Chinese (Kousa) Dogwood Doesn't Like Extreme Heat

photo: leaf curl on kousa dogwood
Never forget the adage: "the right plant in the right location". In USDA hardiness zone 7 and warmer parts of zone 6-b, Chinese dogwood (Cornus kousa) does not cope with excessive summer heat well. A typical stress response is leaf curling. On more stressful droughty sites, leaf margins and centers will likely burn.

The young tree pictured above is planted along a suburban street, with a concrete sidewalk and street curb on two sides. Thick turf sod covers the ground beneath the tree, competing with the tree for available soil moisture and nutrients. On a hot 90°F day, this tree is likely to experience heat indices above 120°F.

Likely, the tree will survive, but not bloom dependably every spring. Leaf burning and curling reduce the tree’s ability to photosynthesize, resulting in less (or more) flower bud set. The tree will either flower poorly or bloom heavily in future springs, resulting in an alternate flowering cycle or "biennial bearing".

Kousa dogwood will handle full sun locations, provided heat and drought stresses are managed through timely irrigation. Currently, the University of Tennessee is evaluating several seedling kousa selections for better heat and drought tolerances here in the mid-South.

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