Spain: Potato growers on edge due to a plague that destroys crops every year

In other words, any spread of this pest could result in losses of millions of euros. Worst of all, current weather conditions are facilitating its expansion. For all these reasons,  the Ministry of Agriculture  has already published a guide for managing these potato diseases.

Why is potato blight such an aggressive plague in Spanish agriculture?

Potato blight, also known as late blight, has found the perfect conditions to develop in Spanish fields. Its ideal environment is characterized by temperatures between 10 and 27°C.

Another contributing factor is humidity exceeding 90% for two consecutive days. This is precisely the environment typically found in spring in much of the growing region.

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But the problem isn’t limited to potatoes. The fungus can also attack tomatoes or onions, which in turn have to defend themselves against  other types of pests .

The outbreak usually originates in infected tubers from previous seasons or in contaminated seed potatoes. From there, the spores spread with astonishing ease: wind, rain, fog… climatic conditions favor their expansion.

The truth is that practically any element can serve as a vehicle for the pathogen to jump from one plot to another in the blink of an eye.

Symptoms that potato blight is destroying the tuber

Detecting downy mildew early is vital to avoid disaster. Although in its early stages it can be confused with other diseases, its symptoms are quite characteristic.

Small, irregular spots appear on the leaves, first pale green, then darker, surrounded by a yellowish halo. On the underside of the leaf, a fine white fuzz is commonly observed, a cottony mycelium that reveals the presence of the fungus.

When the temperature exceeds 20°C and the humidity is very high, these spots grow rapidly and can completely necrotize the leaf.

On the stems, elongated lesions form, dark green almost black in color, with a glassy and fragile appearance. Some exceed 10 centimeters and can easily rupture the tissue.

In the case of tubers, if the infection progresses unchecked, brown spots appear on the skin that penetrate up to two centimeters inward. Within a few days, the tuber rots, resulting in the total loss of the crop.

How to prevent an uncontrolled potato infestation

Prevention is the only real way to gain time against downy mildew. The first step is to use certified, healthy seed potatoes, and to choose varieties with good tolerance.

It is also key to remove any plant remains from previous campaigns that could serve as a reservoir for the fungus.

If downy mildew appears or is at risk, it’s best to apply fungicides. Contact fungicides act on the leaf surface, while systemic fungicides penetrate the plant and offer protection for up to two weeks.