Agriculture Reference
In-Depth Information
Control
Control of Botrytis is based on canopy management and chemical sprays. Closed
canopies where the fruit is shaded and does not dry after rain is more susceptible
than fruit in open canopies. Canopy management is thus a major tool used in the
control of this disease (English et al.
1993
). Use of chemical sprays is widespread,
but this particular fungus is very adaptable to its environment and so resistance to
many of the fungicides used to control Botrytis has developed (Latorre and Torres
2012
; Leroch et al.
2011
; Rosslenbroich and Stuebler
2000
).
Noble Rot
In some circumstances incidence of Botrytis on grapes is desirable (Thibon et al.
2009
). If the fungus colonises the bunch at the end of the growing season in autumn,
and if conditions are dry, then a type of rot occurs that is termed noble rot. Typically
noble rot occurs in temperate climates where damp conditions occur early in the
morning followed by warm afternoon sunshine. In this situation the fungus grows
very slowly on the surface of the fruit without invading the tissue. The fungus de-
hydrates the fruit, concentrating the sugar and forms glycerol. Glycerol is a simple
molecule that is viscous and enhances the sweet sticky characters of the fruit. Dehy-
dration of the fruit can further be enhanced by wind. Typical varieties of grapes that
are used for noble rot include Riesling, Semillon and Sauvignon Blanc.
Powdery Mildew
Symptoms and Infection
Symptoms of powdery mildew include a white fungal growth on the upper surface
of vine leaves (Gadoury et al.
2001
). Aside from affecting the leaves, powdery mil-
dew can also occur on pre-veraison berries. As the berries mature post-veraison,
earlier powdery mildew infections can result in scarring of the fruit (brown web-like
markings). The disease is caused by the fungus
Uncinula necator
and is sometimes
referred to as Oidium. The disease begins around bud burst on developing foliage,
and if unchecked can result in a serious loss in photosynthetic function of the vine.
Infected berries have a white covering of powdery growth. At the end of the grow-
ing season the disease over winters as specialised structures called
cleistothecia
in
woody tissues such as the bark and dormant buds. These infected buds then give
rise to more disease the following season after bud burst. The disease can develop
under a range of environmental conditions. As with botrytis, the disease results in
wine with mouldy fungal characters (Stummer et al.
2003
). Powdery mildew is an
obligate parasite, growing only on grapevine material.
