Wet 2013 Season Limits Tobacco Yields
“Weather-related problems from excess moisture seen in 2013 tobacco crop”
PRINCETON, KY.
Many experienced growers will tell you that with tobacco, a dry
season will scare you but a wet season can kill you. There is some basis
to this, as the tropical origin of tobacco likely makes the crop much
more tolerant of drought than of excessive moisture. We have seen both
extremes in the last two years with the extreme drought of 2012 and the
wet season of 2013. See table 1 for a summary of rainfall totals during
the tobacco field season (April to September) in 2013 compared to 2012.
The 50-year historical average rainfall for April-September for most
areas of the dark tobacco production area of west Kentucky and Tennessee
is about 23.75 inches. As shown in Table 1, rainfall at Princeton,
Mayfield, and Russellville KY was well below this historical average,
and was less than half of this average at Mayfield. 2013 was a major
contrast, with all three locations having well above average rainfall
for this period, and Russellville having nearly twice the average.
With tobacco, a wider variety of weather-related problems occur in a
wet season compared to a dry season, so several things are worth
remembering for the next wet season. Beginning early in the year when
ground preparation starts, risks of soil compaction are more likely in a
wet season. Soil compaction has been more common regardless of rainfall
in the past several years, as tobacco farms have gotten larger and
growers have more acreage to cover, resulting in more of a tendency to
work ground when it is too wet. Significant soil compaction can occur as
shallow as 6-inches or less from the soil surface even with relatively
small equipment and implements used on soil that is too wet to work.
Under these conditions, tobacco may develop healthy roots laterally from
the root ball and from the stem above the root ball with very little
root growth downward due to the compacted zone. A good method to
determine if the ground is too wet to work is to form a soil ball in
your hand. If the soil remains as a firm ball when you release it, the
soil is likely too wet to work.
Even without soil compaction, tobacco does not develop as extensive
of a root system in a wet year as it does in a dry year, particularly
with a wet early season when roots develop the most. In a wet season
where water is readily available, the plant is not forced to develop a
larger root system to search for water. The result is a crop with a
relatively shallow root system that is more prone to lodging in wind
later in the season, and also susceptible to showing a multitude of
nutrient deficiencies, even when ample nutrients are available. As the
plant grows, the limited root system physically cannot keep up with the
rapid top growth of the plant. Potassium deficiency is most common under
these conditions, but phosphorus deficiency symptoms may also occur
(see images). During a wet season like 2013, tobacco may even appear to
be showing nitrogen deficiency symptoms of yellowing from the bottom of
the plant upward. The first reaction of growers seeing these symptoms is
to add more nitrogen or more of whatever nutrient appears to be
limiting. Most often the deficiency is temporary and the crop recovers
over time without additional fertilizer, or the root system is so small
that no amount of additional fertilizer would cause significant
recovery. In Kentucky, nitrogen losses should be minimal even in wet
seasons when tobacco is grown on soils that are well drained but not too
sandy. Adding additional nitrogen, particularly after layby at 5 weeks
or so after transplanting can be more detrimental to the crop than any
nitrogen deficiency symptoms, resulting in rank growth later in the
season, increased potential for green cured leaf, and possible increases
tobacco-specific nitrosamines (TSNA).
Temporary potassium deficiency from poor root growth
Temporary potassium deficiency from poor root growth
Temporary phosphorus deficiency from poor root growth
Water damaged tobacco compounded by black shank.
Although some crops got severely injured from single large rain
events of 6 inches or more during 2013, causing tobacco to wilt due to
saturated soil conditions and later sunscald, damage this severe was
localized in certain areas and many crops showed substantial recovery
when injury occurred early in the season. The most common results of the
wet 2013 season were yields that were substantially lower than
expected. The ultimate effect of a wet season on tobacco is thin leaf
from plants that may look good and feel heavy at harvest, but weigh
several hundred pounds per acre less than expected when cured.∆
DR. ANDY BAILEY: Extension Tobacco Specialist, University of Kentucky