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Mundulla Yellows - A Simple Case of Poisoning

James A. McNamara


Trees and associated vegetation expressing a range of symptoms termed 'Mundulla Yellows', are readily found in the settled areas of South Australia. Critical observation of the ground beneath such plants indicates the presence of residual herbicide within their putative root zone.

Routine use of root absorbed plant poisons is observable and documentation of some practice is recorded here. Both in the practice of public utilities and private usage, knock-down and residual plant poisons are often applied, in combination, at least once a year. This is usually described as pre-emergence weed control and in the categories considered here usually takes the form of 'total weed control', wherein, residual herbicides are applied at the highest rates with the aim of stopping all weed growth, that is, killing all plants on certain patches or strips of ground.

Documentation confirms the historical and current use of particular common combinations of plant poisons: amitrole with atrazine and glyphosate with simazine, by highways, water and local government authorities, to kill plants along unsealed shoulders of roads, around roadside furniture and water meters and indicator posts, near intersections and railway crossings, on drainage structures and along drains and so on. Atrazine and simazine are root absorbed plant poisons and in the case of simazine the manufacturer's cautions leave no doubt as to its danger to 'off target' species through the action of the roots.

The triazine herbicides are the most likely candidate class of plant poisons, through their pattern of use and symptoms caused. The explanatory power and simplicity of the herbicide hypothesis suggests that it should be favoured unless or until it is shown to be inadequate.

Field study relates disease to tree size and distance from a 'total weed control kill zone' (DKZ). A good working hypothesis is, that intolerant susceptible trees will be affected when and wherever such poisons are applied to soil within reach of their roots. A variable distance, a maximum DKZ (MDKZ) is easily measurable for each situation. In the case of the Booloman-minga, Eucalyptus porosa, this distance is about 16 metres.

The basic epidemiology of this disease, associates it markedly with certain artificial landscape features: roads, rails, drains, gravel paths, driveways and car-parks, and in more urban areas, brick-paved and gravelled street-scapes, places where total weed control is often manifest.

Not all weed control is total, it may be partial as in the elimination of broadleaf weeds from grassed areas. These may be viewed in the same way, however, and DKZ or MDKZ distances measured. In this way a disease zone may be defined round golf-course fairways, ovals or lawn tennis-courts etc.

Nothing of the epidemiology presented so far suggests an infectious biotic pathogen is necessarily implicated in the primary causation of the burgeoning Mundulla Yellows epidemic.

In the face of unchanging practices of herbicide use the prognosis is: the loss of all susceptible trees within the appropriate distance (MDKZ). That is, all redgums near treated roadsides, railways and drains etc. will be lost throughout South Australia. The solution to the problem is simply to stop poisoning these desirable trees.

Key words: herbicide, tree, roots, disease, roadside, yellows, triazine.


In mid 1991, I discovered that the then Engineering and Water Supply Department (E& WS Dept.) had sprayed part of my property, the approaches and surrounds of a new water-meter, with a herbicide mixture. This was a shock to me. Up to that time I had no real understanding of what such routine maintenance practices involve. In both the practice of public utilities and in private usage, knock-down and residual plant poisons are often applied, in combination, on at least an annual basis. This comes under the heading of pre-emergence weed control.

Through looking at that initial incident, a body of common knowledge was revealed to me. A works manager suggested that their practice was rather mild and inoffensive, when compared with that of the highways or railways authorities. Informed observation has revealed much more, in the years since the initial insult, and bears repeating here.

First was a case involving my father's plum tree, in which the adjoining land was acquired by the Highways Department. Land which had been a flowerbed was thence forth maintained as a weed free gravelled surface. The tree yellowed on the closest side. Plant poison would have to have been applied to the ground within 0.5 m of the butt of that tree, to achieve the soil-sterility visible there.

Secondly a yate tree, Eucalyptus megacornuta, which I had grown from seed, was alongside a weedy neighbouring backyard for many years. This weedy area was then converted into a gravelled, weed-free carpark. The tree developed patchy yellowing. In this case poison would have to have been applied right to the butt itself.

Eucalyptus camaldulensis   
Fig. 1 A typical example, Eucalyptus camaldulensis, near a roadside. (MYS = 6, DKZ < 3)

Thirdly the District Council of Mallala started spraying the newly constructed Aqua Street drain, near my property, on 29 June 1994. This was repeated on 2 June 1995 and one annual treatment has been applied each year since, thus providing me with literally, an armchair view of this type of practice. It is easy to miss, just a few minutes in each year is all that is required to lay down a total weed control along a few hundred metres of drain. In this case a side-jet of glyphosate and simazine is applied from a moving vehicle, in one pass, except near culverts where two passes are made. (I do not know what two times total is, but presumably this makes sense to someone.) Timing of application is seasonal and succeeds the opening rains by a few weeks, this year it was 11 May 2000. The speed of this activity may account for the number of people I have spoken to who are quite unaware that it occurs in their area, including even life-long residents of farming background.

Concomitant with this initial period of passive observation was an absorptive process in which I gradually became aware of; what can now be described as an epidemic of yellowing, sickening and dying trees, chiefly on roadsides in this state and beyond. At some stage I started to use my own mnemonic appellation of 'Highways Department Yellows' for it.

