Bright yellow, wilted tobacco plants often make producers concerned about black shank, but we have seen a number of tobacco samples submitted to the Plant Disease Diagnostic Lab in which tomato spotted wilt (TSW) was the culprit. Dr. Pearce reports seeing TSW during recent field visits as well. Tobacco infected with the TSW virus may show “classic” symptoms of leaf distortion, ringspots, and veinal necrosis (Figure 1), but less striking symptoms such as plant stunting, yellowing, wilting, and necrotic lesions on the stems may also occur. Plants infected early (before or just after transplanting) may wilt and die rapidly before foliar symptoms are obvious.
Although we normally expect TSW incidence to be low in a given field (around 2% or less), we have had at least two lab samples in which incidence was estimated at 15% or greater. If other diseases or abiotic factors accounted for some of the symptoms in these fields, those problems were not represented in the sample material.
In some cases, multiple diseases have been present in samples submitted to the lab. See the image below (Figure 2) of plants from the same field. Both had leaf yellowing, but other foliar and stem symptoms differed. The Extension agent correctly observed symptoms of two different diseases and submitted both for diagnosis. Ringspots on stems and leaf distortion clearly indicated TSW (plant on left); dark, basal stem canker and leaf yellowing were more suggestive of black shank or soreshin (plant on right). In fact, lab tests confirmed both soreshin (Rhizoctonia solani) and TSW on the plant with basal cankering. Black shank was not present. Similar symptoms have been seen on dark tobacco samples with TSW from western Kentucky (Figure 3).
There are no curative or rescue treatments for TSW. However, secondary spread within a field is usually low. For information regarding management of tobacco diseases, refer to UK Extension publication, Tobacco Production Guide (ID-160).
Additional information about TSW can be found at the University of Georgia Tomato Spotted Wilt Virus Web page.
By Julie Beale, Plant Disease Diagnostician & Bob Pearce, Extension Tobacco Specialist