• During cultivation

The control of Botrytis cinerea was and still is difficult in France (as in many countries of the world), especially in shelters. This situation has several explanations:
- a climate entirely favorable to the development of this fungus;
- particularly receptive plants , with more succulent and tender organs than in the open field and numerous wounds caused by pruning and disbudding;
A particular aptitude of this fungus to adapt quickly to fungicides which can be used for “ use Botrytis ” on tomatoes, and belonging to a number which is sometimes too limited to chemical families to carry out judicious alternations;
- few fungicides with different modes of action available (not yet approved, withdrawn from the market following recent European legislation on pesticides).

When you notice symptoms of B. cinerea in your crop and if a preventive treatment program has not been implemented, we recommend that you make an application with a registered fungicide *. Several active ingredients are used around the world and in France, alone or in combination, to control B. cinerea ( e-phy ).

Note that several families of fungicides are affected by resistance phenomena. The genetic variability of B. cinerea has enabled it to adapt to many fungicides that have been opposed to it. For example, dicarboximides , very efficient in the early days of their use, quickly led to the selection of resistant (non-persistent) strains which are now very common in many cultures. It should be noted that strains tolerant to fungicides of the family are still found in the field benzimidazole , used at one time against B. cinerea, . Unfortunately, a comparable situation has been observed with the intensive use of almost all of the most recent antibotrytis fungicides.

It is therefore strongly recommended to alternate the chemical families in order to avoid the appearance of resistant strains.

Note that treatments can be carried out following leaf stripping in order to protect pruning wounds. Thus, when a chancre forms at their level, the lesion can be cured in order to rid the stem of diseased tissues. A thick fungicidal spray will be applied, taking care to cover the wound well.

In addition, a set of should be put in place prophylactic measures complementary to chemical control , both in the nursery and in the field.

The shelters must be ventilated as much as possible , in order to reduce the ambient humidity and, in particular, to avoid the presence of free water on the plants. In a period of cloudy and humid weather, the ventilation and heating of the shelters will make it possible to manage the humidity well: gradually ensuring a temperature of around 17 ° C at sunrise will prevent condensation on the plants. Ventilation should however be used sparingly when the outside air is at a temperature below 12 ° C.

The size should be carefully : cut the axillary buds, leaves and stems of the bouquet at the grass stalks will maintain them the smoothest possible. Removing the axillary buds early will prevent large wounds. It should be kept in mind that the presence of more or less long snags greatly increases the risk of contamination. The pruning work will be done in the morning, because at this time, the fabrics, more turgid, are cut more easily; in addition, the wounds then have more time to dry out during the day. It will not be desirable to prune during cloudy and wet periods. Note that wounds on the stem, although dry in appearance, remain susceptible to B. cinerea for quite a long time.

Young cankers will be cured in order to eliminate the tissues colonized by this fungus. The wounds must be protected by a fungicide applied locally in the form of a whitewash or by means of generalized preventive treatments or directed on the lower part of the stem. Remember that leaf stripping from the lower part of the plants, in addition to making it easier to lay the plants down, promotes fruit ripening and simplifies picking, helps to improve the climate of the plant cover by improving air circulation in the crop. .

Under shelter, the irrigation will only take place when the plants will be able to evaporate. Water retention in the tomato results in plants that are more vegetative, with waterlogged and succulent tissues, and therefore more sensitive to B. cinerea . This type of luxuriant plants also induces a more humid climate and therefore more favorable to this fungus. In the open field , the sprinkler irrigations carried out rather in the morning - and never in the evening - will allow the plants to dry as quickly as possible.

We will avoid any stress to the plants leading to spurts of growth. The nitrogen fertilizer should be controlled. It will be neither too strong (at the origin of very receptive succulent tissues), nor too weak (sources of chlorotic leaves constituting ideal nutritive bases for B. cinerea ).