'Mundulla Yellows' as such, entered my local area via the local newspaper, reporting on the Mundulla Yellows bandwagon, with Geoff Cotton and Kym Knight well to the fore of concerned and active citizens (The Bunyip, November 1999). Almost immediately this resulted in the destruction of a suspect tree. Supposedly infected, it was removed from a local schoolyard (The Bunyip, 10 November 1999: 7). This predictable knee-jerk reaction from the general public was one of the things, that I wish may be avoided. However, this stimulus from local publicity was sufficient to cause me to begin an active phase of enquiry.

What is Mundulla Yellows?

This question is adequately answered, for the purposes of discussion, by Hanold and Randles (1999) in their pamphlet with good colour photos and a description of symptoms which allow useful discussion of this particular suite of environmental concerns (those symptoms are all listed in Table 1). To underline that point, it is precisely those sick trees and associated vegetation figured or listed by the authorities (Hanold and Randles 1999, Paton 2000) and the several examples viewed during the course of the excursion included in the recent national conference, held in Adelaide (SASA/AIH 2000), that are the basis of our concern here. They are, by definition, Mundulla Yellows cases. The question then is, what is the cause? Unfortunately the act of naming a disease does allow a form of nominal fallacy to take hold. It is the one in which one is apt to assume that because it is a disease it is also of microbial origin and infectious, while these things may or may not be true. This has already happened, repeatedly, but I am getting ahead of myself.

Table 1. The symptoms of Mundulla Yellows and simazine poisoning
Scores are (+) observed, (-) not observed, and (na) not applicable. Columns are: MY symptoms from Hanold and Randles (1999), WF from simazine trials of Dalton and others, and PT the Polley tree treated with glyphosate and simazine in 6 annual doses.
Symptom MY WF PT
Interveinal yellowing + + +
Necrotic spotting + - +
Leaf distortion + + +
Shoot death + + +
Patchy crown + na +
Epicormic regrowth + na +
Suppressed reproduction + na +
Death + + na
MY = Mundulla Yellows, WF = Woods & Forests trials, PT = Polley Tree

My initial enquiries led me to make direct contact with many of the major players in this field including, David Paton, John Randles, John Choate, Geoff Cotton (co-discoverer and most seasoned campaigner) and many others. Rather than dampening my concerns these enquiries persuaded me that 'Mundulla Yellows' and my 'Highways Department Yellows' were closely comparable and could be sensibly viewed as expressions of the same roadside phenomenon. I say roadside phenomenon deliberately because that is still true, some twenty-odd years down the track (Paton 2000, Paton and Cutten 2000). This is especially so at the eponymous locality, near Mundulla, where, I am assured, there has been very little lateral spread, off the roadside, and where there has been some it was "on a watercourse and on the downstream side" (D.C. Paton pers. comm.).

The basic epidemiology of this disease or syndrome associates it markedly with certain landscape features including; roads, rails, drains, fence-lines; gravel paths, driveways and carparks and in more urban areas, brick-paved and gravelled streetscapes (pers. obs., Paton 2000).

The list of species affected is large and many dominant local trees are high up among the most susceptible. Darrell Kraehenbuehl (pers. comm.) lists Eucalyptus camaldulensis, E.leucoxylon. E.baxteri, E.viminalis, E.diversifolia and E.fasiculosa. I would add the box group, E.porosa - E.largiflorens. Hanold and Randles (1999) figure the popularly planted ironbark, E.sideroxylon, and sugargum, E.cladocalyx.

Eucalyptus porosa   
Fig. 2 Another roadside this time with a treated drain extending almost to fence-line. Right foreground specimen with inclined trunk, part of the Booloman-minga grove of Eucalyptus porosa, (MYS = 7.5, DKZ = 0).

The taxonomic spread of this yellowing disease is extremely wide. Field ecologists list other genera including, Acacia, Allocasuarina, Banksia, Adenanthos, Hakea, Melaleuca, Kunzea, Dampiera and Xanthorrhoea. Unrelated trees and shrubs may show the same symptoms in the same areas. Indeed as Paton and Cutten (2000) describe this effect, the sick plants are found along the same roadsides. They report finding sick Allocasuarina, Xanthorrhoea, Melaleuca, Bursaria, Dianella, and Acacia under sick eucalypts of five species. Please note here that we have two monocots among four different families of dicots in that short list. These workers were explicit in their view that this wide range of plant taxa were "showing symptoms of Mundulla Yellows". Clearly, used in this way the disease name adequately and truly encompasses the real scope of our concerns. Unfortunately, mention must be made of a recent attempt by one worker (F. Podger pers. comm., in an unpublished statement to the recent national conference, SASA/AIH 2000), to confine or restrict the use of the name to species of eucalypts only. At this early stage of rigorous investigation it is crucial that important epidemiological evidence, of other taxa, not be ignored.

The Practice

What is it about main roads, water meters and the other landscape features I have mentioned? Can at least some of this routine maintenance be documented?

In a letter dated 4 September 1991, the then Minister of Water Resources, the Hon. Susan Lenehan wrote, to the author:

"The department has for many years used agricultural chemicals in non-urban areas to control vegetation growth around its water meters, chambers and indicator posts. This is done to assist maintenance personnel in locating, operating and repairing these facilities and in some cases for fire protection. Low toxicity herbicides applied by trained operators using hand line are employed to minimise the area affected."

