Potassium Deficiency/Target Spot

KdeficiencyPotassium Deficiency

In select tobacco fields, potassium deficiency has started to develop.  Potassium deficiency is characterized by burning of the leaf tips and margins on mid-stalk leaves (primarily cutters).  This deficiency is most common on deep, sandy soils that have low nutrient holding capacity.  It is common to see potassium deficiency under extreme weather conditions since potassium must be in soil solution for adequate uptake.  Soil moisture must be adequate, neither too dry nor too wet, for plant uptake of potassium.  If too dry, water is limited in soil, therefore; potassium movement through soil to the root zone becomes limited.  If too wet, leaching below the rooting zone becomes a concern.  In addition, potassium deficiency can occur during periods of rapid plant growth (layby to topping) since tobacco demands high amounts of potassium for growth and development.  With improved soil conditions and additional root growth into new areas of the soil, the deficiency should be corrected.  Additional potassium should be applied if a soil test indicates low levels of potassium.  Depth sampling will help quantify the amount and location of potassium in the soil profile.

Target Spot

TargetSpot1Target spot is beginning to show up in locations throughout Wayne County and Eastern North Carolina.  Symptoms of target spot are well known amongst tobacco growers.  Lesions appear on lower leaves as small, brown spots with concentric rings and a chlorotic (yellow) halo around the perimeter.  Overtime, the leaf tissue will become necrotic and leave a “shot-hole” appearance.  Whenever you have extended periods of leaf wetness with poor air circulation, a favorable environment for target spot development has occurred.

Quadris is labeled for control of target spot.  When applying Quadris, remember that plant coverage is critical in order to control target spot lesions.  Labeled rate for Quadris on tobacco is 6oz-12oz (most use 8oz-9oz).  Use plenty of water (around 25 gal/ac) to achieve optimum coverage.  If coverage becomes an issue, consider using drop nozzles to effectively get material to target site.

***DO NOT CONFUSE TARGET SPOT WITH WEATHER FLECK!  The main difference between the two is that target spot has concentric rings and weather fleck does not.  Most of the time, weather fleck develops as brown spots but becomes white over time.  There is no control measure for weather fleck since it is a result of air pollutants (ozone).

Recommendations for the use of chemicals are included in this article as a convenience to the reader.  The use of brand names and any mention or listing of commercial products or services does not imply endorsement by the North Carolina Cooperative Extension Service nor discriminated against similar products or services not mentioned.  Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label.  Be sure to obtain current information about usage and examine a current product label before applying any chemical.  For assistance, contact your county’s North Carolina Cooperative Extension  Service.