Protection methods

•  During cultivation 

There is currently no curative control method that can control viral infections in the field. A plant infected with the zucchini ( yellow mosaic virus Zucchini yellow mosaic virus , ZYMV) will therefore remain so throughout its life.

At the very beginning of an epidemic, it can be useful to eliminate the first infected plants , particularly in cultivation under cover. However, be aware that viral symptoms are expressed only 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 to plants of culture. Unfortunately, they are generally not effective in preventing the development of ZYMV epidemics, as the vectors often come from outside the field, and transmit the virus in very brief bites before the aphicide has even reached. time to act. Sometimes we even observe a hyper-activity aphids on the treated plots, which can lead to an even faster development of viral epidemics.

• Next crops

Certain prophylactic practices can limit or delay the development of ZYMV outbreaks:

- weed carefully the plots and their surroundings (edges of hedges, paths, surroundings of shelters, etc.) in order to eliminate potential sources of viruses and / or vectors;
- mulch the crops with plastic films (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 blanket is not completely waterproof. 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 space well the farm and avoid planting crops intended for late production near earlier crops which risk being already contaminated.

To control ZYMV epidemics, it can be considered to use a biological control method: premunition ^* . Indeed, an attenuated strain of ZYMV has been isolated: it does not affect the yield and effectively protects all cucurbits against infections by most of the severe strains of this virus. The use of this method of protection is authorized in Europe. If it were to become commercially available again, it could be applied profitably to crops at risk, particularly in the off-season.

The easiest control method for growers to use is still resistant varieties ZYMV , when possible. There is currently no commercial variety of melon resistant to ZYMV. A gene for resistance to this virus has been identified in an Indian variety, but it is unfortunately very easily bypassed ^** . Therefore, breeders have been advised not to use it, pending the discovery of other resistance genes.
 

^* The premunity is a special property to plant viruses. Thus, if a plant is infected with a strain of a given virus, it cannot be subsequently infected with another strain of the same virus.
** Resistance is bypassed if a strain of virus can cause strong symptoms in a variety possessing that resistance.