The same authority in a letter to the Hon. M. Elliott MLC, dated 20 November 1991, said:

"Until recently, [a] liquid herbicide has been used. The active constituents of this product are Atrazine and Amitrole, both at concentrations of 320 gms/litre. The former chemical provides residual control of new growth, the latter "knockdown" control of existing vegetation. Application rates used were as per the manufacturer's recommendations (1 in 100)."

She went on to say:

"[Now] a combination of [brand name] (Glyphosate 360) and [another brand name] (Simazine 500 gms/litre) has been adopted throughout the Metropolitan North Region for work of this type."

Much more recently the Minister for Transport, the Hon. Diana Laidlaw MLC, in a letter to the author dated 8 February 2000, states that:

  • "Herbicides may be used by Transport SA (formerly Highways Department in part) for a range of purposes including:
  • to control weed growth on unsealed shoulders as an alternative to mowing or grading;
  • to control vegetation growth around roadside furniture (such as signs, guard rail, median fencing and guideposts) to ensure visibility where accessibility limits the use of other methods;
  • to control vegetation growth in surface drains and around other drainage structures where accessibility limits the use of other methods to ensure that stormwater can flow unrestricted;
  • to maintain safe sight distances within the road reserve at junctions, intersections, railway crossings and areas of tight alignment; and
  • to control weed growth before and after planting or direct seeding on un-grassed medians.
Transport SA has advised that the residual herbicide [brand name of product containing amitrole and atrazine] was in general use for control of weed growth along unsealed shoulders and around roadside furniture up until about May 1996, when it was replaced by glyphosate and simazine." (My italics.)

My own district council of Mallala confirmed in recent correspondence to me, that they routinely use a mix of glyphosate and simazine along drains and in townships in their region. As their replies to letters, if and when they arrive, can be laconic almost to the point of obscurity, I will spare you an extensive quotation of my own letter which they graciously answered in the affirmative. Words apart, and like its fellows, this body has demonstrated its usual thoroughness in spraying most of the roadside and other drainage lines in the district. This has been carried out since mid May and at the time of writing (August 2000) the patches of weed death are at their most visible. This is the time of year to observe the distribution and extent of this type of weed control carried out by the above mentioned bodies as well as by other public and private entities. While nature provides a lush green mantle of weedy growth, man procures a patch or halo of yellowed sickness. (* see footnote)

The Chemicals

Let me refer to the label information relating to one of these chemicals - simazine, a triazine related to atrazine, and I quote directly from the product information sheet of one of the local suppliers (Nufarm 1997). Under the heading, "Mode of action", we find (my italics) "Simazine acts as a selective herbicide which is absorbed through the roots and is translocated through the xylem to the actively growing shoots and leaves." Throughout the text we find cautions, "DO NOT use on sandy or porous soils near desirable plants or trees or where roots of such may extend or are near the surface." "DO NOT use near newly planted shrubs, young ornamentals and species with shallow surface roots." "DO NOT use in channels or drains where roots of desirable plants or shrubs may be extended." Then under the heading of "Disposal" we find that containers must be buried "clear of waterways, vegetation and roots."

I think you will agree that if we heeded the manufacturers cautions, none of us would use this root absorbed plant poison on many of the sites currently being treated.

Eucalyptus camaldulensis   
Fig. 3 A highly intolerant specimen, Eucalyptus camaldulensis (MYS = 5, DKZ = 3.5), among more tolerant species. This is the Polley tree of the text and the child marks the centre of a drain given 6 annual treatments of simazine and glyphosate .

Eucalyptus camaldulensis
Fig. 4 Foliage of Eucalyptus camaldulensis, showing interveinal yellowing and necrotic spotting and distortion. This sample was clipped from panic growth on a limb of the Polley tree [above] and was part of a sample tested for simazine.


What symptoms can we expect in eucalypts, from triazine poisoning? Very few published reports give sufficient detail for our purposes. Sampson (1985) reported root adsorption and death of E.sargentii with simazine use. Dalton (1993) figures a sick and yellowed Acacia seedling in his book on revegetation. It was responding to simazine. Some public sector research in the field of revegetation is germane, notably that of Dalton and colleagues (Barron et al.1998, Dalton 1987, Dalton and Bulman 1985) which I interpret to provide part of Table 1. Sufficiently detailed descriptions of symptoms are unfortunately rare. Suggestive reports are more easily found as in the work of Hall (1985) or Nazer and Clark (1984) related more directly to acacias, or the anecdote of Jamieson (pers. comm.) in which drift of the triazine, hexazinone, produced almost identical foliar symptoms in E.botryoides.

The Chemicals in Use

Many people I have spoken to in preparing this piece have an anecdote directly relevant to this subject: from the row of mallees along a Conservation Park firebreak, poisoned with hexazinone (H.J. Eckert pers. comm., R.F. Brown pers. comm.), to the European box shrubs, yellowing and dying in soil soaked by the splash from a fountain in a small ornamental pond. The pond had been treated with simazine to kill algae (E. Kokoschko pers. comm.). These can give us a good feel for the subject and its many ramifications but what of other important details?

