A new Poinsettia powdery mildew
There have been a number of interceptions (during 2001, 2002 - and now
2003 as well) on production nurseries of a damaging new powdery mildew
- American poinsettia powdery mildew (Erysiphe euphorbiicola)
Click here for pictures
Growers are advised to inspect plants for evidence of powdery mildew and
to contact their local PHSI if they have any
concerns. It is possible that the mildew could become established on wild
Euphorbia so any other Euphorbiaceae on the nursery or growing
as weeds should also be inspected.
This powdery mildew was first reported in Mexico in 1998 and was also
found in Puerto Rico at about the same time. It was later found in the
USA in 1990 where it has become a serious and widespread problem.
The American poinsettia powdery mildew produces powdery colonies
on both leaf surfaces. In the USA the disease often remains unnoticed
until late in the season when bracts are beginning to colour. Earlier
in the season, it may remain undetected because colonies mostly occur
on the under surface of the older, lower leaves.
The fungus produces large numbers of dry, powdery spores that are easily
dislodged by disturbance and dispersed by air currents. Spacing plants
well apart and having good air circulation can help control this disease
by reducing humidity within the plant canopy . To reduce the risk of spreading
the fungus from infected to clean areas strict hygiene measures
should be enforced. The spores are air-borne and it is likely that they
will survive on clothing for some time. To avoid cross-contamination it
is recommended that access by visitors is restricted and any personnel
visiting or working in Poinsettia houses should wear disposable boiler-suits
(e.g. Tyvek suits). In addition disinfectant foot dips should be installed
at doorways as a precautionary measure (e.g. Virkon, Jet 5 etc. are suitable
disinfectants).
Page last modified:
26 Oct 2006
Page published: 21 Jul 2003