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Afrikaanse Inligting
Witches Broom - A Conebush Disaster
The Agricultural Research Council Fynbos has suspended the sale of all Conebush cuttings to the cut flower trade industry because of two new diseases. These are (from SAPPEX News 104: 6-7):
Yellow Leaf Blotch.
A yellow discoloring on veins of young leaves that matures into little rectangular
lesions, thought to be caused by a virus. At first it can be confused with a nutrient
deficiency. It seems to spread rapidly even on sterilized pruning shears. Any plants
(especially the cultivars Rosette and Safari Sunset) brought from Elsenberg
during 1998-9 may be infected. A mild form was seen on Pr susannae at
Elsenberg as well.
Witches’ Broom
When atlassers recorded Witches’ Broom in our survey of Witches’ Broom for Rose
Newton (PAN 31.11 - are you still remembering to record this when you see it?) on
Conebushes and other plants it was poo-pooed as spurious – "Witches’ Broom
only occurs on proteas". Now it is a serious problem on Conebushes. Initial tests
suggest that the symptoms are associated with a mite similar to the Protea Witches’
Broom Mite Aceria proteae, but that (as atlassers noted!)* the symptoms are
not full broom, but more a miniaturization or bonsai effect. It is now a major problem on
most cultivars - "in almost all Jubilee Crown, Pisa and Chameleon fields
and also in Inca Gold" (bold emphasis inserted). The problem has also surfaced in
the Northern Hemisphere. It seems to be spread by both aphids and pruning shears.
We hope that this is a temporary inconvenience to the industry – more importantly to the development of new cultivars. It will certainly mean that many growers will have to prematurely replace their orchards. But what will they be replaced with? Elsenberg is trying to determine the causative agents, although I find the attitude - that "… the search for a cure cannot begin" … "until it is known what the cause is …" - to be both short sighted and ridiculous. Experimenting with acaricides and pruning hygiene may well yield a cure to the problem before the causative agents are discovered. Given that all Conebush distribution has ceased, with growers potentially losing large orchards, surely the expense is justified? Tony
*Atlassers even recorded Witches Broom on a Needlebush. A 4m tall Ha sericea plant near Paarl had half the bush stunted with 3mm-long needles in dense, broom-like growths. Unfortunately, this plant was cleared for a fruit orchard in 1998. Rose could not find any mites in the broom at the time.
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