Systemic iron implants alleviate symptoms of Mundulla Yellows in roadside eucalypts in south east South Australia
Mundulla Yellows is a dieback disorder of trees (predominantly eucalypts) along roadsides in the southeast of South Australia, characterized by interveinal yellowing of leaves and eventual death. There are two main theories about the cause of Mundulla Yellows: (1) that the yellowing is lime chlorosis, caused by crushed limestone dust from roads being washed into soil, and (2) that it is caused by an irreversible and transmissible biotic pathogen. We tested the lime chlorosis hypothesis by inserting nutrients directly into the sapwood of symptomatic trees using systemic nutrient implants. If the lime chlorosis hypothesis is correct, nutrient injections of iron and manganese should increase chlorophyll synthesis and result in leaves becoming greener. We applied four different nutrient combinations (iron, manganese, iron + manganese, and a treatment that included a range of essential plant nutrients), as well as control treatments, to symptomatic trees across 10 sites. After 14 weeks there were significant increases in leaf greenness and crown health, compared to controls, when trees received either iron or iron and manganese implants. The results add further weight to the lime chlorosis hypothesis. Nutrient implants are unlikely to be a viable management strategy due to their cost and potentially short-term benefits, and trees will inevitably be lost from the region’s roadsides. Management options should involve increasing revegetation efforts and natural passive regeneration of trees away from affected roadsides, and revegetating the affected areas with species that are suited to the changed soil conditions.
KeywordsDieback Lime chlorosis Nutrient deficiency Mundulla Yellows
Thanks to Ashley Olsen for his assistance in the field, including his photography. We would like to thank the following volunteers for the time they dedicated to scoring photographs: Emily Matthews, Phuong Doan, Michael Woodland, Sarah Box, Eleanor Fox, Patrick Piggott, Corrine Duncan, Rashedul Islam, Sandra Weller, Kristal Kinnane, Ramyaroopan Sewgolam, Freja Butler, Josh Matthews, Georgina Gould-Hardwick, Patrick Gregurke, Greg Horrocks, Gillian Armstrong, Naomi Menzel and Adrian Petrovich. Thanks to the Coorong and Tatiara District Local Action Plan committee, and in particular Graham Gates and Tracey Strugnell, for support, funding, and for helping us locate suitable sites. Thanks to Josie Jackson for sharing her considerable local knowledge. Comments from two anonymous reviewers helped to improve the manuscript considerably.
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