Agriculture Reference
In-Depth Information
spores (oospores) occur less frequently and can remain
viable for a long time. All species of
Phytophthora
have
a soil-borne resting phase. Some species, such as
P. palmivora
, also produce sporangia, which disperse aerially
and cause stem cankers, leaf blights and fruit rots. Other
species, such as
P. cinnamomi
, are mostly soil-borne and,
usually, infection is confined to the roots and lower trunk.
Zentmyer GA (1980)
Phytophthora cinnamomi and the
diseases it causes.
APS Press: St Paul, Minnesota.
POWDERY MILDEWS
■
Powdery mildew is probably the most common of all plant
diseases. The characteristic white, powdery growth occurs
on plants as diverse as cereals, trees, turf grass, woody
ornamentals and most fruit and vegetable crops.
Hosts
Phytophthora
species are responsible for major diseases
in avocado, citrus, pineapple, papaya, passionfruit,
macadamia, olive and strawberry. They also infect stone
fruit, fig and mango.
Cause
Although the symptoms of powdery mildew are similar on
many hosts, several fungal species cause the disease. Many
are host-specific, often infecting only a few, related species.
The main genera of fungi causing powdery mildew
diseases include
Erysiphe
,
Leveillula
,
Oidium
,
Podosphaera
,
Sphaerotheca
and
Uncinula
.
Management
Usually, an integrated disease-management approach to
control Phytophthora is used in horticulture. Severe
disease development requires a source of primary
inoculum, susceptible host plants, warm temperatures,
high humidity and temporary f flooding. Use the following
disease-management procedures:
Exclude the disease by using strict quarantine procedures
and pathogen-free planting material schemes.
•
Plant resistant varieties and rootstocks, where these are
available.
•
Provide orchard conditions that favour the host over the
pathogen. For example, improve soil drainage to reduce
temporary fl ooding, provide adequate nutrition to
stimulate plant growth, apply organic matter to
stimulate antagonists, predators, hyperparasites and
competitors in the soil, increase tree spacing and practise
canopy management.
•
Fig 2.18 Powdery mildew on new growth of apple leaves, showing
the characteristic, upward curling in leaves.
Maintain good orchard hygiene to prevent secondary
inoculum building up and the pathogen spreading.
•
Apply recommended chemicals.
•
Further information
Brown B (1999) Occurrence of
Phytophthora cinnamomi
and
other Phytophthora species in rainforests of the wet tropics
world heritage area, and of the Mackay region, Queensland.
In
Patch death in tropical Queensland rainforests.
(Ed.
P Gadek) pp. 41-76. Rainforest Research Centre: Cairns.
Drenth A & Guest DI (2004) Principles of Phytophthora
disease management. In
Diversity and management of
Phytophthora in south east Asia.
(Eds A Drenth & DI Guest)
pp. 154-160. ACIAR: Canberra.
Menge JA & Nemec S (1997) Citrus: Phytophthora root rot.
In
Soilborne diseases of tropical crops
. (Eds RJ Hillocks & JM
Waller) pp. 185-227. CABI Publishing: Wallingford.
Fig 2.19 Powdery mildew mycelium on a strawberry fruit.
