Mango twig tip dieback

Region: Greater Darwin, Katherine Region | Topic: Horticulture
Nov 2021

Background

Since mid-2017, different symptoms of mango dieback have been observed in 15 orchards in the Litchfield municipality in the Northern Territory (Fig. 1). It is likely this disorder may be present in many more mango orchards. It was named mango twig tip dieback (TTD) to distinguish it from the common branch/twig dieback.

Severity can vary from orchard to orchard with some orchards badly affected. Plant stress does not appear to be a condition for TTD to occur as it has been seen in an orchard with otherwise very healthy tree canopies. It was also observed in an orchard abandoned a few years previously. TTD can also affect young trees, less than one year old, and the Kensington Pride (KP) cultivar is very susceptible.

Attempts to determine the cause or aetiology of TTD have been made. No particular insect has been associated with TTD and tests for Phytoplasmas were negative. To date, 150 fungal and bacterial cultures were isolated from 22 mango samples. One species of bacteria and 33 species of fungi (belonging to 23 genera) were found to be associated with TTD. No exotic plant pathogens have been detected. Two pathogenicity trials were undertaken to determine if some of the identified microorganisms were the cause, but TTD symptoms were not reproduced on the inoculated seedlings.

Map of the Northern Territory showing locations of known mango orchards affected by mango twig tip dieback

Fig 1: Geographical distribution of known mango orchards affected by mango twig tip dieback in the Northern Territory (green circles). Scale bar = 40km

Symptoms

Symptoms include a black longitudinal lesion on the last twig flush (above the last node) but only on one side of the twig. The lesion progresses both downwards and upwards, killing the apical bud. All leaves in the last flush become dried but remain attached to the twig (at least for a while). Sometimes, dried leaves can be seen only on one side of the apical bud. Sometimes, the second last flush and even the third last flush show the black lesion, with or without gum exudation. Most lesions appear to originate from the middle of the twig (between two nodes or between the apical bud and the last node).

Internally, the lesion sometimes extends for a few centimetres beyond the external symptoms. Transversal cuts of the twig show that the lesion is not in the middle but toward the external part. This causes the death of the twig (Fig 2).

Mango leavesDeformed mango leaves

Dead mango leavesInside branch of affected tree

Fig 2: Symptoms of mango twig tip dieback on a mango flush

The Department of Industry, Tourism and Trade will continue studying this disorder, with the support of NT Farmers and the NT Mango Industry Association, and would like to know how many more Territory growers are experiencing TTD in their mango orchards

More information

For more information email plant.pathology@nt.gov.au or phone 08 8999 2218.

Back to NT Rural Review - November 2021