Classically, phytopathologists advise eliminate very quickly to plant debris during cultivation , in particular moribund plants bearing one to several cankers on the stem and rotten fruits on which B. cinerea sporulates. It would be desirable to have the same requirements for crop waste. In practice, these are often left on the floor of greenhouses without there necessarily being more damage from gray mold. If you choose this cultivation method, the soil will need to be kept dry so that the leaves do not rot. This option is only valid under shelters. In all cases, the fruits will be quickly eliminated from the crops. At the end of cultivation, all plant debris must be quickly removed from shelters and plots in the open field. In the latter context, this will prevent them from being subsequently buried in the ground and the fungus being able to remain there. A deep plowing facilitate the decomposition of the few remaining waste.

• Next crop

Of course, the measures recommended during cultivation will be systematically applied during the next cultivation. They may be supplemented by the following interventions.

If the nursery is carried out each year in the same place and / or in the same shelter, it will be essential to put in place the measures recommended in the Clavibacter michiganensis subsp. michiganensis .

The polyphagia of B. cinerea , its saprophytic abilities and the fact that the inoculum can come from the culture environment make the efficiency of crop rotations disappointing . In the open field , the soil of future plots will be well prepared and drained in order to avoid the formation of puddles conducive to attacks by B. cinerea on the leaves in contact with the soil. The rows of plantation should be oriented if possible in the direction of the prevailing winds so that the vegetation cover is well ventilated. Avoid setting up the crop with too high densities and injuring the plants. Under shelters , it will be desirable to create a crawl space , to replace plastic any covering the ground and to disinfect the greenhouse carefully (you can consult the sheet Passalora fulva ).

Although the nature of the substrate does not have a direct role in the development of B. cinerea , it should be remembered that organic substrates make it possible to obtain plants that are more vegetative and therefore more sensitive to gray mold.

Regarding fertilization, it was shown that the replacement of nitrate by the chlorides allowed very significantly reduce the damage of B. cinerea in hydroponics in greenhouses. In addition, the calcium enrichment of the tissues of the tomato would greatly reduce its sensitivity to this fungus.

In the open field , we advise you to opt for a system localized drip irrigation , avoiding wetting the vegetation as is the case when sprinkler irrigation is used.

Of preventive fungicide treatments are often necessary greenhouse at certain times of the year to prevent the installation of the fungus ( e-phy ). They can be applied during the first stripping, the same day will be the best. Note that it seems that the lower part of the stem is more sensitive to attacks by B. cinerea . It will be advantageous to particularly protect the wounds caused on the first few centimeters of the stem.

The other diseases and pests must be controlled because they are causing injury, tissue necrosis conducive to the installation of B. cinerea . As soon as the vegetation becomes important, it will be necessary to be vigilant, especially in cloudy weather.

Some sources of resistance have been identified in various countries among the wild relatives of tomato, including Solanum lycopersicoides, Lycopersicon peruvianum and L. hirsutum . The latter species seems to be of particular interest to breeders.

A model based on climate forecasts and named “Botman” is being developed in Israel. This model, coupled with the use of a biological agent - Trichoderma harzianum - makes it possible to control B. cinerea as well as weekly fungicide applications.

A number of alternative and / or original methods have been or are being tested in several countries. For example, compost extracts have been used in Great Britain; sprayed on plants, they would reduce damage caused by B. cinerea and increase yields. Some antioxidants have also been employed in Israel to limit the development of this fungus. The essential oils of lemon were also tested.

Bacteria and several antagonistic fungi have been evaluated in vitro or in vivo to control this fungus. Among them, there may be mentioned Streptomyces spp. As S. griseoviridis Bacillus licheniformis, Candida guilliermondii, Cryptococcus albidus, glutinis Rhodotorula, Aureobasidium pullulans, Gliocladium virens, G. catenulatum, Trichoderma harzianum, Ulocladium atrum, Chaetomium globosum, Clonostachys rosae, Rhodosporidium diobovatum ...

For example, note that biological preparations based on Bacillus subtilis and an extract of Reynoutria sachalinensis would have some efficacy in controlling B. cinerea under shelter in the United States. The combination of a yeast ( Cryptococcus laurentii ) and baking soda would reduce the effects of this fungus after harvest. Finally, it should be that the fungus noted Microdochium dimerium it makes possible to successfully limit the development of B. cinerea , in particular on pruning wounds in plants grown under shelter in France.


* 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.