When the nurseries are established at the same greenhouse each year, it is essential to provide a "sanitation break" (i.e. absence of any plant material during a certain period) between two plant productions cycles. During this period, the surfaces of shelters, structures, equipment such as trays, tools, plant tables, pots, boxes, must be disinfected to destroy spores and propagules of pathogens. Several products are typically recommended for use in greenhouses:
- Bleach (sodium hypochlorite at 48 ° Chl.), 0.3-0.5% for above groundsurfaces , 4-7% for structures;
- if you choose a specific disinfectant, ask help from a technician and please refer to legislation prevailing in your country.
 

For most of these applications, a thorough rinse with clean water is essential. Rinse using high pressure and plenty of water on surfaces and structures of shelters. 
 

During disinfection, the usual precautions should be taken such as use of gloves and masks as the products have some level of toxicity (by contact and vapour) and are corrosive.

 
 

The soil should be disinfected with a fumigant such as dazomet, if tobacco seeds are sown in the soil or plants produced in clods placed on it. In the latter case, the frequency of disinfection should be larger and you should isolate the clods of soil with plastic film. This film should be replaced annually or when it tears. In the case of floating seedbed system, the trays must be disinfected. Trays and tarps must be changed annually if possible. Some suppliers of polystyrene trays are now committed to take them back after one has used them and recycle them. They can also be disinfected and the vapour seems to work best. One should note that the soilless cultures are as or more vulnerable to outbreaks of soil-borne pathogens as the other systems of production. It is therefore essential to cover the soil with a plastic film to avoid contamination by soil particles (figure 1). 

 

Between two nurseries, special attention should be given to the storage of new materials used in plant production such as polystyrene trays, plastic alveolus, substrates in bulks or in bags, or even disinfected and reused equipment. If they are improperly stored, in a dusty and / or windy place, contamination by soil dust is possible. For instance torn substrate bags or polystyrene trays can be contaminated with Thielaviopsis basicola.

 
 

Avoid using the same shelters to produce other plant species, because, if they are hosts, they can multiply pathogens affecting also tobacco such as PVY, and Rhizoctonia solani. It is also advisable to remove all weeds around nurseries so that pests (predators or direct virus vectors) cannot harbor in them and then enter the interior of the shelter and infect tobacco plants (figure 2 ).

 

*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.

 

Last change : 04/19/13

• Author :
• D Blancard (INRAe)