Status of thousand cankers disease on eastern black walnut in the eastern United States at two locations over 3 years |
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| Authors: | G J Griffin |
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| Institution: | Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, USA |
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| Abstract: | Thousand cankers disease (TCD), a lethal fungal dieback of eastern black walnut (Juglans nigra), caused by Geosmithia morbida, and spread by the walnut twig beetle, Pityophthorus juglandis, was documented in 2009 to be very destructive in the western United States and was identified in the native range of J. nigra at Knoxville, Tennessee, in 2010, and in 2011 at Richmond, Virginia. Beginning late 2010, we studied branch dieback levels (per cent live crown) and new TCD symptom development at these two quarantined locations monthly for 3 years. Of the 106 trees studied (53 at each location), 31 trees had low live crown ratings of 70 to 0% with little change over the 3 years of the study. One per cent of the trees developed new symptoms on a per‐year basis. Thus, a moderate level of TCD (mean = 76% live crown) was present in these two locations, and most trees were in a quiescent or dormant TCD condition for 3 years, an important finding not previously reported. We found new TCD symptoms developed in Richmond in 2011 and 2012 when precipitation from January 1 to the end of August was low (60–64 cm), and not when the precipitation in Richmond was higher (99 cm). In late 2012, in Richmond, soil water potential assays indicated that some black walnut trees were under severe physiological stress (?15 bars). In contrast, in 2013, high precipitation levels (99 and 130 cm) and high soil water potentials (?0.1 to ?3 bars) at both locations were associated with extensive new foliage and stem growth and recovery from TCD. Further research is needed on water relationships in regard to TCD and black walnut health. |
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