Journal of Plant Pathology - Sipav.org

S1.32 Efficacy of sprays against grapevine powdery mildiew Journal of Plant Pathology (2011), 93 (1, Supplement), S1.29-S1.32
(RW%) was only 40% in spite of a relatively low disease
pressure in this year. Yet, 7 sprays had the same low effect.
These technical problems in 2002 showed clearly,
that errors in this period are extremely risky in that infections
could not be cleared by further sprays.
During OWP, growers need to work very accurately
against powdery mildew closing the open window, especially
if weather conditions are suitable fungal attacks.
The biggest problems may be caused by infections at
the beginning of this period. If the rachis is colonized
by the fungus, sporulation will occur when young
berries are extremely susceptible (Fig. 1).
During the OWP, fungicides against powdery mildew
should be used at short spray intervals, especially if the
weather conditions are suitable for the fungus. All
sprays at other times had a very low relevance for the final
disease levels. These notions were integrated into
the expert system OiDiag 2.2 as an ontogenetic part index
(Kast and Bleyer, 2010). The strong decrease of index
values after fruit set demonstrates the decreasing
susceptibility of grape clusters.
REFERENCES
Fig. 1. Sporulation of powdery mildew (Erisyphe necator) on
the rachis of a grapevine bunch.
BBCH55 to BBCH73 are sufficient to control the disease
on grape clusters and that further sprays provide
hardly any benefit. For a better understanding of this
problem we propose to introduce the name of “Open-
Window-Period” (OWP) for the period starting one
week before flowering and ending a few days after
berries reach 2 mm in diameter (period from BBCH55
to BBCH73). A vine-grower should keep this window
covered by his spray program. During OWP, growers
need an absolutely effective and sure powdery mildew
spray program. Therefore, we recommend using the
best fungicides during this period. Other fungicides
may only be used for further sprays to reduce the production
of cleistothecia on the leaves in order to reduce
the overwintering potential.
Since an accident with the tunnel sprayer caused
technical issues, a gap in the spray schedule of 18 days
beginning 10 days before flowering (BBCH55) occurred
in 2002. The next spray in all treatments was at the end
of anthesis (BBCH69). The effect of three sprays
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