Parasitic plant: Scurrula parasitica
Why is it a problem? This parasitic plant can reduce growth and vigour of citrus trees. It is easily managed, and only causes serious problems in neglected orchards.
Where and when is it a problem? It occurs in all citrus growing areas from 500 to 1800 m asl.
Leaves are roundish and somewhat leathery with a silvery grey appearance due to the whitish down on their underside. It flowers in July/August. Flowers are 3 cm long, curved, red at the base and greenish yellow near the tip. The berries are small (6-7 mm long), red when ripe and has extremely sticky flesh.
Infested trees may have many parasitic Loranthus plants growing on it. Heavily infested trees have reduced growth. In grossly neglected orchards and under drought stress it can result in dieback of branches and occasionally the whole tree.
Confusion with other pests: This is the only parasitic plant on citrus. A closely related species, S elata, can be parasitic on apple and peach trees. S. parasitica occurs at lower altitudes (500-1800 masl) than S. elata (above 2200 masl).
Lifecycle: Seeds germinate and sink parasitic haustorium (an attachment mechanism) into the branches of their host. Later, secondary haustoria are formed from the same parasitic plant wherever there is a contact with the host.
Dispersal: Birds, after eating the berries, either excrete or wipe off the seeds from their bills onto the branches of neighbouring plants.
When can damage be expected? Serious problems are only seen in grossly neglected orchards.
Hosts: It parasitizes shoots of trees and shrubs.
This parasitic plant is easily managed, and should never become a problem in well managed orchards.
Inspect for loranthus during general orchard monitoring and when pruning.
Effect of variety
- Prune infested branches to remove loranthus
- All wood that is infested should be removed as the parasites’ hautoria are deep-rooted and can cause new growths.
- When removing loranthus from heavily infested trees the tree usually does not fruit in the first year after pruning, but should start fruiting again after that.
- Recovery of trees can be stimulated by proper management like manuring and irrigation.
- Keeping other host plants (forest and fruit) surrounding the orchard clean of loranthus may also help reduce the risk of spread into the orchard.
Chemicals are not necessary for managing this plant.
Image acknowledgements: NPPC.