Protection methods

• During cultivation

There is no curative control method that can effectively control the tomato ( spotted wilt virus Tomato spotted wilt virus , TSWV) during cultivation: an infected plant will remain so throughout its life.

Note that several regulatory provisions have been adopted to limit the spread of TSWV. In France, the measures put in place by the Ministry of Agriculture in 1990 had two objectives: to limit the introduction of TSWV by imported plant material (inclusion on the list of quarantine pests) on the one hand and, on the other on the other hand, prevent the spread of the virus when it is present (classification as a compulsory control parasite). Sampling and testing campaigns carried out by the Plant Protection Service have revealed “risk channels” and have had a real deterrent effect. In 1992, a European directive confirmed TSWV as a quarantine and compulsory control pest. The application of the national decrees implementing this directive required the development of detection methods, and the Elisa technique was chosen.

If attacks take place in the nursery and are detected early, the few plants showing symptoms of TSWV will be quickly destroyed, never planted subsequently. Blue traps will be set up in order to follow the evolution of the thrips populations, and thus to control them more clearly.

The insecticide treatments * may be needed to control thrips populations on tomato, and thus reduce the incidence of TSWV. A certain number of products, especially organohalogenated insecticides or carbamates, can be used in this regard, both at ground level and on the aerial parts: abamectin, deltamethrin, acrinathrin, spinozad ( e-Phy ).

The reported strategy is to treat the plants 3 times, 4 to 5 days apart, alternating the chemical families and ensuring good penetration of the mixture so as to reach the places where the thrips take refuge. Applications will be made in the early morning or late afternoon when thrips are very active. Soil treatments can control the pronymph and nymph stages which often burrow into the soil.

It should be remembered that insecticide treatments are generally not very effective in controlling epidemics of this virus, especially in open fields. In fact, vector thrips often come from outside the plot and transmit the virus during their nutrition, even before the insecticide has time to act.

At the end of the culture, we will eliminate all diseased plants . We can also advise to leave the plot without culture for 3 to 4 weeks, this so that the larval stages still present on the ground and the plant debris evolve, and that the thrips disperse elsewhere thereafter. The shelters will be disinfected , and we can create a crawl space of a comparable duration. In some cases, fumigation soil is recommended.

• Next crop

Particular attention should be paid to the quality of the plants in the nursery, which may be infected early. In fact, it has been observed that low levels of contamination at this stage of the crop have a strong impact on the development of epidemics in the field. Therefore, efforts will be made to prevent or limit contamination as much as possible, a fortiori in countries where they are very early in the nursery. For this, we can:
- destroy weeds and nymphs on the ground. As such, disinfection of the latter may be considered;
- produce the plants in an greenhouse insect proof or protect them by using agrotextiles (non-woven sails, mesh fabrics?). The mechanical barrier thus created will delay contamination;
- weeding the surroundings of the nursery in order to eliminate the sources of viruses and / or vectors. This measure is particularly important in the case of this virus. It will also be carefully carried out in the open field;
- ensure that the plants put in place are healthy .

It will also be desirable to integrate the rotations productions with little or no vector sensitivity into . We should also avoid setting up a nursery or a tomato crop near a crop sensitive to this virus and its vectors (especially ornamental species: anemone, chrysanthemum, ranunculus ). As with aphids, it has been shown that plastic or aluminum films applied to the ground made it possible to keep thrips away, and thus to reduce the incidence of TSWV on tomatoes. In addition, corn hedges around the plots have been shown to be effective in reducing the incidence of TSWV outbreaks in Brazil.

Let us add to the recommendations for preventive insecticide treatments * detailed previously ( e-Phy ) that various oils and products forming films on the surface of plants would modify the diet and reproduction of F. occidentalis , and therefore reduce TSWV infections.

Several auxiliaries are used in glasshouses to biologically control thrips, in particular various predators and parasites: the mites Amblyseius cucumeris and A. barkeri (Phytoseiides), bugs hemiptera of the genus Orius (Anthocorides) and other bugs, especially in the family of Mirides, such as Dicyphus tamaninii .

Different species of Lycopersicon have been evaluated for resistance to TSWV in Hawaii, France and the United States. Among them, L. peruvianum has a very high level of resistance controlled by the dominant gene " Sw-5 ". This causes a hypersensitivity reaction to most TSWV isolates. Thus, the number of hybrids resistant to TSWV on the market is currently increasing in different crop types. However, it should be noted that various symptoms, in particular systemic, have been observed occasionally in Spain on resistant plants. Several highly competitive strains of the virus isolated from these plants have been shown to be able to overcome the " gene Sw-5 " . On the other hand, they do not seem able to attack the lines of L. peruvianum ('PI 128 660 R', 'PI 128 660 S'), on which they produce local lesions without systemic infection. Such strains of TSWV have appeared in South Africa and Australia. It is probable that the attacks observed sometimes in the field, especially in Spain, are due to the incomplete dominance of " Sw-5 ". The hybrids on the market are probably all heterozygous for this gene.

It should also be known that the “ gene would Sw-5 ” also confer resistance to Groundnut ringspot virus (GRSV) and Tomato chlorotic spot virus (TCSV).

Two INRA populations were improved and disseminated to breeding establishments, after two generations of diversifying and improving crosses of an initial line close to the types cultivated in France in the open field. They accumulate genes for resistance to various diseases, one more in greenhouses and the other more in open fields.

Finally, we report resistance to TSWV transmission by thrips in Lycopersicon hirsutum f. glabratum , as well as in the cultivars L. esculentum 'Manzana', 'Brazil' and 'Anahu'.

Several strategies transgenosis , for example based on genes encoding the nucleocapsid or the NSm protein (putative movement protein), have been shown to be effective against TSWV. No tomato genotype currently on the market uses one of these potential resistances.


* 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.