Plant Protection 3 : Selected Ornamentals, Fruit and Vegetables

Carnation
Dianthus spp.
Family Caryophyllaceae (carnation family)
PESTS AND DISEASES
Parasitic
Virus and virus-like diseases
Bacterial diseases
Bacterial leaf spot
Fungal diseases
Anther smut
Damping off
Downy mildew
Fungal leaf spots
Fusarium blight and bud rots
Fusarium wilt
Grey mould
Rhizopus soft rot
Root and stem rots
Rust
Nematode diseases
Cyst nematode
Root knot nematodes
Insects and allied pests
Aphids
Caterpillars
Mites
Thrips
Snails and slugs
Non-parasitic
Calyx splitting
Environment
Nutrient deficiency, toxicity
Pesticide injury
PESTS AND DISEASES
Parasitic
VIRUS AND VIRUS-LIKE DISEASES
Most commercial carnation crops are affected by
virus diseases, most of which are restricted to
carnations. Plants may be infected with more than
one virus. Virus diseases are important, reducing
flower quality and yield by as much as 40-50%.
Some cultivars infected with virus make
reasonable growth if well cared for, but tend to
deteriorate and are a source of infection for other
plants. Symptoms vary with the virus(es) involved,
the cultivar, stage of growth and climate. Their
presence can only be confirmed by viral diagnostic
tests. Leaves and stems may show mottling,
streaking and other symptoms. Flowers may have
an increased incidence of colour breaks and calyx
splitting. All carnation viruses are spread by
vegetative propagation from infected plants, by
grafting, but usually not by seed, some also by
insects and by sap.
Carnation mottle virus (CarMV) is the most
common virus of carnations in Australia. Infected
plants are mostly symptomless but some cultivars may
show leaf mottling and a variable colour intensity in
petals. CarMV is also spread by sap transmission
during handling, by contact between plants (roots or
foliage contact), there is no vector.
Carnation etched ring (CERV), carnation latent
virus (CarLV), carnation necrotic fleck virus
(CarNFV) carnation vein mottle (CarVM), may
cause necrotic rings, flecks, spots and mottles on
leaves and flower breaks, but often there are no
symptoms. Multiple infections of these viruses can
make symptoms more obvious. CERV is also spread
by aphids, by mechanical inoculation, not by contact
between plants; CarLV also by aphids, eg green peach
aphid (Myzus persicae), by mechanical inoculation,
not by contact between plants; CarNFV also by
aphids, by mechanical inoculation with difficulty, not
by contact between plants; CRSV also by mechanical
inoculation, by contact between plants, not by a
vector; CarVM also by aphids, mechanical
inoculation, not by contact.
Others: Many more viruses occur in Australia and
overseas, eg tomato big bud mycoplasma (Fig. 25).
See Annuals A 4.
BACTERIAL DISEASES
Bacterial leaf spot, bacterial leaf and flower
blight (Pseudomonas andropogonis = P. woodsii) is a
common and serious disease in cooler areas.
Some strains are more virulent than others.
Ornamentals, eg carnation, statice, gypsophila,
bougainvillea, Ceratonia siliqua, Cicer arietinum,
Mucuna deeringiana, field crops, eg Sorghum spp.,
Trifolium spp., Vicia spp., red and white clover, chick
pea. Some strains are more virulent than others.
Initially leaf spots are watersoaked and dark green,
later centres become pale brown and have a purplish
margin. Spots are up to 10 mm in diameter and may
join together to form irregular dead patches, leaves
may die. Calyx infection may result in damage to
the flower and stems may be girdled. Old foliage,
stems and flower buds are severely affected, severely
infected plants die. Favoured by wet weather, warm
temperatures (20-25 o C) and by wounding. Avoid
growing carnation with statice, gypsophila or
bougainvillea. Plant cultivars with some resistance,
many new Mediterranean cultivars are susceptible
(Trujillo and Nagata 1994). Effective bactericides are
not available. See Vegetables M 5.
Others: Bacterial wilt (Pseudomonas caryophylli)
was introduced on plants imported from an approved
overseas source. Fasciation (Corynebacterium)
causes a proliferation of short spindly branches that
arise from nodes of the main stem. Spread by water
splash and favoured by moist conditions. Remove
and destroy all affected plants, select disease-free
planting material (Richardson and Merriman 1986).
Also crown gall (Agrobacterium sp.).
FUNGAL DISEASES
Anther smut (Ustilago violacea) was detected in
Qld in 1987 on a carnation crop grown from planting
material obtained from an approved source overseas.
Anther smut is an uncommon disease of modern
cultivars partly because very few produce anthers.
The disease has been eradicated (Bodman et al.
1996). The fungus is systemic and affected plants are
stunted, often producing excessive numbers of side
shoots. Purplish-black fungal spores replace the
pollen in anthers, flowers look dirty. Young plants
are very susceptible, infection can take place in buds,
cut stems and cuttings. Spores are spread by air
currents, water splash or by handling infected
material. Remove and burn infected plants (Com. of
Aust. 1991, Fletcher 1984).
A 16
ANNUALS AND HERBACEOUS PERENNIALS