When did atrazine use start on our roadsides? Probably shortly after 1971, the year of its registration in South Australia, in its popular mixed formulation (the same brand name already deleted from the Ministers' letters above). This would have been almost certainly the timing within Transport SA - Highways Department, specifically too (B. Larkin pers. comm., W.J. Vaninetti pers. comm.), although this same product was reported in agricultural use in the late 1950s (Sampson 1985) and seems to have been used in Pinus radiata production in the 1960s (R. Boardman pers. comm.). Rates of application of 20 - 30 kg/ha have been used (ibid.). Increased pine productivity was obtained at these rates, well beyond those lethal to troublesome native plant competition. Sands and Zed (1979) discuss the use of 3 - 30 kg atrazine /ha, in this context and note that less than 2 kg/ha was lethal to weeds such as Eucalyptus and Acacia.

This raises the point of particular tolerance to herbicides shown by some plants, which is a well known feature of their action and indeed renders them useful at all. As well as Pinus, Callitris is noted for atrazine and simazine tolerance (Sampson 1985, Dalton 1993). In the same way olive tolerates simazine quite well and is one of the few trees to re-establish in treated areas (Elmore 1994, pers. obs.).

How much of this poison has been used? In the United States the National Academy of Science (1975) said that "7.7 million kg of herbicides are used every year by highway and utility crews to clear roadsides and right of ways". Pimentel et al. (1980) add that "damage to crops, gardens, treecrops and shelterbelts arising from such application is reported each year".

What are the relevant rates of application? The local National Parks and Wildlife Service, Weed Control Manual (Anon. ca. 1985) describes how residual herbicides are "used at higher rates for total weed control along fence lines or other areas where no vegetation is required". The word "higher" is used where "highest" may be more accurate when the matter is total kill off of vegetation. Although, as I noted in the case of the drain in front of my own home, it is possible for some patches of soil to receive double the total weed control amounts from one operator, to say nothing of subsequent applications of similar materials by other agencies or individuals.

Some of the chemical species of interest to me have had wide use in agriculture. Blum et al. (1993) report that for the year 1987, 11 million kg of atrazine were applied to the state of Nebraska. It is used under maize as that crop is tolerant, metabolising it rapidly to non-lethal metabolites. Non-lethal to maize that is.

This is not a review of herbicide use nor have I exhausted the full range of suspect chemical species relevant to this study. Mention should be made of the third triazine, hexazinone again because of its wide use and because I have reports both of its use for the purpose of killing eucalypt regrowth (H.J. Eckert pers. comm.) and that the symptoms it produces in eucalypt foliage are very closely comparable with those associated with Mundulla Yellows (G. Jamieson pers. comm.). Passing reference should also be made to another group of chemicals, the sulphonylureas, if for no other reason than, an experienced plant toxicologist thought that the list of Mundulla Yellows symptoms mimicked those of that group of plant poisons (C. Preston pers. comm.).

Other Factors

In relation to soils, a connection between some Mundulla Yellows symptoms and limey material, either naturally occurring or transported as road fill, has been noted (P. Bulman pers. comm., L. Oldrey pers. comm.). Longevity of herbicides is routinely measured in standard soils under standard conditions and these are the figures usually quoted. Many chemical species show increased persistence in soils as they dry and as alkalinity increases and associated biological activity decreases (R. Kookana pers. comm.).

For atrazine, text books quote a "persistence time" of active amounts in the range of 4 - 18 months, for this "non-selective" plant poison (Hance and Holly 1990). Tilbury reported (on ABC radio)a half-life for atrazine of 8 years; this was based on the work of Franzmann and others (1998), who said that atrazine has a half-life in soil on the Swan Coastal Plain (Western Australia) ranging from 1 - 8 years. Tilbury's co-supervisor, Prof. E.L. Ghisalberti reports a half-life of 5 - 7 years for the same molecule in certain Western Australian soils. One may suppose that these are non-standard soils.

There is a patchiness of effect, within the crown of the diseased tree, that needs to be accounted for (Hanold and Randles 1999, Paton and Cutten 2000). I would suggest that a root-absorbed plant poison may be applied to the soil over part only of a tree's root system, along a road, fence line or path etc.. So that an asymmetry of dose may translate into an asymmetry of toxic effect - through the agency of translocation through the xylem vessel system of the plant.

Tree Diagram

Our trees are adapted to Mediterranean climates in which most water usually arrives at the soil surface in the form of light winter showers. As a result they have strong and efficient surface root activity. My young (15 years) box trees (indigenous to the Gawler River floodplain) are capable of drying the soil surface, visibly, within a 10 metre radius of their butts, in a day (24 hours), following rain. The diagram at left illustrates this general point using the example of the olive, a typical Mediterranean tree. The figure is marked with a point 'P' so that we may more easily consider the result of applying a residual poison in such a position every winter, as it would be if this were a roadside or one of the other landscape features already mentioned. Why should this tree not show signs or symptoms of poisoning?

Towards an Hypothesis

The symptoms one might expect from both atrazine and simazine poisoning, arise from root absorption, translocation to growing tips where interveinal yellowing, necrotic spotting etc. may occur, leading to failure of flush growth. While these symptoms are not unique nor necessarily exclusively diagnostic, the accordance is at least highly suggestive (see Table 1.).

