Protection methods

•  During cultivation

As soon as the very first spots of observed mildew are , treatments fungicide * must be carried out immediately. It should be remembered that curative treatments, with relative effectiveness, more easily generate the appearance of strains resistant to fungicides. Preventive treatments are preferred to them. Several active are used to control ingredients Bremia lactucae ( e-phy ), alone or in combination:

- Contact fungicides , and in particular several dithiocarbamates (maneb, mancozeb, metiram zinc, etc.). These are not effective products with regard to this mildew. For them to be relatively effective, they must be applied weekly. They still have the advantage of being quite versatile and not being affected by resistance phenomena. The use of these fungicides has been limited and / or highly regulated because they are the source of residues in lettuce;

- Penetrating and / or systemic fungicides such as cymoxanil, propamocarb HCl, fosetyl-aluminum, azoxystrobin, benalaxyl.

The recommendations for treatments on lettuce most commonly proposed by technicians to control mildew in France are as follows:

- Nursery application
From germination, 2 sprays / week mainly with mancozeb.

- Application just before planting, after the last watering
Use more effective active ingredients such as, for example, the combination dimethomorph + mancozeb, cymoxanil + mancozeb or propamocarb HCl + fosetyl-aluminum ...

- Application during cultivation
On resumption, then in stages 7-9 leaves , 11-13 leaves , 16-18 leaves.


In the nursery, we can try to contain the first outbreak (s) by treating them with a more concentrated dose of a fungicide and eliminating the affected seedlings. Plants produced under such conditions will only be marketed if the mildew attack has been completely contained and by warning the buyer producers of the risks involved.

In addition to fungicide treatments, a number of prophylactic measures should be applied.

- In the nursery , the shelters will be ventilated as much as possible in order to reduce their humidity. It will be in your interest to avoid sprinkling irrigations late in the evening and especially in the morning, because contaminations preferably take place during the morning. If this is not possible, they will be carried out in warm weather and early enough in the afternoon so that the plants have time to dry out before dark.

- In cultivation , we will adopt the same irrigation recommendations as those suggested in nurseries. In a greenhouse, it may be necessary to heat in order to reduce the ambient humidity. Everything will be done to avoid the presence of a film of water on the plants.

At the end of the crop, a maximum of plant debris should be removed quickly; the remaining residues will be buried deeply in order to promote their decomposition.

•  Next crop

The next nursery will be set up in a sunny location, in no case damp and shady. If it takes place in the same shelter as the previous year, it is advisable to apply the recommended hygiene and disinfection measures .

In cultivation planting , avoid crops in poorly drained plots where there is strong water retention and in soils that are too rich in organic matter. Crop rotations of at least 3 years are recommended. New plantings will not be made near already affected salad crops. The manures made must be balanced, in no case excessive. In countries or regions where this is possible, planting densities can be reduced in order to have more aerated plots, in which the humidity within the plant cover will be lower. If possible, the plantation mounds should be oriented in the direction of the prevailing winds in order to promote maximum aeration of the vegetation. Wild lettuce species will be eliminated from the plots and their environment.

Given the speed of progression of this mildew and the risks it poses to the crop, preventive fungicide treatments ** will be essential in crops, as in nurseries ( e-phy ). The choice of products and rates used will be defined with your technician according to local cultivation practices. It should be remembered that the time between two treatments should not exceed 12 days. Particular care should be taken when pesticides are mixed together or when treatments are carried out in extreme climatic conditions: there is a risk of incompatibility between products and of phytotoxicity. Dithiocarbamates, posing residue problems, can be used primarily at the very beginning of cultivation: in the nursery and immediately after planting. Care will be taken to alternate fungicides with different modes of action in order to limit the selection of strains Bremia lactucae resistant .

Of resistant varieties are available in several countries, including France. They have several resistance genes in order to control the many races present in the field *. A summary of the genes used and the breeds described can be consulted in the section "Resistance of lettuce to pathogens" . In some countries, the status of the breeds present is not known. It will be necessary to carry out experiments locally in order to define whether the resistant varieties chosen will make it possible to control the autochthonous races. In fact, although representing a real asset, these varieties should be used in concert with a complementary chemical control.

Please note: the situation of resistance to late blight on lettuce seems to be evolving in certain regions.

* Recently the IBEB (International Bremia Evaluation Board) announced in August 2013 the existence of 3 new races of this stramenopil, bringing to 31 the number of known pathotypes in this organism.

* * As the number of pesticides available for a given use is constantly changing, we have nevertheless chosen to indicate to you in each sheet the name of a few active ingredients approved at the time of writing. We will try to update this list, as withdrawals and new approvals occur. Despite this, 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.