PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Disease cycle
The sexual Ascomycota state, ie apothecia and
ascospores, has not yet been found in Australia and
only rarely overseas. Spore germ tubes penetrate
and infect leaves in spring, the fungus grows in the
mesophyll and within 2 weeks forms more spores
on upper leaf surfaces. Conidia are produced
throughout the growing season and cause repeated
infections during warm, wet weather.
‘Overwintering’
In susceptible varieties, in lesions on canes, fallen
leaves, and prunings from infected plants.
Spread
Spores (conidia) are spread by wind, rain or
water splash from infected plants and fallen
leaves and prunings from infected plants.
Over long distances, by movement of infected
plants. By the introduction of infected plants
Conditions favoring
Warm (13-24 o C), wet weather especially in spring.
Management (IDM)
Are you a commercial grower or home gardener?
1. Prepare a plan that fits your situation.
2. Crop, region. Recognize variations, some varieties
are more susceptible than others.
3. Identification may be difficult to confirm.
Consult a diagnostic service if necessary (page
xiv). Do not confuse with anthracnose.
4. Monitor leaves of susceptible rose varieties during
damp weather in more shaded areas for the first
signs of leaf spots (page 327). Record results as
recommended. Defoliation caused by leaf diseases
of eucalypts in plantations is monitored. Remember
know when, where, what and how to monitor.
5. Threshold. How much damage can you accept?
Reduction in flower size and numbers may be an
economic issue for commercial growers. Is your
threshold economic or aesthetic?
6. Action. Take appropriate action when any
threshold is reached, eg reduce overhead irrigation,
remove affected leaves, and spray only if a need
has been demonstrated.
7. Evaluation. Review IDM program to see how
well it worked. Recommend improvements if
required, eg change irrigation practices, replace
some very susceptible varieties.
Fig. 198. Disease cycle of black spot of rose (Marssonina rosae).
356 Fungal diseases - Examples of fungal diseases