The known mode of action and high probability of repeated soil-mediated dosing, suggests a most likely and easily testable hypothesis, for the root causation of Mundulla Yellows. That is, that most of these trees have been poisoned.

The process suggested here, is soil to root with translocation to shoot producing shoot failure. All of which is repeated leading to the death of the tree under the stress of persistent and/or continual insult or injury. To make it quite clear I must point out that I am talking about root causes not secondary or tertiary effects. That is, effects subsequent or subordinate to a significant environmental stress. I wish to avoid the fate, of somewhere down the track, hearing myself accused of having been barking up the wrong tree.


Tests in the three areas, soil chemistry, leaf chemistry and tree distribution, were attempted with limited time and no research budget in the period prior to the national conference.

Soils may be sampled and subject to analytical tests for particular compounds. This is relatively easy but expensive and beyond the scope of this study. A kind of backyard bio-assay was attempted, taking six samples of three different soils and sowing in each the seed of one E.camaldulensis or one E.diversifolia, so that each species was allowed to germinate and grow in each soil type. The three soil types were: untreated clay, simazine-treated clay and limey road rubble. The result was an indication of continuing suppression of weed emergence and of slowly developing stunting and yellowing of E.camaldulensis seedlings in the simazine-treated soil. Not much more than can be learned from looking at the pattern of weed growth on the ground, anyway. The yellowing and growth of the seedlings in the simazine-treated soil closely resembled those in the lime rubble consistent with the oft repeated observation that trees suffering lime-induced chlorosis and some in stages of Mundulla Yellows can be alike.

Before I leave the subject of bio-assay it should be noted that this can be a sensitive and cheap technique. Fourie (1992) used the barley plant to assay simazine in vineyard soils. Crude extracts may be prepared for trial on a test plant for the detection of an unspecified phytotoxic substance in the tissues of a sick plant. The backyard version above, was attempted because differential germination had been reported anecdotally (J. Cutten pers. comm.). This was not found here.

Leaf sample analysis of eucalypts is fraught with difficulty. Three samples of whole E.camaldulensis leaf from each of: a healthy tree, the worst side of a sick tree and the best side of that same tree growing in simazine-treated soil, were submitted. The intact simazine molecule was not detectable at 50 p.p.b. (State Chemistry Laboratory, Organic Chemistry Unit, work order 00-04-183). This level of detection is two orders of magnitude less sensitive than the routine testing of water samples where sub-p.p.b. levels are achievable (Blum et al. 1993). The time of sampling was in the order of 10 - 11 months since last herbicide treatment and as it turned out this season, about one month before re-treatment. The control tree was on my own property and the sick specimen was Polley's tree, mentioned below.

Tree distribution analysis yielded new empirical evidence. The preceding years of observation suggested that three useful measures might be taken. They are:

  • Breast height diameter (BHD) the standard and most natural measure of a tree's size, recorded in cm.
  • A distance in metres (DKZ) from the butt of the tree to the nearest total weed control kill zone.
  • Mundulla Yellows score (MYS) on a scale of 0 - 10 where 0 is healthy, 1 shows first stages of interveinal yellowing, up to 5 with half the crown frankly diseased and 7.5 when half the crown is dead, through to 10,, a dead tree. To score above 2, I must be convinced it is a case of Mundulla Yellows, below 2 may or may not be so.

Trees were scored at three sites; the Aqua Street drain and environs, the Boundary Road sugargums near the intersection of that road with Dawkins Road and the Booloman-minga property north of the Two Wells - Gawler Road. All sites are within the northern Gawler River floodplain.

Table 2. Sickness of trees associated with the Aqua Street drain
Those on the Polley property, above the dashed line, are responding to six annual herbicide doses. Those below the line, to a lesser number, over a shorter span. BHD is breast height diameter in cm, DKZ is distance from nearest total weed control kill zone in m, MYS is score of sickness on scale of 0 - 10 (See text.) Trees with more than one stem show a measure for each stem and the word multi describes a coppiced individual.
E.camaldulensis 30 3.5 5
E.camaldulensis 15 6 6
E.camaldulensis 20 6 3
E.cladocalyx 30 4 2
E.torquata 15 4 0
E.leucoxylon subsp. 10,10,10 4 0
E.leucoxylon subsp. 10,10 4 1
E.leucoxylon subsp. multi 4.5 0.5
E.leucoxylon subsp. 15 4.5 0
E.leucoxylon subsp. 15 5 0

E.camaldulensis 15 4 1
E.camaldulensis 20 4 2
E.camaldulensis 10,15 4 0.5
E.camaldulensis 15 3 1
E.porosa 10 4 0
E.porosa 10 4 0
E.porosa 10 4 0
E.porosa 10 4 0

In Table 2, I present the scores of trees along part of the Aqua Street drain. They fall into two groups, those on the Polley property (above the horizontal line) and those on Harman's. The first tree is the same Polley tree tested for simazine in leaf tissue. While DKZ measures are similar, size and species differences may be apparent. E.camaldulensis may be susceptible while E.torquata is tolerant (pers. obs. elsewhere). The section of drain in front of the Harman property may not have been poisoned as often as the Polley section (W.H. Harman pers. comm. and pers. obs.), accounting for the visibly lesser effect there. Not included in that table are some control samples, one of 18 trees all E.camaldulensis on my own property, all 65 metres from the same DKZ or 50 metres from another possible DKZ, had three scores of 0.5 and no suspicion of Mundulla Yellows. An additional control batch of 100+ trees of the same type could also be measured, they are all 40 - 50 m deeper onto the Polley property and show no signs of gross pathology of the type under discussion. DKZ 40+ score less than 2 (most 0) times 100.

