In the U.S., burley tobacco plants are started from pelletized seeds placed in
polystyrene trays floated on a bed of fertilized water in March or April. Transplanting begins in May and progresses through June with a small percentage set in July. Producers must contend with major diseases, such as
black shank and
blue mold, and insects including
aphids,
tobacco hornworms, and
budworms. Plants are topped by removing the developing flower head roughly 60 days from transplanting, and treated to prevent the growth of side shoots called
suckers. Topping allows energy that would have produced a bloom to promote leaf expansion. Many of the benefits in topping at the appropriate bloom stage and
leaf number are lost if suckers are not controlled. Suckers grow vigorously immediately after topping and can severely reduce yield and quality if not effectively controlled. Some varieties, such as 'KY 14xL8' and 'Narrowleaf Madole', are known to have more rapid sucker growth than other varieties and may require more aggressive sucker-control strategies. Three types of
chemicals are available for controlling sucker growth on tobacco. About four weeks after topping, the tobacco is stalk-cut, using a knife that is shaped like a
tomahawk. Each plant is speared, spiked, or spudded (the terminology depending on the geographic location) onto a stick topped by a metal spear, spike, or spud that fits over the stick. Each stick contains five or six stalks. Sticks of green-cut tobacco are most often allowed to field-wilt for three or four days prior to hanging in a barn. Tobacco is allowed to air-cure for eight or more weeks, turning from the normal pale green to yellow and then to brown. Burley that cures too quickly can retain some of the yellow pigments, as well as chemicals that normally break down with a slower cure. The quality achieved by U.S. burley producers is primarily due to natural curing conditions. Once fully cured burley is taken down, sticks are removed and leaves are stripped from the plant into grades by stalk position. Leaves are baled by grade and taken to a receiving station run by a tobacco manufacturer or leaf dealer. ==Sweetening==