Factors Affecting the Population of Ralstonia Solanacearum in a Naturally Infested Field Planted to Tobacco

In 1996, tobacco generated US$700 million in Zimbabwe, which accounted for over 25% of the Zimbabwe’s foreign exchange earnings. Bacterial wilt was recorded in Zimbabwe as early as 1926 (Eyles, 1926) but it has been confined to the Mvurwi/Concession tobacco growing district since the 1980’s. It was reported for the first time in 1997 in Burma Valley district (fig. 1). Infections in fields are usually very mild with losses of less than 5%, but since the disease is soil-borne, its destructive potential is unpredictable. During the 1880’s the tobacco industry in Granville county, North Carolina was destroyed by bacterial wilt. Even today, annual losses of 1.5 % to bacterial wilt are not uncommon in North Carolina (see Fortnum and Martin, this volume).