![]() ![]() At Debre Berhan agricultural research center, the highest area under disease progress curve (AUDPC) value (948.8%-days) was computed from untreated control plots of Gudene variety while the lowest AUDPC value (223%-days) was computed from Gudene variety treated with Ridomil Gold. Disease severities, disease progress curves, disease progress rate, and tuber yield were significantly ( Pā<ā0.01) affected by potato varieties, fungicide applications, and their interactions at both locations. ![]() Three potato varieties and five fungicides including untreated control were arranged in a randomized complete block design in three replications at two research locations during the 2019 season. Field experiments were conducted to evaluate potato varieties and fungicides for the management of late blight. It exists a widespread resistance by Alternaria Species against by fungicide Ortiva and Signum therefore it should be applied only once.Potato production is limited due to late blight of potato. Signum is registered for maximal four and Ortiva for maximal three treatments. The best effectiveness is achieved if the additive is used in the second and fourth (under difficult terms possibly again for the fifth or sixth) late blight spraying. If the spraying scheme, as used for late maturing varieties, is composed of products without sufficient side effects on Alternaria (Banjo Forte, Carial Flex, Infinito, Ranman Top, Revus or fluazinam-containing fungicides) and if during the growing season heat and drought stress can be expected then a spraying mixture of Phytophthora fungicide plus Signum or Ortiva can be efficient. Based on our long-time test results, if these products are applied almost exclusively, it is not necessary to add special products in general. Many of the approved products against late blight have a sufficient side effect on Alternaria (see pdf-documents Comparsion of Contact and Systemic Late Blight Fungicides). However, in general Phytophtora and early blight can not be considered independently. Therefore checking the own potato crops for primary herds and early infections still is a must and should be done once or twice a week starting three weeks after emergence of the potatoes and depending on the infection pressure (forecasting model). Other factors ā such as local particularities in the weather or variations of the soil moisture - caused by a high groundwater level for example ā must also be considered. However it is not enough to rely on the calculated forecast exclusively. This information is available at in Bavaria and at for most of the other German states. The potato blight forecasting, offered by the official Plant Protection Service, is an important tool to determine the optimal moment for the first spraying. Treatments carried out too late often do not have a sufficient effect. Treatments carried out too early cause expenses without achieving an effect against the disease. This should be about one week before the visible initial infestation in the plot. It is very important to start with the spraying against late blight at the right moment. Beyond that the removal of potato volunteers and waste heaps is a reasonable phytosanitary measure. This is an important step to delay the occurence of late blight in the potato crop as shown in current research work at the LfL. What can those working in this field do? Farmers, who have treated their seed potatoes with Cuprozin progress against bacterial soft rot (Erwinia) with the ULV-method (Mantis implement) can count on a side effect against an initial infection (stem infection) of Phytophthora. Sites with a high ground-water level and areas with high rainfall are especially endangered by a very early and massive infestation of the stems. Light soils drain water faster and the danger of an early and heavy infestation is considerably lower than on loamy soils. But also the soil type indirectly affects the progress of the disease. ![]() This is why in years with dry weather in spring a considerably lower initial infestation and with that a lower impact of infections occurs than in humid years. In both cases the plants show an infestation of the stem very early (initial infestation). They will grow up diseased as well and typical Phytophthora nests develop. This is how neighbouring plants or stems of the same plant can be infected. Spores develop on the diseased tuber and are distributed via soil water. Extensive research activities at the Bavarian State Research Centre of Agriculture (LfL) in recent years have shown that with high soil moisture another way of infection is possible (fig. When these potatoes start growing in spring the fungus expands into the stem. The late blight pathogen (Phytophtera infestans) hibernates in latently (not visibly) infected potato tubers. ![]()
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