Eucalyptus cladocalyx   
Fig. 5 Foliage of Eucalyptus cladocalyx (MYS = 9, DKZ < 1), note interveinal yellowing necrotic spotting and distortion.

The Boundary Road sugargums (Table 3) are all old trees and are adjacent to the same paddock, with the same land use and history, presumably. I had hoped that the trees along the unsealed Dawkins Road may have escaped the treatment applied to unsealed shoulders of sealed roads, but a sprayed culvert extends past four of them and only three old trees survive further down that road to give scores of 1 or 2 minus at a DKZ of 100+. The lowest DKZ and two very sick looking trees are associated with a treated E& WS indicator post or other fixture near their butts as well as the road shoulder. Just nearby is a healthy looking olive with a 3 m DKZ.

The Booloman-minga trees represented on Table 4 are one of the few remnant patches of native vegetation in our district, where observations may be made of the same species of tree both near a roadside and at some distance removed. The landowner, a lifelong local resident, assures me that no herbicide has been applied to the test block and presence of weed species supports this. The Gawler Road frontage of this block presents a different picture of sick and dying trees. There is however a multiple kill zone along this frontage possibly comprised of treated drain and road shoulder as well as a water meter and another E& WS fixture, and visible at the time of scoring. This despite the landowner's denial of any knowledge of such treatment and time elapsed since last treatment (reapplication occurred shortly after scoring and confirmed the drain maintenance practice at least). The result is a total weed control kill zone near the fence line of this property from which distances can easily be measured. A maximum DKZ of 16 m is demonstrated, beyond which trees are free of this disease. My hypothesis suggests that this is the reach of the-root system of mature E.porosa in this area. Within this zone trees may be healthy if they are smaller. Note the pair indicated on the table. They are quite close in the paddock but the 49 cm tree scores 9 while the 12 cm sapling scores 0.

Table 3. The Boundary Road sugargums, Eucalyptus cladocalyx
Those above the horizontal line were near a sealed road. Those below the line were near an unsealed road, the first four being near a culvert and drain showing clear signs of herbicide treatment. Only the last three trees were 100 m from obvious total weed control sites. Columns as in Table 2.
1 97 4 1
2 150 4 4
3 75 3 4
4 100 4 4
5 68 2 7.5
6 140 0 7
7 135 4 2+
8 100 4 3
9 75 4 7
10 75 4 8
11 90 4 6
12 80 3 7.5
13 80 3 7.5
14 100 3 2
15 80 3 8
16 75,75 3 7
17 80,50 2 7

18 75 1.5 7.5
19 75 1.5 6
20 75 1.5 5
21 75 2 6
22 100 100 1
23 100 100 1
24 100 100 2-
Table 4. The Booloman-minga, Eucalyptus porosa grove, in order of increasing DKZ
The asterisks denote a pair of trees close to one another, one mature and one a sapling. Columns as in Table 2.
1 26 0 7.5
2 20 0 7.5
3 35 0 1.5
4 24 0 3
5 25 0 7.5
6 20 0 10
7 29,30 0 5
8 20 0 7.5
9 14 0 3
10 multi 0.5 3
11 47 4 7.5
12 33,25 6 7
13 49* 7 9
14 65 10 2+
15 12* 10 0
16 100 13 0
17 64,41 13 0
18 13 16 0
19 73 16 3
20 37 16 5
21 43 17 0
22 16 18 0
23 56 19 0
24 40 28 0
25 30 38 2-
26 46 38 0
27 48 40 0
28 48,30 50 0
29 54 55 0
30 57 60 0
31 31 60 0
32 40 63 0


My course, from initial observation through concern and involvement, along the way to this presentation as it was given to the national conference, in the form of a personal historical narrative, and now turned into an expanded and annotated work suitable for publication, has been a long and winding road of discovery. Most of the obstacles encountered were intellectual ones of my own or some few were hurdles placed in my path by others. While, hopefully, never completely off the track, I did spend some time on matters seemingly unrelated to the practical problem of sick trees. Which were the most important parts of the track? Which lead most directly to the solution?

General directions need to be adopted early (McNamara 1991). One path I refused to go down was one which applies the notion that 'proof is necessary before action' to all circumstances. Surely the precautionary principle and risk management are the stuff of practical reality. What I have here is a strong and useful accordance, a consilience even, of different lines of evidence. Not the stuff of bureaucratic politics or academic rivalry, perhaps, but routine to such wise people as biostratigraphers, biogeochronologists and grandmothers.

Specific choices had to be made too. Was it necessary to prove:

  • that herbicides kill plants,
  • that trees are plants,
  • that trees have roots,
  • that atrazine and simazine are root adsorbed plant poisons, (no, the manufacturers tell us that),
  • that atrazine and simazine are translocated to the shoots, (no, the manufacturers give us that),
  • that roadsides have been treated throughout South Australia, (the relevant State minister tells me that is so), and similar practices have been confirmed for the State water utility, local government and pest plant control authority?
Eucalyptus camaldulensis   
Fig. 6 Branch of Eucalyptus camaldulensis with panic growth clipped for testing [same specimen as Figure 3].

