Like many bacterial diseases in plants, speckling is very difficult to control . Its control will require the harmonious implementation of all the measures recommended thereafter.

• During cultivation

When the first spots are observed in a tomato plot, it is unfortunately too late to intervene effectively: we do not have very effective measures to prevent the development of this disease.

The copper * in the form of salts can be employed to limit the extension of this bacterial copper, copper sulfate, copper copper hydroxide, copper cuprous oxide, copper oxychloride, copper ( e -phy ). It only has a preventive effect on the surface of the aerial organs. Acibenzolar-S-methyl can now be used in France to control this bacteriosis, as in other countries.

It should be noted that the intensive use of copper (which is not degraded in the soil and accumulates there) led, during the 1980s, to the appearance of strains more or less resistant to the salts of this metal, in especially on the American continent. In addition, as for copper, strains resistant to streptomycin appeared during the 1960s. Finally, it should be noted that in a good number of situations, these treatments are not sufficient to prevent the epidemics of speckling when the climatic conditions. are favorable.

In addition to copper treatments, we can also recommend reducing sprinkling irrigations to their strict minimum and carrying them out during the day, at a time when the plants will quickly emerge. In addition, it is advisable to work and circulate in the crops only when the plants are dry. Good crop ventilation will reduce the duration of foliage wetting and therefore prevent infections and lower the impact of the disease.

During harvest and at the end of cultivation, avoid leaving plant debris on the ground or burying them . If you can not do otherwise, the burial will be deep in order to activate their decomposition.

• Next crop

In the nursery
It will be essential to use seeds of irreproachable sanitary quality. In case of doubt, their treatment will be necessary. Several methods or means of disinfection make it possible to eliminate more or less well the bacterial cells present on the seeds:
- hot, dry air (70 ° C for 96 hours, which seems to slow down the speed of seed germination);
- water at 50 ° C for 25 minutes;
- fermentation of the pulp and seeds for 4 to 5 days;
- soaking the seeds in a 0.8% acetic acid solution for 24 hours, or in 5% hydrochloric acid for 5 to 10 hours, or in 1.05% sodium hypochlorite for 20 to 40 minutes or in 0.05% mercury chloride for 5 min.

These different methods are effective especially on external contamination of seeds.

The soils of nurseries will be disinfected with steam or using a fumigant. It will be the same for the structures and the walls of the shelters. Note that solarization would reduce the bacterial populations of P. syringae pv. tomato up to 30 cm deep in nursery soils, significantly limiting the incidence and to a lesser extent, the severity of the disease.

The production of plants in clods will be preferable; it will be carried out in healthy substrates and in various supports placed on shelves, in no case in contact with the ground. Sprinkler irrigation will be limited or organized in such a way as to obtain rapid drying out of the plants; these should be avoided when they are still wet. Tools will be disinfected, and workers will wash their hands before and after handling plants. One should be wary of introducing plants of dubious origin into the farm. You should be aware that the plants received may be apparently healthy, but harbor the bacteria that will be expressed later.

Some treatments * based on copper or acibenzolar-s-methyl ( e-phy ) will be performed several times in the nursery, in order to ensure the production of healthy plants. These can be the cause of the introduction of bacteriosis in the culture. The frequency of treatments will vary depending on the production area and the risks involved. For example, some technicians recommend copper treatments starting 5 days after emergence and continuing every 4 to 5 days. Disease-free plants should be purchased, preferably having been produced in semi-arid areas that are not susceptible to this bacterial blight. In some countries, plants can be certified free from this bacteriosis.

At the field
The rotations of 2 to 3 years will be carried out with non-host plants - especially cereals - which are many because the parasite selectivity of this bacterium. Weeds will have to be eliminated, because a certain number of them allow its multiplication and its maintenance in the plots. One should also beware of spontaneous tomato seedlings in plots where sheaths have been preserved.

The fertilization must be balanced , in no case too weak or excessive, because these two situations seem to favorably influence the speckling. Line or localized irrigations are preferred to those by sprinkling.

They avoid planting too early in the year , so as not to expose plants to low temperatures and wet. The proximity of pepper crops or another tomato plot, especially if they are already infected, should be avoided.

The application of products based on copper or Acibenzolar-s-methyl ( e-phy ) will delay the development and spread of this bacteriosis. Spraying should take place after planting and during the season. It will be best to treat the plants when they are dry and just before rains are expected. In California, applications are made before each rain and at a frequency of 10 to 12 days when weather conditions are cold and wet. They are stopped when temperatures reach 32 ° C. In France, the treatments against this bacteriosis are rather carried out in May and June.

A source of resistance has been described in the wild species Lycopersicon pimpinellifolium and in various cultivars in the form of an incompletely dominant gene, " Pto ". Homozygous genotypes often reveal a better level of resistance to this bacteriosis. Note that the expression of this resistance is closely associated with another locus, " Fen ", which confers sensitivity to an insecticide of the organophosphate family: fenthion. Phytotoxicity is expressed by the appearance of spots on leaflets similar to those caused by the bacteria. This situation facilitates the work of breeders who can use this insecticide to screen their collections and improve their plant material. A number of cultivars for field tomato crops exhibit this resistance. Other wild species would be resistant to this bacterium ( Lycopsersicon glandulosum, L. hirsutum and L. peruvianum ) and other sources of resistance would exist.

Note that a strain capable of developing on several cultivars resistant to speckling was reported in California in 1998 and identified as race 1 of P. syringae pv. tomato . This race 1 was also demonstrated in Italy in 1995 on a resistant cultivar heterozygous for the “ gene Pto ” . Its virulence was confirmed on the variety 'Ontario 7710' which is homozygous for this gene and has a high level of resistance.

Several antagonistic microorganisms , natural defense stimulators and various products have been tested with varying degrees of success with regard to aerial bacteriosis of tomatoes, speckling, but also bacterial scab. We report a number of them here in order to make them known to you and, for some, to use them if their use is already authorized in your country.

The micro-organisms that can be mentioned are almost exclusively other bacteria : Pseudomonas putida, P. syringae Cit7, Rahnella aquatilis, Cellulomonas turbata , a non-pathogenic strain of Xanthomonas vesicatoria …

In addition, foliar applications based on bacteriophages have also revealed a certain effectiveness with regard to speckling, especially if they were carried out during the evening. Problems with the persistence of bacteriophages on the foliage were, however, noted, due to spraying but also to the presence of certain pesticides.

Several rhizobacteria that stimulate plant growth (PGPR) such as Pseudomonas fluorescens (associated with an antagonist bacterium Pseudomonas syringae ) or Azospirullum brasilense (in inoculation of seeds and in combination with foliar treatments based on copper in particular) have made it possible to reduce the attacks of this bacteriosis. The same is true for stimulators of the natural defenses * of plants (SDN) such as acibenzolar-S-methyl ( e-phy ). This compound would reduce the number of symptoms present on the leaves, but also on the fruits. Note that it is also successfully associated in the United States with treatments based on bacteriophages previously reported or the copper + mancozeb combination.

Finally, a product combining hydrogen peroxide, acetic acid and iron ion would limit the level of bacterial populations present on plants. Certain composts, used in aqueous solutions and sprayed on plants, are said to limit the severity of the disease. The same would to oil apply Azadirachta indica , fish-based emulsions, ammonium lignosulphonate and potassium phosphate.


* Chemical control : As the number of pesticides available for a given use is constantly changing, we advise you to always confirm your choice by consulting the e-phy site of the Ministry of Agriculture and Fisheries which is an online catalog of plant protection products and their uses, fertilizers and growing media approved in France. This also applies to all biological products based on microorganisms or natural substances.