September 3, 2003

Kentucky’s burley harvest is under way and is being affected by less than optimal weather conditions.

Frequent rains can interrupt a timely harvest, reduce the opportunity for field wilt, increase the likelihood of having dirt splatter onto harvested tobacco in the field and cause high humidity curing problems both in the barn and in field curing structures, said George Duncan, a University of Kentucky agricultural engineer.

To help with curing when housing tobacco in a barn, space it on tier rails to prevent overlap of green tips on the dry flyings. This is done by staggering the sticks of tobacco on the tier rails or only hanging every other tier if barn space allows. For field structures, do not force the sticks of tobacco tightly against one another.  Space the sticks four to five inches apart this year with this big, green, moisture laden crop, Duncan said.

Regular attention to and management of the curing environment is important to provide the best possible conditions for ventilating and curing tobacco.

“Curing burley is not just drying the leaf,” Duncan said, “but a four-week to six-week process that allows chemical changes to occur as the leaf dries.”

Good burley curing in the barn or field structure requires daily average humidity of about 65 to 70 percent to sustain enough leaf moisture for the necessary chemical changes to produce the tan and brown leaf colors. Cool fall temperatures below 50 to 60 degrees are detrimental to good burley curing, he said.

Consecutive days of high or low humidity can also cause problems. Humidity above 80 percent for three consecutive days in a warm environment allows bacterial action to accelerate and cause rotting.  Low humidity – below 50 percent – for several days can desiccate the leaf moisture, stop chemical reactions and set undesirable green or yellow colors in the leaf.

During warm humid weather, when the tobacco is still green to yellow in color, Duncan suggests keeping the barn ventilator doors open daily and allow maximum air ventilation though the tobacco. Supplemental air movement using large fans can improve the airflow through the tobacco and increase moisture removal. Field structures need to have the plastic sides rolled up for cross ventilation.

If the weather turns dry for a week or longer and the tobacco does not become pliable each night, the barn ventilator doors need to be opened at night to all any nighttime moisture into the barn and closed early in the morning to contain as much moisture as possible in the barn during the hot, dry part of the day. The addition of moisture by misting nozzles or other humidification equipment can help, he said.

Field curing structures need the plastic on the windward side lowered, but need the other side open to allow any dew and moisture at night to infiltrate the leaf.

Remove and strip tobacco from field curing structures as soon as possible after curing is complete to prevent damage from fall winds and storms, Duncan said.

“There are various instruments available for $25 or more that can give reliable relative humidity readings when used and protected carefully,” he said. “Obtaining one of these may be the best investment you can make in knowing how to properly manage your tobacco curing environment.”

For more information, contact your local UK Cooperative Extension Service office or the biosystems and agricultural engineering department at the UK College of Agriculture.



Writer: Laura Skillman 270-365-7541 ext. 278
Source: George Duncan, 859-257-3000 ext. 115