|Authors: ||S. Keil, M. Zellner, M. Benker|
|Keywords: ||Phytophthora infestans, primary infections, late blight, copper, metalaxyl|
Primary stem infections (stem blight) of potato caused by Phytophthora infestans and initiated by latently infected potato tubers represent an increasing problem in potato production.
Since the exact conditions for the appearance of first symptoms are not yet known, it is not possible to predict when the outbreak of the epidemic will occur.
Even without this knowledge, it is important that preventive measures to control and reduce primary infections are taken.
In order to postpone the occurrence of stem blight and to limit the early spread of the disease, the use of seed treatments and well-timed applications of fungicides were compared.
Field trials were carried out between 2004 and 2007 at two sites in Bavaria.
A total of 23 experiments were implemented with artificially infected seed tubers, or alternatively, with a severely infected tuber planted as an inoculum source adjacent to healthy seed tubers.
Two seed treatments were tested: copper hydroxide (trade name: Cuprozin flüssig or metalaxyl M + mancozeb (trade name: Ridomil Gold) was used at a concentration of 120 g/ha.
Alternatively, an early fungicide application was performed with metalaxyl M + mancozeb (2 kg/ha) as soon as P. infestans in the stem was detected by PCR. Disease was assessed by visual detection of stem blight, which was done weekly.
The best result in reducing the frequency of stem blight was achieved by early application of the systemic fungicide.
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