PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Disease cycle
The ‘conidia’ produced are not really conidia but
bud spores produced when previous ascospores
proliferate by budding (Fig. 201 below) and the
fungus survives summer as ascospores. These
germinate in autumn rains and form yeast-like
spores that can ‘overwinter’ in bud scales and on
twigs. These spores infect the newly developing
leaves in spring if the following weather is warm
and humid during early blossoming. It appears that
the expanding leaves are only susceptible when
they are young; they become resistant to infection
as they age.
‘Overwintering’
Spores (‘conidia’ and ascospores) of the fungus
mainly ‘overwinter’ on bud scales.
Spread
Spores are spread by wind and water splash onto
emerging leaves. As nearly all susceptible varieties
are infected, peach leaf curl is spread by the
movement of infected nursery stock.
Conditions favoring
Cold, wet weather during leaf emergence in
spring followed by warm, humid weather during
early blossoming in spring.
Disease ceases with high summer temperatures.
However, if weather again becomes favourable
further disease may develop on new leaves.
Tissue is only susceptible when young. Tissue
becomes resistant to infection as it ages.
Fig. 201. Disease cycle of peach leaf curl (Taphrina deformans).
Fungal diseases - Examples of fungal diseases 359