www.ppdl.purdue.edu/PPDL/pubs/walnutthousandcankersdisease.pdf

Aucuba -- the "Holly" of the Shade Garden

On a recent trip to the Knoxville Botanical Garden, I was re-introduced to a shrub, not used as much as it should be - gold dust plant (Aucuba japonica). Hardy to garden zones 6b-10, aucuba is at home in part sun to heavily shaded areas in the garden. Direct sunlight, even in the darker winter season, will scorch the foliage.
I've enjoyed a "plain green" foliage variety in my landscape over the past 16 years. It is tucked among three Japanese maples. Its holly-like leaves and bright red berries (on female cultivars)become more noticeable after the surrounding maples have surrender their fall plumage.

Many gold leaf cultivars sparkle in an otherwise dreary winter garden. Many cultivars abound. I particularly like 'Picturata', exhibiting large bright golden splotches in the center of each leaf and splashed by tinier yellow specks.

Branches on this 8-10 foot tall shrub are upright in habit. Growing culture is the same as hollies - preferring a well-drained, richly composted and moist soil site.