Protection Methods

- During cultivation
 
There is no control method to control Verticillium wilt during cultivation. No fungicides are currently registered for this disease on tobacco. Treatment with fungicides belonging to the carbamic acid derivatives and benzimidazoles, recommended on other cultures, cannot be applied to tobacco. Given the late onset of the disease, the cost of such treatments would be too high and their effectiveness relatively low. 
 
At the end of the growing season, it is quite common to bury crop residues into soil. Buried plant tissues are abundantly colonised by Verticillium dahliae which produces numerous microsclerotia. The removal of plants limits this phenomenon and helps to reduce the amount of inoculum left in fields.
 
 
- Next crop 

The tools used in contaminated fields should be carefully cleaned before their use in other healthy fields. The rule is the same for the tractor wheels. A thorough rinse with water and disinfection of such equipment is often enough to get rid of the soil and Verticillium dahliae.
 
Crop rotation prevents or delays the occurrence of the disease. To be effective rotations should be long enough and must not involve susceptible crops such as tomato, egg-plant, potato, or cotton (figure 1). Control of weeds (figure 2), for example black nightshade and pigweed, should be taken into account. The monocotyledons, including cereals do not seem to be affected by this vascular fungus.
 
Occasionally disinfection of nurseries with a soil fumigant such as chloropicrin is done to control the disease. This measure is rarely applied in open fields. Its use is questionable considering its cost and relative effectiveness. Solar disinfection of the soil (solarization), advised to control other soil fungi such as Thanatephorus cucumeris and Thielaviopsis basicola  reduces the incidence of Verticillium dahliae on cotton. It may be efficient also on tobacco. Flooding of contaminated plots helps to limit the number of microsclerotia in the soil, reducing the amount of available oxygen and increasing the amount of CO2. This measure does not seem to be enough to change the incidence of the disease that requires only a few propagules to develop in the plant.
 
The most effective solution is to use resistant varieties. Varietal differences of susceptibility to Verticillium wilt have been observed in Nicotiana. The variety Waimea of New Zealand has  partial resistance of probably polygenic nature. Lines V-1 and V-3, from the same country, have shown high resistance to a race 1 "tomato" of Verticillium dahliae occuring on burley tobacco in Chile. The nature of this resistance does not seem to be known. No other species of Nicotiana appear to be resistant to this fungus.

*In order to give a "universal" character for the proposed protection methods, we have produced a fairly comprehensive inventory of these and have included  the fungicides reported in the various tobacco producing countries. For some diseases, we have even suggested alternative phytosanitary methods. It is obvious that the adaptation of these recommendations varies depending on the country and the pesticide legislation prevailing in the given country.