Protection Methods

- During cultivation
 
No method is really effective during cultivation to protect plants from damage caused by different species of Meloidogyne. We can still advise to ridge up the plants in order to favour further rooting.
 
If the outbreaks occur in nurseries, the affected plants should be removed. Otherwise, if they are transplanted they will contribute to the spread of nematodes and contaminate the healthy soil.
 
At the end of the season, one must destroy and remove the root systems of tobacco from the field, to reduce the risk of increasing the nematode population in the soil. When this is not possible, one can expose the root systems in the open air so that they dry up. Similarly, several successive tillages conducted during the summer will help to expose the nematodes to heat and kill them.
 
 
- Next crop (figures 1 and 2) 
 
In order to be effective, the root-knot nematode control should include, in a complementary manner, all the control methods mentioned above.
 
It is essential to produce healthy plants. The nursery must be disinfected if one has any suspicion about the quality of nursery soil. In many countries, this measure is implemented systematically. Several nematicides can be used. Their choice will depend on the legislation of a country and the financial resources available:

- Fumigants (1,3-dichloropropene and 1,3 D, or D-D-dichloropropane-dichloropropene, dazomet, metam sodium, methyl isothiocyanate) are often polyvalent and are not only nematicides but also fungicides, insecticides, and herbicides. They are generally more effective in well-drained and porous soils. They act directly on nematodes. These products are mainly used in a nursery. They are more effective than non-fumigants. 1,3-D and D-D have a low activity on weeds. Dazomet and metam sodium are not widely used. Some of these products are also applied in the field;

 - Non-fumigants (ethoprophos, fenamifos, thionazin, aldicarb, carbofuran and oxamyl) are more specific products to control nematodes and soil-borne insects. They act either directly on nematodes in the soil or through the plant during feeding. They often temporarily inhibit the development of nematodes, but they do not necessarily kill them. They are  less expensive than fumigants. They are mostly used in the field, but their effectiveness is lower than that of the previously mentioned products. They are either added in pre-planting or sprayed in the following weeks (this is the case for oxamyl and fenamiphos).
 
The use of these products has several disadvantages: they are toxic to humans and the environment, they are not specific and disrupt the biological balance, they are costly and sometimes require specific equipment.
 
In countries where sunlight is high, a solar disinfection ("solarization") may be considered, especially to clean nurseries at a lower cost. This technique involves covering the soil with a polyethylene film of 25 to 40 microns thick; the soil should first have been properly prepared and moistened. The polyethylene film must be kept in place at least one month during a very sunny period of the year. It increases soil temperature and promotes the activity of microbial antagonism, which helps to reduce the presence in the soil of many plant pathogenic micro-organisms including some nematodes.
 
The use of floating seedbed systems should eliminate contaminations in nurseries, provided that the trays are protected against contamination by dust.
 
In some countries, nematode control is done by flooding contaminated fields for 7 to 9 months. The flooding can be continuous or interrupted by periods of soil drying. Under these conditions, the soil is deprived of oxygen and accumulates toxic substances to nematodes, such as organic acids, and methane. This method is effective only if done in a warm period of the year. The method represents risks of spreading the nematodes.
 
The tools used for tillage in contaminated fields should be carefully cleaned before use in healthy fields. The same principle applies for the tractor wheels. A thorough rinse with water and disinfection of such equipment is often sufficient to remove the soil and and nematodes. In some countries, plowing and early planting on raised beds reduce the impact of nematodes.
 
Crop rotations are frequently advised to delay the onset of nematodes or limit their spread. They are not always easy to implement, especially for some polyphagous nematodes such as Meloidogyne spp. or Pratylenchus spp. because it is not always easy to find resistant crops suitable for rotation. To be effective, the rotation should lead to an absence of susceptible hosts on the field for at least four years. There are a number of "trap plants" for nematodes or "nematicide" (Tagetes spp.) which are not yet used in rotation with tobacco. Weeds must be perfectly controlled in fields that will be used in the future, as a number of them serve as hosts and allow the multiplication of nematodes. In some countries fallow is recommended, but it sometimes causes problems of soil erosion.
 
The fertilisation and irrigation of plants should be totally under control.
 
 

*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.