Protection methods

• During cultivation

No method of struggle is curative; a plant infected by the cucumber mosaic virus ( Cucumber mosaic virus , CMV) will remain all his life. At the very beginning of an attack, it can be useful to eliminate the first infected plants, especially in cultivation under cover. However, be aware that symptoms do not appear until after an incubation period of one to two weeks, during which time the plant can be a source of virus for aphids. Therefore, when the first symptoms are observed on the first plants, the epidemic may already be developing.

The insecticides are useful to reduce aphid populations, if they are important in the culture. Unfortunately, they are generally not effective in preventing the development of CMV epidemics, as the vectors often come from outside the field, and transmit the virus in very brief bites even before the aphicide has had an effect. time to act. Sometimes aphid 'hyper-activity' is even observed on the treated plots, which can lead to an even faster development of viral epidemics.

• Next crops

Certain practices can limit or delay the development of CMV epidemics:
- weed carefully the plots and their surroundings (edges of hedges, paths, approaches to shelters, etc.) in order to eliminate sources of viruses and / or vectors;
- mulch the crops with films  plastic (transparent or thermal opaque) which repel aphids. This practice is mainly intended for field crops and can delay epidemics by 2 to 3 weeks, until the foliage covers the mulch, then annihilating its repellent effect for aphids.
- protect nurseries and young plants in the field with non-woven sails (Agryl P17 type) or mesh fabrics (Filbio type). Unfortunately, this type of protection must be removed - at least partially - at flowering, so as not to prevent the action of pollinating insects essential for fruit production. The young shoots thus discovered can then be quickly contaminated by aphids. The use of small perforated plastic caterpillars (type 500 holes / m ² ) is also an effective means of delaying viral epidemics which does not present the constraint of uncorking at flowering, since pollinators can penetrate under the caterpillars. However, this type of cover is not perfectly 'impervious' to aphids and care must be taken to avoid the establishment of colonies of the melon aphid, A. gossypii , which under these shelters find particularly favorable conditions for their proliferation.
- manage the farm space well and avoid planting crops intended for late production near earlier crops which risk being already contaminated.

The easiest control method for producers to use is still resistant varieties .

In melons, research is underway in many countries to identify resistance to CMV. For the moment, only partial resistance (also known as intermediate resistance) has been identified in genetic resources. Breeding programs are underway to try to introduce them into commercial varieties, some of which are already less susceptible to the virus.

- In zucchini : there are quite a few commercial varieties with good levels of resistance to CMV in the field. Commercial transgenic varieties (GMOs) expressing the capsid protein ^* of the virus exhibit a very high level of resistance. They provide very good protection against CMV, but can only be used in countries where the legislation allows the cultivation of this type of variety (USA, for example).
- In cucumber : there is high level resistance to CMV in the main varietal types.
 

^* The protein capsid is a protein which protects the nucleic acid and which therefore is the main constituent of the viral particle.