PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
HEMI-
PARASITES
(contd)
Not usually economically
important but smothers
smaller native plants in
bush areas, mainly a
problem in bushland
DEVIL'S TWINE, DODDER LAUREL (Cassytha spp., Lauraceae)
Has chlorophyll.
No true roots. Depend on their hosts for water and some nutrients.
Straggly perennial climber, stems generally green, or yellowish- green.
Leaves scale-like. Flowers small and white. Parasitic on stems of mainly
woody plants, eg wattles. Do not confuse with dodder (Cuscuta spp.).
Spread. Seed is spread by birds. Seedlings climb up nearby hosts, roots die
after contact is made with the host, severing connection with the soil.
Smothers hosts and causes general debilitation. In exceptional
circumstances kills the host. Infestations are rarely economic in crop plants.
PhotoCIT, Canberra
(P.W.Unger).
TRUE
PARASITES
Do not confuse
True parasites lack chlorophyll and have no true roots, depend entirely on
their host plants for food and water. Some are native, others are introduced.
DODDERS (Cuscuta spp., Convolvulaceae)
Have no chlorophyll.
No true roots.
Straggly annual climber. Distinctive fine leafless, yellow or brown, wiry
stems, can twine around herbaceous plants completely covering the host.
Flowers are small cream or white clusters produced in summer. Host crops
include lucerne, red clover, vegetables, eg carrots, onion, annual ornamentals,
eg aster, weeds, eg skeleton weed. Host range can vary depending on species.
One dodder plant can spread up to 2 meters in diameter.
Spread by contaminated seed, hay, harvesting machinery, running water or
in manure. As many as 3000 seeds may be produced by a single plant. Seeds
can germinate in the soil immediately or remain dormant for 20 years.
Seedlings climbs up any nearby host, then sever their connection with soil.
Infestations reduce yield and may kill crops.
May spread virus diseases of the host plants.
Thin yellowish dodder
stems on calendula
seedlings in a punnet.
PhotoCIT, Canberra
(P.W.Unger).
Parasitic flowering plants 381