Late blight (or downy mildew) is one of the worst diseases that can affect the tomato plant, in certain climatic conditions it can become a real scourge and even destroy the entire harvest.
This problem is a cryptogamic (i.e. fungal) disease, caused by a pathogen whose scientific name is Phytophthora infestans. Besides tomato crops, it can affect other vegetables, including the nightshade family ( potatoes , eggplant ). There are also other strains of downy mildew that attack other crops,
The damage this pathogen can cause to tomatoes is potentially devastating. , in 1800 in Ireland mildew was even the cause of a famine, but it is possible to take measures to prevent it and protect the garden. Even once mildew has appeared, if measures are taken in time, it can also be contained with treatments authorized in organic farming.
Here we will deepen, learn to recognize the symptoms late blight on tomatoes and learn how carry out a preventive defense and fight with natural methods . Typical mold treatment is based on copper products, such as copper oxychloride . If it is true that this fungicide thwarts the disease and is authorized by organic regulations, you should also know that you should not abuse it because it accumulates in the soil. The intention of this article is to learn not only how to defend tomatoes organically, but also how to do it consciously, for a truly eco-sustainable garden.
Phytophthora infestans: tomato downy mildew
The causes of the disease
Recognition of symptoms on plant and fruit
Late blight prevention
How to control tomato late blight
Biological treatments against mildew
How and when to treat copper
Phytophthora infestan: late blight on tomatoes
If we want to be effective in the prevention or the fight against this disease, the first fundamental thing is above all to “know the enemy “. Therefore, we must learn to identify the problem from the first symptoms and, above all, to know the climatic conditions favorable to the pathogen, in order to understand the cases in which it occurs more frequently.
tomato late blight it’s a cryptogamic disease caused by a pathogenic fungal microorganism belonging to the piziaceae family and called Phytophthora infestans . This same fungus also attacks plants other than tomatoes, especially from the nightshade family, especially with eggplant, potato and tar . Pepper doesn’t seem to be subject to it.
The term “mildew” is rather generic: it is used to describe a number of plant diseases, for example onion blight. (Destructive Peronospora) or cabbage blight (Peronospora brassica). Interestingly, most late blight is caused by fungi from the Peronosporaceae family (hence its name), but tomato late blight is caused by an agent belonging to the piziaceae. From this we learn that late blight is not a single disease: the infestation that affects tomatoes is not transmitted to onions, but can be transmitted to eggplants and potatoes since they are also likely to Phytophthora . This information is important when crop rotations are planned, as we will see when we talk about prevention.
The causes of the disease
The cause of pathology, as we have seen, is the microorganism Phytophthora infestans , almost always present in the soil. When this proliferating fungus manages to attack the plant in a significant way and the disease manifests itself, it is interesting to know what are the factors that favor the pathogen . The main factors causing the problem are humidity and temperature.
- excessive humidity . Excess water, when it stagnates in the soil and especially when it persists in the aerial part of tomato plants, is the main cause of tomato late blight. Nighttime humidity that lingers in the dew is particularly dangerous.
- Temperature . The microorganism is activated by heat, especially by changes in temperature.
When the right temperature is reached in the garden with high humidity, the plants get sick easily. At this time, preventive and protective treatments should be carried out to protect the tomatoes. The worst period is usually late spring (May and June) and especially late summer (late August).
Recognize symptoms on plants and fruits
This disease appears first on the leaves tomato. It starts with a localized yellowing in patches looking at it against the light, we see that the spots modify the density of the leaf tissue and are translucent. The spots then turn brown and over time the leaf dries out completely.
mildew then attacks the stem and the fruit , ruining the crop and killing the plant. In the fruit of the tomato we recognize downy mildew black dots in brown.
Alternaria is another typical tomato disease, it can be distinguished from late blight because the spots are concentric, with well-defined borders and yellow halos at the edges.