Biological Control of Blackberry with Blackberry Leaf Rust Fungus
Note number: LC0143
Published: November 1999
Reviewed: September 2007
Common and scientific names
Common and scientific names Blackberry leaf rust fungus; blackberry rust Phragmidium violaceum (Schultz) Winter
 |
 |
| Figure 1. Blackberry leaves with golden summer spores ofblackberry leaf rust. | Figure 2. Black over-wintering spores of blackberry leaf rust. |
Background
European blackberry is a spiny bramble covering millions of hectares of bush and farm land in temperate regions of Australia with an annual rainfall of 750 mm or more.
The botanical name of European blackberry, Rubus fruticosus L. aggregate, indicates a number of closely related species which for convenience are dealt with (aggregated) under one name. In reality, there are at least seven species and a number of hybrids occurring in
Victoria. Most European blackberry species in Australia appear to exist as single clones.
Blackberry is a Regionally Controlled Weed in all Catchment and Land Protection Regions in Victoria except Mallee. Land owners in areas where blackberry is Regionally Controlled must take all reasonable steps to control it and prevent its spread on their land and the roadsides which adjoin their land.
Blackberry growth pattern
 |
| Figure 3. Blackberry growth pattern. |
Blackberry has a two year growth pattern. First year canes emerge from the root crowns in spring and grow quickly to the top of the existing canopy, eventually arching towards the ground (Figure 3). Having reached the ground, these canes produce buds and roots at their tips (daughter plants) in autumn, which lie dormant over winter. In the following spring, the daughter plants become crowns and sprout new canes.
Every spring, flowering canes grow in the axils of the old leaves of those canes which have overwintered (second year canes), producing flowers, fruit and seed. In winter, the second year canes die back to the crown, leaving independent daughter plants. A blackberry bramble consists of live first and second year canes plus dead material from previous years.
Origin of blackberry leaf rust
The blackberry leaf rust fungus is a very specific natural enemy of blackberry. It is commonly found where blackberry originates, throughout Europe, North Africa and the Middle East. Studies were undertaken in Europe in the early 1980s to assess its safety for use as a biological control agent in Australia. This research demonstrated that Phragmidium violaceum is specific to the European blackberry and does not damage native species of Rubus or varieties of commercial raspberry and brambleberry such as loganberry and youngberry, but could damage some varieties of thornless blackberry which are hybrids of the European blackberry.
Permission was sought to introduce a number of more highly damaging strains of the rust to Australia, but in 1984 the project came to an abrupt halt when the rust was discovered as an illegal introduction in southern Victoria. The “illegal” rust spread quickly throughout south-eastern Australia. Subsequent studies have shown that it is far less damaging to the predominant blackberry species in south- eastern Australia than the strains first selected in Europe.
Permission to introduce the more damaging strains was rejected in 1986 because of objections from people who considered blackberry useful. In August 1990 the Australian Quarantine and Inspection Service allowed Victorian scientists to release one of the damaging strains, which had been kept frozen in Europe since 1983.
Description
Blackberry leaf rust fungus is a defoliating disease which attacks the leaves and is also found on flower buds, unripe fruit and the green parts of growing canes.
The rust appears as characteristic purple-brown blotches, 2 to 3 mm in diameter, on the upper surface of the leaf (Figs.1 and 2). Corresponding yellow or black powdery pustules of spores appear on the lower surface of the leaf. Heavily infected leaves turn brown, shrivel and fall from the canes.
Life cycle
 |
| Figure 4. Life cycle of blackberry leaf rust. |
The rust undergoes a sexual cycle on new blackberry leaves in spring involving three spore types (Fig. 4). The golden summer spores first appear in early November, have several generations on young leaves and reach epidemic level by flowering time. Summer spores germinate in the presence of moisture and infect the blackberry when the germ tube enters the leaf through the stomata (breathing pores), found only on the lower surfaceof blackberry leaves. Leaf age affects the level of infection, with the most susceptible leaves being the youngest, fully opened leaves at the cane tips.
Summer spores are microscopic and carried by air currents, spreading the infection to other leaves, canes and plants. They have a generation time of 8 to 10 days. In late summer and throughout autumn, the pustules produceblack, sticky, over-wintering spores. These remain attached to any remaining leaves on the brambles and, when mature, are responsible for starting the next cycle of rusting on new spring leaves.
Other fungal diseases of blackberry
The blackberry leaf rust can be confused with three other fungal diseases of blackberry.
Blackberry orange rust (Kuehneola uredinis)
This rust has been in Australia since at least the early 1940s. It appears on the lower surface of the leaf as small powdery, orange pustules, the size of a pin-point. These do not have a corresponding purple blotch on the uppersurface of the leaf. Blackberry orange rust attacks the older leaves of blackberry in late summer and autumn and often creates larger powdery, orange pustules up to 1 cm long that can break through the bark of second year canes.
Septoria leaf spot (Septoria rubi)
This fungus appears as purple-brown blotches 1 to 2 mm in diameter on the upper surface of the leaf. The blotches sometimes have a white centre. There is never a corresponding yellow or black powdery pustule on the lower surface of the leaf.
