Expert advice

Alternariosis and potato blight

The main diseases of the potato necessarily include alternariosis and potato blight, which constitute a threat to every plantation. In the production of potatoes, if one made mistakes in terms of fungicidal protection, the losses of the crop may even amount to 70%, hence it is necessary to assume the right strategy against the causal agents of these diseases.

Potato blight

    The fungus phytophthora infestans attacks all parts of the potato plant: the leaves, stalks and the bulbs. The disease develops quickly, and its source may be leftovers of infested plants from the prior growing season (e. g. from a different field) or plants growing from ill bulbs. The disease spreads very easily 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.

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 healthy 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.

In order to protect one's plantation against the causal agents of alternariosis and potato blight, one needs to conduct comprehensive and effective fungicidal protection. The decision to perform a treatment should be preceded by a field visit or current signals – such a solution will permit one to fully utilise the preventive action of a product. In case a disease is of low intensity, it might be sufficient to use the Ekonom MC 72,5 WP (mancozeb and cymoxanil) 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 (mancozeb and metalaxyl) 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.

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