Tobacco Disease Information Note 2
T. A. Melton, Philip Morris Professor and Department Extension Leader
H. D. Shew, Professor of Plant Pathology
Year after year Granville wilt continues to be one of the most destructive
diseases of tobacco in North Carolina. It causes losses from over 1 to
2% of the entire tobacco crop, costing growers from $10 to $15 million
annually. Granville wilt was first observed in 1880 on a few farms in
the Northern areas of North Carolina's Middle Belt. During the next 30
years losses from this disease increased on farms in Granville, Vance,
Wake and Durham counties to the point where it was causing 25 to 100%
field losses. During that period this disease caused banks to close, farms
to be sold, and towns to decline. Today it not only plaques the Middle
Belt but is the most chronic disease problem in eastern North Carolina
and in the Border Belt. Its more recent extension into the Old Belt also
has made Granville wilt a statewide problem.
wilt is most damaging in fields where tobacco was grown the previous year,
in wet areas in a field, and in years where soil temperatures are normal
to above normal. Other plants the bacteria can infect include tomatoes,
Irish potatoes, pepper, eggplant, peanuts, and weeds.
The first symptom is a wilting on one side of the plant. As the disease
progresses, the entire plant wilts and death generally follows. When death
does not occur, plants are usually stunted and leaves may be twisted and
otherwise distorted. The stalk usually turns black, especially at the
ground level. At this stage, Granville wilt may be easily confused with
other diseases such as black shank. Dark streaks can be seen extending
up the plant just beneath the outer bark. Infection may not be noticed
immediately because wilting symptoms may not appear until the plant undergoes
moisture stress. It is not unusual to observe symptoms several weeks after
initial infection. A simple diagnostic test for Granville wilt can
be done on-farm. When an infected stem segment is suspended in a glass
of clear water for a few minutes, bacterial streaming occurs. The bacterial
streaming appears as white ooze or a smokey stream, which originates from
the cut end of the stem, where the dark streaks are observed under the
bark, and slowly moves out into the water.
Granville wilt is caused by microscopic bacteria (Ralstonia solanacearum).
The bacterium is spread by anything that moves infested soil or water.
Major means of spread include water, infected transplants and farm vehicles
moving from field to field. The motile bacteria gain entry into
the plant through natural openings or wounds. Since roots often "wound
themselves" as they grow, or are wounded during transplanting, the
Granville wilt bacteria have no difficulty in gaining entry into the plant.
More extensive root wounding caused by nematodes or root pruning during
cultivation provide more paths of entry for the bacteria. Increased disease
levels in the resistant varieties have been noted where root-knot nematodes
are present. High populations (greater than 250,000 bacteria per gm of
soil) are usually necessary for infection to occur. The bacteria
may also be spread during mechanical topping and harvesting. These bacteria
are favored by relatively high soil temperatures and adequate to high
moisture levels in the soil. Poor soil drainage and wet, warm growing
seasons favor Granville wilt.
Crop Rotation - Crop rotation must be the basis on which Granville
wilt management programs are established. This practice is perhaps the
most essential thing that growers can do to minimize losses due to Granville
wilt. In fact, without appropriate crop rotation it is not possible to
manage this disease successfully where the infestation level is moderate
to high. Therefore, crop rotation must be the basis on which Granville
wilt management programs are established. Crop rotation is effective because
the Granville wilt bacteria live in the soil and are not well adapted
to survival in the absence of susceptible plant tissue. Thus, their populations
decline if a suitable plant such as tobacco is absent for even one year.
As is true with any other soil-borne pathogen, the longer the rotation,
the more efficient the control. However, planting a non-host crop (soybeans,
fescue, corn, cotton, milo) just one year will usually significantly reduce
the disease loss in the following tobacco crop. Integrating other management
practices, such as improved drainage, avoiding late or deep cultivations,
stalk and root destruction, and the use of multi-purpose fumigants where
disease occurred in past years, is better than relying on any one or two
and Root Destruction (R-9-P) - Roots and stalks from the previous
crop should be destroyed as soon as possible after harvest. The decay
of old plant residue through stalk and root destruction soon after harvest
decreases the number of bacteria present in the soil.
Varieties - Varieties are available which carry varying levels of
resistance to Granville wilt. None of these varieties is immune to this
disease and some losses might be expected in severely infested areas with
the use of any variety. Nevertheless, growers have an opportunity to select
those varieties which will afford them, in most cases, good protection
when used in combination with other disease control practices such as
stalk and root destruction and crop rotation. Consult the most recent
issue of the Tobacco Information bulletin, available in local county extension
centers, for resistance ratings of currently available varieties.
Control - The fumigants Chlor-O-Pic 100, Telone C-17, and Terr-O-Gas
67 may help control Granville wilt if used in combination with other cultural
control practices. All require a 3-week waiting period between time of
application and transplanting. Always read and follow label instructions.
Consult the most recent issue of the Flue-Cured Tobacco Information, available
in local county extension centers, for more information.
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with a specific problem, contact your local North
Carolina Cooperative Extension Service personnel.
of specific chemicals are based upon information on the manufacturer's
label and performance in a limited number of trials. Because environmental
conditions and methods of application by growers may vary widely, performance
of the chemical will not always conform to the safety and pest control
standards indicated by experimental data. All recommendations for pesticide
use were legal at the time of publication, but the status of registration
and use patterns are subject to change by actions of state and federal
regulatory agencies. Last printed 04/91
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in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment
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Web page last updated Dec. 2000