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Protection methods

In France, the Tomato spotted wilt virus (TSWV) is classified in the list of mandatory quarantine pests.

- During cultivation

There is no curative control method that can effectively control TSWV during cultivation. An infected plant will remain so for its entire life.

If attacks take place in the nursery and are detected early, the few plants showing symptoms of TSWV will be quickly destroyed and never planted subsequently.

The insecticide treatments are essential to control thrips populations on salads. A number of products can be used both at ground level and above ground. In France, the number of usable products is very limited, if not zero. Some aphicides have side effects against these insects. Generally, the treatments are ineffective in controlling epidemics of this virus, especially in the open field. 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. Strains of Frankliniella occidentalis resistant to several insecticides (dimethoate, acephate, oxamyl, fenpropathrin) are reported; they do not help to improve the effectiveness of chemical control against these insects. They should make us aware of the value of alternating insecticides with different modes of action. To be effective, the treatments must be carried out early, ensuring good penetration of the mixture, so as to reach the places where the thrips take refuge.

At the end of the culture, we will eliminate all diseased plants . We can also advise to leave the plot empty for 3 to 4 weeks so that the larval stages still present on the ground and the plant debris evolve and that the thrips disperse elsewhere thereafter. Under shelter, we can also create a crawl space of a comparable duration. In some cases, soil fumigation is recommended. The shelters can also be disinfected.

- Next crop

In countries where contamination is very early, it will be necessary to try to prevent or limit contamination as much as possible. For this, we can:
- destroy weeds and nymphs on the ground. Disinfection of the latter may be considered;
- protect young plants by using agrotextiles (non-woven sails, mesh fabrics, etc.). The mechanical barrier thus created will delay contamination. The plants put in place must be healthy;
- 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 carried out carefully in the open field.

It will also be desirable to integrate production, step by step, sensitive to vectors, into the rotations . It will also be necessary to avoid setting up a nursery or a salad crop near a crop sensitive to this virus and its vectors (especially ornamental species: anemones, chrysanthemums, buttercups). As with aphids, ground cover with aluminized plastic film has been shown to reduce the number of thrips present in salad plots, as well as the incidence of this virus.

The insecticide treatments will be needed to reduce thrips populations.

A model to predict the incidence of this virus has been developed in Hawaii. It has shown that the initial frequency of diseased plants in the crop better reflects the risk of crop damage, compared to the abundance of thrips. For this reason, it will be beneficial to eliminate the very first sick salads.

It should be noted that a number of descendants of an interspecific cross between Lactuca sativa and Lactuca saligna have been shown to be resistant to a Hawaiian strain of TSWV. In addition, two partially resistant cultivars , Tinto and Ancora, would have the same genes of lower sensitivity; this resistance would be partially dominant.
On the other hand, genotypes of the wild species L. perennis , incompatible with lettuce, have been identified as resistant.

NB: Controlling insect populations on a crop implies, depending on the situation, the use of insecticides. As the number of insecticides available for a given use is constantly changing, we advise you to consult the e-phy site of the Ministry of Agriculture and Fisheries which is an online catalog of plant protection products and their uses, materials. fertilizers and growing media approved in France. This also applies to all biological products based on microorganisms or natural substances.

Last change : 04/27/21