Do I have to demonstrate just how much path and drive-way treatment is applied locally or can I simply suggest a look at the nearest garden supplies outlet? Here you may find, as I did in mid-May this year, some 100+ kilograms of 'brand - X' drive-way and path weeder, containing almost 50% simazine, in the basement of a city store. (Again that seasonal timing allows that kind of crucial observation to be made).

Important signs have to be recognised for what they are. This disease of trees and other plants is well enough defined for our purposes. The name is as good as any but may be unfair to the residents and landowners of Mundulla. The term 'Highways Department Yellows' may have been deserved but is too narrow in its focus. 'Utility Yellows' (McNamara 2000) is broader but seems to exclude private practice. 'Poisoning trees through their roots' may be the best descriptor but is cumbersome. One day we may have one word which means just this. Perhaps the verb, 'to mundulla', will be coined.

Having tracked down some confirmation of the routine use of plant poisons by some agencies I rested, content that observations had been confirmed and similar activities can readily be observed directly, at the right time of year. Mention has already been made of the 11 May 2000 spraying of a drain near my home. On 19 May 2000 this same ground was covered by a contractor working on behalf of the Adelaide Plains Animal and Plant Control Board, spot spraying weeds. Consequently, some patches of ground along this drain will have received twice a lethal dose of simazine and three times a lethal dose of glyphosate from the normal activities of just these two agencies. The technique observed was the training of a jet of fluid onto plants for a few seconds for total coverage to the point of run-off. Inspection showed extensive ground coverage to an extent that would indicate, volumes in the order of 0.5 to 1.0 litres of fluid per small plant, were used to produce the amount of flow and spread onto the soil. The Two Wells spokesman for this statutory authority assured me that glyphosate plus a pink dye was used in this area but in areas more remote from housing, a tank mix containing metsulfuron-methyl (one of the sulphonylureas) is employed.

The possibility exists for the dosing of tree roots in this way. Clearly in this example some patches of ground have received very large doses of glyphosate, a highly phytotoxic substance, capable of root absorption and translocation. If this technique is used with the addition of metsulfuron-methyl, say on weeds among remnant mallees, many more cases of Mundulla Yellows can be predicted, where the only sign might be some long-dead horehound or artichoke thistle. In fact Kraehenbuehl (pers. comm.) inspected a block of sick mallee and dryland teatree in the Avon area (northern Adelaide Plains) in which he found the whole ground under the trees "was pink". I have seen no evidence of the coordination of poisoning effort between agencies nor of effective notification to the public, who may have their own poisoning program. The use of marker dyes should be compulsory in all applications.

The mode of action of at least the older classes of herbicide are well known and standard texts carry sufficient information of these, especially in relation to crop plants and agricultural weed species. The effects on specific classes of native vegetation seem not to be readily available. I have found sufficient evidence only to indicate that symptoms exhibited by native taxa like Acacia and Eucalyptus are consistent with those derived from studies of other plants. A larger body of evidence may exist but I have been unable to gain access to it. Records of collateral or non-target poisoning produced by workers in the forestry of Pinus radiata over several decades and more recently in relation to Eucalyptus globulus, may be instructive if it can be brought to light. The evidence is, that both the triazine poisoning of acacias and eucalypts, and the named disease Mundulla Yellows, present the same face.

I have not inspected the site nor do I know what killed the redgums near Buckingham church at the original Mundulla locality. A long-term resident and a landowner, from this area, have denied any possibility of herbicide use or even the existence of weeds in the area. One gave a categorical denial of any possibility of herbicide use in the area (K. Walladge pers. comm., unpublished statement to SASA/AIH conference). This followed Knight's report of the presence of 2,4-D at 0.08 mg/kg in redgum leaf from Mundulla (State Chemistry Laboratory, Organic Chemistry Unit work number 00-05-225). Photographs of the eponymous locality, presented to the same conference, show almost total ground cover of Phalaris sp. a weed grass with some toxicity to stock, and high fire hazard. Anecdotal reports to me, indicate that attempts to control roadside Phalaris infestation were carried out in at least one part of the South East of South Australia in the early 1970s (T. Sim pers. comm.). Department of Agriculture or local pest plant control board archival material may elucidate the case. Heavy doses of 2,4-D in the past might explain the present vegetation - grasses being tolerant, but it is a notoriously volatile compound rightly suspected of long-range drift effects. Knight was right to infer nothing other than mere presence from this single test result. Nevertheless the reordering of vegetation through its tolerance/susceptibility response can indicate the chemical agent used to those familiar with their differing patterns of killing.

The olive is part of an emerging pattern of herbicide tolerance on drains and roadsides in the Two Wells area. I was aware of this when posing the question in relation to poison placement over the root system of the olive as illustrated in the diagram above. If the tree were E.camaldulensis and the poison atrazine at total weed control rates, one would expect chlorosis of part of the crown. If the plant were Olea or Schinus an appearance of rude vigour would be expected. There is wonderful variety in the metabolism of plants.

dscn2961.jpg (48K)   
Fig. 7 The prognosis. Two of three long dead Eucalyptus cladocalyx (MYS = 10, DKZ = 0), at an intersection. Note, staghead appearance with signs of panic growth. Note also, spontaneous regrowth of Schinus molle within the kill zone.