Cercospora leaf spot (Cercospora rubi)
This fungus appears as brownish blotches 5 to 7 mm in diameter on the upper surface of the leaf. The blotches sometimes have a purple fringe but never a corresponding yellow or black, powdery pustule on the leaf underside.
Releases
One selected strain of the blackberry leaf rust, F15, that was known to be highly damaging to the predominant blackberry species, Rubus discolor, was released as a biological control agent in all Australian States in the summers of 1991 and 1992. Monitoring of its dispersal was complicated by the presence of the illegal strain.
Impact
 |
| Figure 5. Rust on blackberry in summer. |
 |
| Figure 6. Blackberry leaves that are severely attacked by the rust curl up and drop off. |
 |
| Figure 7. Defoliated blackberry in autumn. |
 |
| Figure 8. Blackberry infestation weakened by blackberry rust showing native plants growing through the blackberry. |
Blackberry leaves that are heavily infected with blackberry leaf rust turn brown, shrivel, and fall from the canes. The blackberry is forced to grow new leaves which in turn are attacked by the rust. Repeated defoliation weakens theplant which must then use up reserves stored in its root system.
Data from the two long-term monitoring sites in Gippsland shows steady reductions in blackberry biomass, decreases in the lengths of canes and dramatic reduction in the production of daughter plants due to rust infection. A reduction in total biomass of 56% for Rubus polyanthemus over 12 years and 38% for R. leucostachys over 8 years has been recorded. Production of daughter plants by R. polyanthemus has been reduced by 96%.
The rust causes extensive leaf-loss (Fig. 7) and can defoliate blackberry in summer and autumn. Defoliation of blackberry did not occur before release of the rust, but now occurs to a varying extent in summer every year. More light is able to penetrate through blackberry thickets, enabling other plant species to germinate and grow up through them. This change has been a slow, gradual process but canopies of blackberry, formerly fully closed, are now much more open. On agricultural land, the mainadvantage of the rust is that it has restricted the invasion of new land by established blackberry infestations.
Rust spores require high humidity to germinate so blackberry rust is more effective in the higher rainfall areas south of the Dividing Range in south-eastern Australia. The impact of the rust in drier areas appears mostly to have been minor and patchy.
In some cases the rust has taken several years to weaken well established blackberry but over time it has decreasedthe extent of existing infestations, slowed down the invasion of new areas and made the susceptible blackberry species less competitive with desirable vegetation.
In the long term, species of blackberry that are resistant to the rust have greater comparative fitness and are likely to proliferate. Resistant blackberry species may become more widespread and problematic. Research is in progress on the complex taxonomy of the blackberry aggregate and the susceptibility of the various species and hybrids to blackberry rust. New strains of rust may be introduced in the future to tackle blackberry that is rust resistant. Investigations are also in progess on the environmental factors which may be limiting the distribution and effectiveness of the rust and the potential of other management techniques to enhance rust impact.
Blackberry that is not attacked by the rust in summer and autumn should be assumed to be resistant and should be controlled by other means.
Integrated control
Biological control cannot totally eradicate a weed but can reduce the spread and density of infestations. In few cases is control achieved to the level where the weed is no longer of concern and no other control is necessary. More commonly, other methods are still required to achieve the desired level of control. Biological control should be used in conjunction with cultural and chemical control measures in an integrated management plan. Herbicide trials have shown that lightly to moderately rust-affected blackberries are controlled to the same degree as non-rusted plants. Regrowth from blackberries slashed in summer is very susceptible to rust attack.
Further information
Information on the identification and control of blackberry is available in the Landcare Note LC0188: Blackberry. For further information on blackberry management see The Blackberry Management Handbook or contact your local NRE Catchment and Agricultural Services staff.
For further information on the biological control of blackberry contact:
Keith Turnbull Research Institute,
PO Box 48, Frankston, Victoria, 3199.
Tel: (03) 9785 0111 Fax: (03) 9785 2007
Email: ktri@nre.vic.gov.au
References
Bruzzese, E. and Lane, M. (1996) The Blackberry Management Handbook. Melbourne, Department of Conservation and Natural Resources.
Bruzzese, E., McLaren, D. and Grace, B.(1996) Biological Control of Blackberry - An Update. Frankston, Keith Turnbull Research Institute.
Groves, R.H., Williams, J. and Corey, S. (Eds.) (1998) Towards an integrated management system for blackberry (Rubus fruticosus L. agg.). Proceedings of a Workshop held at Charles Sturt University, Albury, New South Wales on December 15-16 1997. Plant Protection Quarterly 13(4), 151-199.
Parsons, W.T. and Cuthbertson, E.G. (1992) Noxious Weeds of Australia. Melbourne, Inkata Press.
Pritchard, G. (1990) Control of rust-infected blackberry with herbicides in Victoria. Proceedings of the 9th Australian Weeds Conference, Adelaide, August 6-10.
Acknowledgements
This Information Notes was developed by Keith Turnbull Research Institute, Frankston.
Prepared by El Bruzzese and Anne-Marie Tenni, June 1992. Revised by Ian Faithfull, November 1999.
Biological control of blackberry is funded by NRE and the Cooperative Research Centre for Weed Management Systems.
