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Protection methods

  • During cultivation 

Given the rapid progression of Pseudoperonospora cubensis and the risk of damage to the crop, it is essential to react quickly if symptoms of late blight appear on the plants, and if no preventive treatment has been carried out. In fact, the control of this disease, once declared, is difficult because its effectiveness also depends on the climatic conditions prevailing in the crop, the sensitivity of the host and the disease pressure.

An treatment should therefore be carried out as soon as possible fungicide anti-mildew . Several fungicides * can be used alone or in combination ( e-phy ), their effectiveness varies depending on the situation. Initially, it is better to use a systemic fungicide (often combined with one or more contact fungicides) and to maintain a fairly sustained rate, with at least one application per week, especially if conditions remain favorable (dew, rain, fog ...). Subsequently, we can return to contact fungicides.
It should be noted that strains of P. cubensis resistant to some of the fungicides used in the world to control it have already been reported (metalaxyl, mefenoxam, flumorph, dimethomorph, azoxystrobin, enostrobilurin, kresoxim-methyl ... Given the risks of resistance to fungicides which exist in this chromist. It is essential to alternate active ingredients with different modes of action .

In the nursery, the shelters will be ventilated as much as possible in order to reduce their humidity. It will be advantageous to avoid irrigations by sprinkling or by misting. If we cannot do otherwise, they should not be done at the end of the day and in the evening, but rather in relatively warm periods so that the plants have time to dry out before dark.

During cultivation, we will adopt the same recommendations irrigation as those suggested in nurseries. In a greenhouse, everything will be done to avoid the presence of a film of water on the plants; aeration and ventilation will be essential in this type of culture. Basins should be avoided. Under shelters, it is advisable to close the doors before the rains.

At the end of cultivation, plant debris will be removed and destroyed quickly. Crop residues will be buried deep in the soil to promote their rapid decomposition. Cleaning and treating the surfaces of the shelters and the ground may be considered with a product approved for this use ( e-phy ).

  • 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 will be advisable to clean it and treat it as before.
The quality of the plants must be checked on arrival, especially if they come from nurseries located in countries or production areas with a climate favorable to this chromist. If you have the slightest doubt, we advise you to carry out an insurance fungicide treatment.

We will not realize new plantations near melon crops or other sensitive cucurbit already affected. We should also be wary of poorly drained plots, where strong water retention occurs, which is favorable to the development of this disease. In these plots, it will be preferable to improve their drainage before the establishment of 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 planting mounds and / or rows should be oriented in the direction of the prevailing winds in order to promote maximum aeration of the vegetation.

A certain number of other sanitary measures , used alone but especially in combination, make it possible to reduce the progression of late blight epidemics, in particular the elimination at regular intervals of the attacked leaves, and the reduction of the density of the plants.

Given the rapid progression of late blight and the risks it poses to the crop, treatments fungicide preventive (the most effective) will be essential in the nursery, as well as during cultivation. The products used and the rates adopted will be defined with the technician according to local cultivation practices. It should be remembered that the time between two treatments should not exceed 7 to 12 days depending on the active ingredients. Care will be taken to alternate fungicides with different modes of action in order to limit the selection of resistant strains.
If preventive treatments are not carried out, it will be crucial to quickly detect the first attacks of P. cubensis because its epidemics, like those of many mildews, are rapid and very damaging. We will be able to :
- monitor carefully the crops to detect early symptoms, taking care to observe the leaves on both the upper and lower sides;
- also follow the plant health bulletins very closely.
In some countries, early detection of the first sporangia of P. cubensis present in the air would make it possible to anticipate the first cycles of this chromist and to better position the fungicide treatments. It should be added that preventive chemical control will be carried out, in particular in production areas where the disease is severe every year.

Certain polyethylene films, by modifying the microclimate of greenhouses and in particular by reducing the relative humidity of the foliage, would reduce the incidence of downy mildew on cucumber.

Some sources of resistance have been identified in several species of cucurbits and melons (strain MR-1 and some other accessions: 122847 PI 124111 PI 124112 PI 124210 PI, 145594, 165525, PI 197085, PI 197088, PI 288238…). To our knowledge, no variety of melon marketed in France is currently resistant to mildew.

Let us mention some biopesticides which have been tested to control P. cubensis: Bacillus spp., Enterobacter cloacae, Trichoderma harzianum … In addition, for information, several plant extracts are reported in the literature as being able to reduce the development of the agent of mildew: Carya cathayensis , Mikania micrantha , rosemary ( Rosmarimus officinalis ), lemon grass ( Cymbopogon citratus ), basil ( Ocimum bacilicum ), eucalyptus ( eucalyptus globulus ), mint ( Mentha piperita ), marjoram ( Majorana hortensis ), garlic, rhubarb, Piota orientalis , Pinus massoniana , Euphorbia helioscopia , Polygonum hydropiper , Albizia julibrissin , Photinia serrulata , Inula viscosa , Hedera helix , Paeonia suffruticosa …. It would be the same for preparations based on kaolin.

* 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.

Last change : 04/30/21