Expert advice

Controlling alternariosis and potato blight

Some of the main diseases found at potato plantations include alternariosis and potato blight. Under favourable conditions, they are very common, and their economic importance is high. On plantations, if mistakes were made in terms of fungicidal protection, or if it was not utilised at all, the losses of the crop may be high. In extreme cases the reduction in crop yield for the bulbs may even amount to 70%. It is necessary to assume the right strategy against the causal agents of these diseases.

Controlling potato blight

The fungus phytophthora infestans is responsible for potato blight; during the growing season, it may attack all parts of the potato plant: the leaves, stalks and during storage it may be found on the bulbs. The disease develops quickly on plantations, and its source may be leftovers of infested plants from the prior growing season or plants growing from ill bulbs. The disease spreads very easily also from infested plants to neighbouring, healthy plants – leading to quick infection of all plants across a plantation.

Potato blight develops under very high air humidity due to rain, fog or dew at temperatures of approx. 12-15 ᵒC, with the optimum temperatures being 15-18 ᵒC. The first signs can be noticed on lower leaves in the form of irregular, grey-green spots, which, as time passes, become brown and gain a light-green circumference. The underside of the leaves is covered with a white-grey coat. Under favourable weather conditions, the symptoms of potato blight may be found also on stalks and leaf petioles. The pathogen from the overground part also attacks the bulbs, on the surfaces of which one can notice grey spots. Bulbs attacked by potato blight rot more quickly in storage.

Controlling alternariosis

It is caused by the fungi alternaria solani – the cause of dry leaf spot, and alternaria alternata – the cause of brown leaf spot. Differently than potato blight, infection with the causal agents of alternariosis occurs at higher temperatures, with the optimum value being approx. 25 ᵒC at high air humidity. The signs of the disease caused by alternaria solani are visible first on older leaves in the form of small spots, clearly separated from the living portion of the leaf. In the centre one can see circles, akin to tree rings.

As the disease progresses, the spots become larger and start to show up on younger leaves. The presence of the fungus alternaria alternata, in turn, is exemplified by numerous tiny spots on the surface of the leaf and stalk. With time, necrosis sets in where the spots are – the leaf crumbles, which, in case of a heavy infection, can lead to total destruction of the leaf. The fungus may also attach the bulbs, however, they only show the symptoms during storage – as grey-brown, deep spots. The source of infection at the plantation may be ill plant remains and infected seed potatoes used for planting.

In the case of both these diseases, to save the crop, one needs to ensure appropriate chemical fungicidal protection. The decision to perform a treatment should be preceded by a field visit or current signals. In case a disease is of low intensity, it might be sufficient to use the product Ekonom MC 72,5 WP at 2.0 kg/ha, which works on the surface and inside. In case the treatment would need to be repeated, the product may be used three times during the growing season. In case of heavy infection and intense growth of the crop, use rather the product Ekonom 72 WP/Ekonom MM 72 WP at 2.0-2.5 kg/ha, and in case of a heavy infection, the treatment must be repeated. Ekonom 72 WP/Ekonom MM 72 WP operate both on the surface as well as systemically – the active substance moves together with the juices in the plants, also protecting new growths against infection even up to 7-10 days.
A particular differentiating factor of the Ekonom series is the fact that different than many fungicides for potatoes, it protects them and at the same time controls the two most dangerous fungal diseases in the production of potatoes.

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