Blackberry control manual - Weeds Australia

The rust usually appears as characteristic
purple‐brown blotches, 2 – 3 millimetres in
diameter, on the upper surface of the leaf.
Corresponding golden or black pustules, or small
blisters from which the spores emerge, appear
on the lower surface of the leaf. Heavily infected
leaves turn brown, shrivel and fall from the
canes.
Rust spores require dew, rain or high humidity
to germinate. Infection levels are greatest when
blackberry is actively growing and a large
proportion of the plant canopy is young leaves.
Localities where the annual rainfall is greater
than 750 millimetres and evenly spread over
the full year, and the average daily temperature
for January is about 20 ºC, have been found
to be optimal for this rust species. Therefore,
blackberry rust is more effective in the higher
rainfall areas south of the Dividing Range in
south-east Australia. The impact of the rust in
drier areas appears to have been mostly minor
and patchy. The rust may perform well in lower
rainfall areas if humidity is higher, such as near
irrigation channels or in riparian zones.
The strategy being implemented to facilitate the
spread of the new strains of the fungus recently
introduced to Australia is to release them at a
range of sites across Australia to help the natural
spread of the agent. It is well documented that
the rust can spread over long distances. The
new strains may become established, build up
and hybridise with the existing rust populations,
and better rust genotypes could emerge. The
better genotypes that emerge will enhance the
biological control of blackberry at some sites and
eventually will spread to other infestations.
lower surface of the blackberry leaf. Summer
spores are microscopic and are carried by air
currents, spreading the infection to other leaves,
canes and plants. They have a generation time of
8– 10 days under optimal conditions.
In late summer and throughout autumn, the
pustules produce black, sticky, over-wintering
spores. These remain attached to leaves that fall
off or remain on the blackberry during the winter
and are dormant until the next growing season.
They are responsible for starting the next cycle
of rusting infection on new spring leaves.
Leaf age affects the level of infection; the most
susceptible leaves are the young, fully opened
leaves at the cane tips.
The blackberry leaf rust fungus (Phragmidium violaceum).
CSIRO Entomology
Life cycle of the blackberry leaf rust
fungus
There are five separate spore stages in the life
cycle of the rust.
The two commonly seen stages are the golden
powdery summer spores (urediniospores)
and the sticky, black, mostly winter spores
(teliospores).
The golden summer spores first appear in
late spring following the emergence of new
primocanes and have several generations on
young leaves. Summer spores germinate in the
presence of moisture. They infect the blackberry
when the germ tube enters the leaf through the
stomata (breathing pores), found only on the
Blackberry leaf rust fungus. Heavily infected leaves turn
brown, shrivel and fall from the canes.
CSIRO Entomology
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