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© ICFR 2017

Environmental triggers and impact assessment of a new rust disease caused by

Uromycladium acaciae on black wattle in South Africa

Thobile Nxumalo, Ilaria Germishuizen and Andrew MorrisForest Science Symposium-18-20 July 2017

© ICFR 2017

Background (Acacia mearnsii)

Acacia mearnsii De Wild (black wattle) is one of the importantplantation species in South Africa (SA)

It is native in Australia and grown in SA for timber and tanninproduction (Searl,1991)

Black wattle occupies about 110 000ha of plantation area out of1.3M ha of planted forests

85% of the revenue is from timber and the other 15% from bark(Chan et al. 2015)

Therefore, it is economically important plantation species and anyrisk factors needs to be managed

Searl S. 1991. The rise and demise of the black wattle bark industry in Australia. Technical paper no. 1. Canberra: CSIRO Division of Forestry

Smith CW. 2002. Growth and yield prediction. In: Dunlop RW, MacLennan LA (eds), Black wattle: the South African research experience.Pietermaritzburg: Institute for commercial Forestry Research. P93-99

Background (risk factors)

Few pests and disease have been reported on black wattle inSouth Africa such as:

Currently, is the new Uromycladium acaciae which is causingdisease on Acacia mearnsii

Photo by Benice Sivparsad

Species distribution

• Nine species of Uromycladium infect Australian acacias• All Uromycladium species are autoecious (Fraser et al. 2017)• Three have been described in the country

• U tepperianum (Morris, 1987)• U. alpinum (Morris and Wingfield, 1988)• U. acaciae (McTaggart et al. 2015)

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Uromycladium acaciae life cycle

Dr Stuart Fraser, 2017

TeliaTeliospores

Spermogonia

Basidiospores

© ICFR 2017

Background and Objectives

Due to the disease outbreak, a multi-faceted project wasinitiated to manage the pathogen- integrated approach

IPM, defines economic injury levels, it developspreventative management and monitoring systems thatwill allow curative control measures are economical andenvironmentally sustainableBiology (taxonomy, epidemiology and

population dynamics) of the pathogen

(ICFR & FABI)

Monitoring sitesMonitoring the disease outbreaks

(ICFR, NCT & FABI)

Wattle rust exclusion plot trialsQuantify growth impacts

(ICFR,NMMU & FABI)

Monitoring sitesRemote sensing work

(ICFR, NCT,FABI & UKZN)

Relate the levels of infestations to environmental factors and identify triggers of outbreaks; and

Provide ground-truthing points for developing a remote sensing based system for detecting and monitoring wattle rust

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• Disease severity increased even with minimal amount of rainfall

• Disease severity increased around March- April in all the site type classes with the exception of two sites in the warm-wet site where the symptoms were observed earlier

• No major differences in RH were observed during the study.

• Temperatures between 18 -25 °C had an effect on disease severity

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KZN-weather data- (slide provided by Dr Stuart Fraser)

Based on the preliminary work done at FABI, March and October months have conducive weather for Uromycladium acaciae• Night time temperature averages

12-17°C• Evening rainfall and fog – wet

conditions overnight

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Results

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Comparing mean DS in MPU areas

Mool(a) Zoonstr norm

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Comparing mean DS in KZN areas

Baynes HC Bloem

• The decrease in disease severity in Baynesfield maybe the high infestation of mirid damage on the site

© ICFR 2017

Conclusion

The study showed that disease spread or severity is driven by moisture and temperature

Rainfall and temperatures between 18 and 25 °C can trigger the disease infection

The data will be used to develop a bioclimatic risk model to evaluate the geographic extent of the disease and potential hotspots

© ICFR 2017

Acknowledgements

Dr Kabir Peerbay (ICFR), Craig Norris (NCT), Johan Nel (TWK), Prof Jolanda Roux (SAPPI), Dr Alistar McTaggart (FABI),Dr Stuart Fraser (FABI)

Forest Protection Technical team (ICFR)

Marilyn Bezuidenhout and Enos Ngubo

Hardus Hatting (contractor in Piet Retief)