Control of late blight in organic potato production: evaluation of copper-free preparations under field,growth chamber and laboratory conditions |
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Authors: | Brigitte Dorn Tomke Musa Heinz Krebs Padruot Men Fried Hans Rudolf Forrer |
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Institution: | 1.Research Station Agroscope Reckenholz-T?nikon,Zurich,Switzerland |
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Abstract: | In order to replace copper fungicides in organic potato production, 53 copper-free preparations (CFPs) based on natural compounds,
including plant extracts and microorganisms, and five copper preparations were evaluated for their potential to control Phytophthora infestans, the pathogen that causes late blight of potatoes. In in vitro assays, 30% of the CFPs inhibited indirect germination of
sporangia, 26% mycelial growth and in growth chamber experiments, 21% efficiently reduced foliar blight of tomato plants.
In micro-plot field trials with applications twice a week, the copper preparations were the most effective and reduced foliar
blight by 99%. Of the CFPs tested, Oekofluid P, Mycosin and other sulphuric clays, and C-2000 reduced late blight the most,
from 63% to 37%. In small-plot trials in 2001, 2002 and 2004, 27 CFPs with different formulations and four copper preparations
were examined. In 2004, copper preparations at full and reduced rates and sulphuric clays were applied either weekly or according
to the decision support system Bio-PhytoPRE. With Bio-PhytoPRE, copper preparations reduced foliar blight of potatoes by 23–77%
and increased tuber yield by 2–28%, depending on the copper rate applied and year. With CFPs, maximal efficacy was 17% and
no effect on tuber yield was observed. In vitro and in vivo trials showed that the rainfastness and the persistence of CFPs
was low compared with copper preparations. This indicates that the failure of CFPs under field conditions is probably due
to a lack of stability under prevailing environmental conditions and not to a lack of efficacy. Until stable formulations
for CFPs are developed, an optimised and restricted use of copper fungicides using a decision support system could help to
control late blight in organic potato production and to reduce copper input into the environment. |
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Keywords: | Copper fungicides Decision support system Persistence Phytophthora infestans Plant extract Rainfastness |
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