Queensland, Australia
April 13, 2004
Farmers need to make sure their
winter cropping areas are free of host plants to reduce the risk
of crop damage from two recently discovered plant viruses.
Queensland Department of
Primary Industries plant pathologist Emma Colson said both
the wheat streak mosaic virus and the recently discovered high
plains virus were spread by the same insect, the leaf curl mite.
She said this meant that eradicating host plants would help stop
the spread of both viruses.
Dr Colson said the viruses could survive on volunteer plants of
wheat and summer cereals, cereal plants such as maize and host
grass weed species.
"Sorghum is considered a host plant in the United States and
DPI&F research later this year will determine whether this is so
in Australia."
She said virus management should involve:
-
spraying
out or cultivating green summer crop stubble and grass weed
hosts at least two weeks before planting wheat
-
controlling
volunteer winter cereal plants during fallow
-
controlling
grasses in fallow
-
controlling
grass weeds on crop borders.
Spraying mites with pesticides did
not effectively control them.
Dr Colson said the high plains virus was a relatively new
disease of cereals, first discovered in 1993 in maize and wheat
crops on the High Plains of the United States.
It was thought to be widespread throughout the world but had
been undiagnosed because of the complexity of developing an
appropriate test. The DPI&F virology laboratory had developed a
test with financial support from Plant Health Australia.
She said host plants included maize, wheat, barley, oats, rye
and some grasses.
Symptoms were stunting and yellowing, and mosaic patterning on
the leaves of infected plants.
Dr Colson said leaf curl mites carried the virus from infected
plants to healthy plants, travelling by wind and on clothing,
animals and vehicles.
She said mites needed a continuous "green bridge" of alternative
host plants to survive between crops. Removing all host plants
for at least two weeks between crops could disrupt their life
cycle.
Dr Colson said the commercial importance of high plains virus in
Australia was not yet known.
"We believe its effects will be similar to those of wheat streak
mosaic virus that caused some yield loss in a small part of the
wheat crop on one of the two commercial properties on which it
was found.
"Losses were minimal in the other commercial crops around
Australia where wheat streak mosaic was found."
She said testing was continuing on other plant material for high
plains virus, including any that had shown symptoms of wheat
streak mosaic virus last year but which previously tested
negative for that disease.
The DPI &F will soon be posting information on wheat streak
mosaic virus and high plains virus to all Queensland wheat
growers. Information is also available from the DPI Call Centre
(13 25 23) and from the DPI
website. |