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Prospecting for new fungicides to control apple scab
(Venturia inaequalis) in organic fruit growing.
M. Bengtsson1, B. Heijne2, P.F. de Jong2, H.J.L.Jørgensen1, K. Paaske3, H.L. Pedersen4, M. Trapman5, E. Wulff1 and
J. Hockenhull1
1Department of Plant Biology, The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark: mvb@kvl.dk;
2AppliedPlant Research (PPO-fruit), Randwijk, The Netherlands; 3Danish Institute of Agricultural Sciences, Flakkebjerg, Denmark; 4Danish Institute of Agricultural
Sciences, Aarslev, Denmark; 5BioFruitAdvies, Zoelmond, the Netherlands.
INTRODUCTION
Apple scab, caused by the fungus Venturia inaequalis (Cke.) Wint., results in serious losses
in quality and yield of organically as well as conventionally grown apples. Organic apple
growers are highly dependent on the use of sulphur, lime sulphur and copper fungicides to
control apple scab. Only elemental sulphur is permitted for scab control in organic apple
production in Denmark, whereas also lime sulphur is permitted in The Netherlands, and
copper fungicides are used in organic production in many other European countries.
However, the use of copper fungicides in the EU is now being phased out (Council Regulation
(EEC) No 2092/91) and alternative fungicides for control of apple scab and diseases in other
crops are increasingly needed.
As part of the EU project REPCO (Replacement of Copper Fungicides in Organic Apple and
Grapevine Production in Europe, 2003-7; www.rep-co.nl) we are prospecting for plant
extracts and other materials, including disease resistance inducers, for apple scab control in
organic fruit production.
MATERIALS AND METHODS
SEARCHING: FIELD TESTING:
Novel and pipeline products with potential for apple scab Promising materials are further tested in small
control, including plant extracts acting as organically scale field trials in organic orchards at DIAS,
based fungicides and resistance inducers, are continuously Aarslev, Denmark, according to EPPO-guidelines.
searched for. Before working with a material, it is first During the main period of ascospore discharge
being subjected to a preliminary database screening for (May-June), treatments are applied at 3-5 day
toxicological risks, economic feasibility and acceptability intervals on trees of ‘Jonagold’ with a specially
for use in organic growing. built tunnel sprayer. Sulphur and copper are used
as reference treatments. Scab is assessed on spur
SCREENING: leaves, extension shoot leaves and fruits at
Two routine screening assays are used, one testing the harvest. Phytotoxicity on leaves and russeting on
effect of materials in different concentrations on conidial fruits is assessed as well.
germination on glass slides, and one testing the effect of The most promising compounds are finally trialled
compounds on disease expression on leaves of apple in a modern integrated organic orchard system at
seedlings (‘Golden Delicious’). Test solutions are applied PPO, The Netherlands, in which compounds are
either one day before or one day after inoculation with applied in combination with sulphur according to
conidia. Sulphur and water are used as reference the warning system RIMpro. Copper and sulphur
treatments. Disease symptoms are scored according to a are used as references.
standardised scale two weeks after inoculation.
RESULTS & DISCUSSION
Over 100 plant extracts and other materials have been tested in the screening assays.
Among the materials that inhibit conidial germination in the glass slide tests many have
either no or only a low effect in the plant assay. However, a number of promising
materials have been identified and these include several plant extracts from plant species
from different taxonomical groups and geographical origins. In many cases the efficacy is
most pronounced as preventive treatments and less as curative treatments, which is also
the case with sulphur treatments.
Several materials have been selected for the field trials, and a few plant extracts and
pipeline products have been identified as promising new materials for apple scab control.
One material that has consistently shown very good control efficacy is based on extracts
from yucca. To facilitate product development, a patent application has recently been
filed concerning the use of yucca extracts as fungicides.
In addition to optimisation, timing and formulation of materials, studies on mode of action of promising materials are under
investigation. Especially, we are on the lookout for materials that seem to operate as resistance inducers in apple.
ACKNOWLEDGEMENTS
REPCO is partly funded by the 6th Framework of the European Commission (Project No 501452). Project Officer: Danièle Tissot Boireau, DG RTD Unit
E03 Safety of Food Production Systems, SDME 8/22 Belgium, e-mail daniele.tissot@cec.eu.int . The information contained in this poster reflects only
the authors’ views. The Community is not liable for any use that may be made of the information provided therein.
REPCO project co-ordinator: J. Köhl, Plant Research International, Wageningen, NL, e-mail jurgen.kohl@wur.nl