My leaf sampling for chemical analysis yielded no positive result. I should have heeded John Randles' suggestion, very early in my quest, that such testing of tree foliage was "impossible". Similarly the suggestion, reinforced by Peter Christy (of SA Water lab.), that activity may occur at levels below those of detection, and the suggestion of Bob Boardman of Forestry SA, that metabolism is rapid and quite effective in removing all trace of the original compound. Ironically the seasonal reapplication of simazine occurred early this year, just a few weeks after sampling - but with my new found respect for the metabolic capability of the redgum and lack of knowledge of the most likely metabolites, I decided to save my money.

The scoring of plants for BHD, DKZ and MYS is easy. One hour's work on the Booloman-minga block yielded useable data. The simplest explanation of the 16 m maximum DKZ (MDKZ) is indeed root reach. Most instructive would be a range of such measures for various taxa in the same area, so that short-rooted species may be compared with longer-rooted forms. I would expect sick Dianella to be closer to a given weed control zone than cohabiting mature eucalypts, for example. Indeed the ephemeral weeds at this locality, with their short lateral root systems, confirm this. They are confined to the kill zone, as dead plants and some species provide a halo of 0 - 0.5 m of sick plants beyond it. An alternative hypothesis of migration of the poison through the soil is not supported by the weed distribution, and the occurrence of healthy saplings within the MDKZ of their own species.

The Booloman-minga example is sufficient for my purposes, but this sort of empirical study bears repetition. With a little work an MDKZ may be measured for any given combination of variables. I urge workers with a more diverse native vegetation in their study sites to estimate these distances for a range of taxa to fill in the gap between the 16 m MDKZ of a eucalypt and the less than 0.5 m MDKZ of ephemeral weeds.

Paradoxically some quite healthy box gums do exist further along the Gawler road drain near my study area. Inspection reveals that their root systems have been severed by the drainage works, so their feeder roots would be, mostly some distance away from the drain itself. A useful observation for tree surgeons, perhaps, or tree owners with refractory neighbours.

Nothing of the scandalously little epidemiology published so far, by government funded agencies, suggests that an infectious biotic pathogen is implicated in the primary causation of this disease. Nor can it. Unless such microbial agents can be found to dwell within and be transmitted by the various fluids or equipment used by chemical spray contractors/operators, it will not be able to account for the distribution in space and in time of this particular epidemic.

Conversely the herbicide hypothesis offers the hope of immediate practical solutions, including stopping the use of root absorbed plant poisons. Any class of poisons adsorbed by the roots and translocated must be suspect.


What we have here is a community-wide problem. Key factors are:

  • the unwise use of plant poisons, especially those absorbed by the roots,
  • indigenous trees with very strong and efficient surface root systems,
  • soils that may be sandy, dry or alkaline or a combination of all those things.

May I suggest that this is a soil toxicity problem, possibly cumulative, and very likely primarily anthropogenic.

A causal relationship between root absorbed plant poison and these symptoms, developing and killing trees nearby can be mooted. To paraphrase White (1984), these observations reflect a causal pathway that runs from the environment of the plant to the disease.

The most radical thing claimed here is, that trees have roots, and we must be aware of them when applying plant poisons to the ground. Just as we should, if we allow the soil to be contaminated with any phytotoxic substance, within reach of the roots of any tree that we do not intend to kill.

Let us stop poisoning our trees, now.


I wish to thank my line-managers at the South Australian Museum, for sufficient academic freedom, and my colleagues Terry Sim and Terry Reardon. I wish also to thank M. Anthony, S.J. Appleyard, R. Boardman, R.F. Brown, J. Bourne, P. Bulman, P. Christy, G. Cotton, J. Cutten, G. Dalton, A. Day, H.J. Eckert, M. Elliott, J. Evans, M. Gemmell, E.L. Ghisalberti, B. Grigg, R. Inns, G. Jamieson, G. Kirby, K. Knight, E. Kokoschko, R. Kookana, D.N. Kraehenbuehl, D. Laidlaw, B. Larkin, S. Lenehan, S.C. McKillup, V. McLaren, D. Nicolle, B. Patterson, I. Polley, C. Preston, T. Reynolds, G. Roberts, R. Taylor, F. Ugody, W.J. Vaninetti, R.T. Wells, T.C.R. White, B. Williams, L.J. Williams, and R. Zammit. Thanks are also due to Graham C. Medlin for the computerisation of my original cut and paste type-script.


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* C.Dunlop, Chief Executive Officer, District Council of Mallala, in a letter to the author dated 15 December 2000, acknowledged that his council's policy had changed with resolution 2000/352 of 19 June 2000, which says "that triazine type herbicides such as simazine not be used by Council for weed control in or near drainage channels, rivers or areas where desirable trees and shrubs are within realistic root reach."

Manuscript completed, 30 August 2000.
e-mail: mcnamara.jim@saugov.sa.gov.au


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Australian Plants online - September 2002
Association of Societies for Growing Australian Plants