Protection methods

• During cultivation

No curative control method is available; a plant infected with melon ( virus Melon necrotic spot virus, blight MNSV) will remain so throughout its life, although sometimes symptoms may improve. We can observe differences in sensitivity depending on environmental conditions. The periods of the year with reduced temperature and light seem more favorable to the expression of the disease. At the very beginning of an attack, it can be useful to eliminate the first infected plants, particularly in soil-less culture. However, as the symptoms did not appear until a few days after contamination, the plant may have already been a source of virus for the fungus vector. Also, if the source of inoculum is the substrate or the soil, this practice will have no effect.

The treatments against the vector fungus, especially in soilless culture, can be very useful to limit the spread of the disease. The addition of Agral® at 20 mg / l in the nutrient solution has been shown to be effective in destroying zoospores and therefore preventing the spread of the virus in cucumber cultures on rock wool, in Great Britain and Holland.

The disinfecting tools size (trisodium phosphate, bleach) reduce the possibility of mechanical transmission of the virus.

• Next crops

Certain cultural practices are likely to effectively limit the development of the disease:
- if possible, disinfect the soil or substrates (with the techniques and active materials authorized by the regulations in force) before setting up a sensitive crop, particularly if attacks have been observed in previous years;
- carry out rotations regular crop ;
- avoid the reuse of rock wool cakes that have borne diseased plants, or disinfect them carefully beforehand;
- use Agral® in nutrient solutions;
- use grafting on resistant plants such as certain squash ( Cucurbita fïcifolia );
- disinfect cutting tools with 10% trisodium phosphate.

A recessive resistance MNSV gene has been demonstrated in melon and several commercial varieties possessing this resistance are available on the market, in particular in the Galia type.

A strain of MNSV bypassing * this resistance has been reported once in southern Spain, but fortunately this strain has not been observed in other production areas. Another resistance mechanism preventing virus migration into the plant has been described, but it has not yet been introduced into commercial varieties.

No resistance has yet been reported in cucumber.

^* Resistance is bypassed if a strain of virus can cause strong symptoms in a variety with that resistance.