North Carolina Plant Disease and Insect Clinic
Plant Disease Fact Sheets

Disease Management in Tobacco Greenhouses

Mina Mila, Tobacco Specialist

 

The most common diseases observed in tobacco greenhouses in North Carolina are Rhizoctonia stem rot or damping off, Rhizoctonia target spot, Pythium root rot, and Sclerotinia collar rot. Some other diseases observed in lower frequency are bacterial soft rot, black root rot, blue mold, and Botrytis gray mold.


1. Sanitation - All precautions should be taken to ensure that field soil or used media does not enter greenhouses.


- Polystyrene trays should be sanitized using 3 lb/1000 cu ft. methyl bromide for 24 hours and allowed to air dry for 48 hours. Considerations for using methyl bromide: Crisscross trays up to a 5 feet high, tarp and sealed on concrete or on a tarp, then fumigate. Check that the air temperature is above 65 F at the time of the fumigation


Do not fumigate inside the greenhouse. Steaming trays at 176 F for about 1 hour is equally effective as use of methyl bromide.


If seedlings are infected with Tobacco Mosaic Virus trays should be disposed; the virus will remain active even after tray sanitation.

- Never dump old trays, old media, infected plants, and clippings around greenhouses. 

2. Solarization - Solarization is using the heat from the sun to kill plant pathogens in the greenhouse during periods when plants are not present. Solarization is very effective in controlling many pathogens but may have the disadvantage of damaging certain components within the greenhouse structure, including PVC pipe and polystyrene trays. For proper solarization, heat sensitive items should be removed and the gravel should be moist. All doors and vents should be closed during July or August for a period of at least 7 days (bright, sunny), 8 hours a day, to allow temperatures to reach 140 F. Another form of solarization is practiced when at the end of the transplant growing season, the black plastic or black ground cloth is left on the ground. This helps to prevent weed growth and keeps soil temperatures high enough to kill disease causing organisms close to the soil surface. Solarization will kill most of the disease-causing bacteria, fungi, and nematodes down to about 1/2 inch in the soil. 

Diseases that affect tobacco in greenhouses