slight effects at the dosage which is recommended
by the manufacturer. However, efficacy at lower
dosages in indoor screenings is necessary, if any
activity in the field may be expected.
Based on the results of the indoor screening trials
10 out of 39 test substances were recommended to
be tested under field conditions. Priority was given
to products which with proven activity and high
efficacy as well as availability and formulation.
Results of field screenings 2004 and 2005:
The first symptoms of grapevine downy mildew
were observed on June 14th in 2004 and on May 30th
in 2005. In 2004 disease pressure was high; disease
incidence reached 100% in the beginning of August
in the untreated control. In 2005 disease pressure
was even higher, in the untreated control, disease
incidence reached 100% already in mid of July.
In both years the reference treatments with copper
(Cuprofix 2004, Kocide DF 2005) and with a
systemic fungicide (Aliette) gave good protection of
the grapevine plants against downy mildew (Fig. 1).
The use of Aliette is not an official strategy, but this
product is included because of its systemic mode of
action. The total amount of copper used during the
season 2005 was 6.8 kg per ha, which is more than
the maximum of copper allowed in Switzerland.
The use of a reduced amount of copper (‘Strategy
Low Copper’ 0.4 kg/ha and year) gave a good pro
tection against Plasmopara on leaves; however protection
of the grapes was not sufficient with this
copper concentration. Treating the grapevine plants
first with Mycosin plus Stulln Sulphur and later on
with Copper (2.8 kg Cu/ha yr) protected leaves and
grapes well from downy mildew of grapes.