Neither metalaxyl (100 mL of a solution of 2.0 g a.i./L, applied as a root drench to 10-L pots) nor phosphonate (foliar spray at 1.0 g a.i./L, applied to runoff) controlled Phytophthora cinnamomi stem infection of Leucadendron laureolum x L. salignum hybrid when applied 10 days after inoculation. Both fungicides were most effective when applied prior to inoculation.Neither fungicide was able to kill P. cinnamomi within established infections. The fungus survived within the vascular tissues of treated plants. Infection was confined to cortical tissue by wound periderm when the rate of tissue invasion by P. cinnamomi was slowed by the fungicides.The results confirm observations made in protea growers' fields that with highly susceptible species, systemic fungicides can have poor curative properties and should be used as a prophylactic, in conjunction with other disease control methods.

When propazine was used continuously for 5 years as a pre-emergent herbicide in a large Pinus radiata nursery at Benalla, where the soils were not believed to be conductive to Phytophthora cinnamomi root rot, disease appeared after ca 2 years and rapidly increased in intensity despite attempts to control it with fungicides. The disease and the fungus virtually disappeared, within one season, when chlorthal dimethyl replaced propazine.An explanation for these observations was sought by examining the effects of propazine and chlorthal dimethyl on soil, rhizosphere and rhizoplane bacteria, Actinomycetes and fungi and the effect of the herbicides on the resistance per se, of P. radiata seedlings to Ph. cinnamomi. These tests were carried out in a laboratory, phytotron and greenhouse.The nursery disease symptoms were reproduced in the phytotron when Ph. cinnamomi-free soils were inoculated and treated with both herbicides. Chlorthal dimethyl was found to strongly inhibit root disease and soil inoculum potentials of Ph. cinnamomi in 5 month-old seedlings while propazine had the opposite effect. When the stems of herbicidal-treated seedlings growing in Ph. cinnamomi-free soils were inoculated with Ph. cinnamomi, there was evidence that propazine increased disease sensitivity considerably while the effect of chlorthal dimethyl was not consistent.Examination of the effects that both herbicides had, in phytotron tests, on soil, rhizosphere and rhizoplane microflora showed that chlorthal dimethyl reduced numbers of Gram-positive and -negative and spore forming bacteria ca 90% while propazine increased their numbers. In the rhizosphere and rhizoplane the inhibitory effect of chlorthal dimethyl and the stimulatory influence of propazine on bacteria was very variable which suggests that the root exudates had a greater influence on microbial numbers than that of the herbicides.Examination of the effects various bacterial types on sporangial formation of Ph. cinnamomi showed that the spore-forming bacteria associated with propazine soil drenches strongly stimulated sporangial production.The evidence suggest that the disease outbreak at the Benalla nursery may have been due to an increase in numbers of soil bacteria that stimulated production of Ph. cinnamomi inoculum and a reduction in disease resistance. The disease reduction following applications of chlorthal dimethyl may have been due directly to fungitoxicity to Ph. cinnamomi and failure to stimulate soil microflora that may have increased inoculum levels. Its influence on disease resistance of P. radiata was possibly negligible.

Some of the morphogenic and histological features of mycorrhizal symbiosis relevant to the possible evolution of mycorrhizas are reviewed. In doing so, a number of assumptions are made regarding beneficial and inimical factors guiding the process of evolution. These are associated with escaping from microbial antagonism (in its widest sense) in the soil, overcoming the defensive reactions of the host, obtaining a steady supply of nutrients, and improving the efficiency of the host's roots.On the basis of these assumptions, it appears that mycorrhizas could have developed as soil microbes started to colonise rhizospheres and rhizoplanes. Some of the rhizoplane microbes developed a parastic life style, eventually giving rise to minor pathogens of root, root necrotrophs and a very small and highly specialised group of root biotrophs. Excepting vesicular-arbuscular mycorrhizas - early, widespread and widely distributed types of mycorrhizas bearing little relationship to other forms - ectomycorrhizas seem to be of the earliest type from which others developed as intercellular invasion gave way to intracellular infection, and as mantles and Hartig nets were reduced. On this basis, the ericoid and orchid mycorrhizas could be regarded as the most advanced.

In an investigation into the side effects of herbicides on mycorrhizal formation in Pinus radiata nurseries, propazine and chlorthal dimethyl were added at concentrations that approximated to normal (2.20 and 1.88 g a.I-1L) and half-normal (1.10 and 0.94 g a.i.-1L) field application rates respectively to P. Radiata seedlings growing in terra cotta pots. A humus-rich, surface soil from a 40-year-old P. radiata plantation was used as mycorrhizal inoculum. Root length, mycorrhizal numbers and type, and seedling growth were assessed and a histological examination of bulk mycorrhizal samples was carried out. Propazine applied at both dosage rates and chlorthal dimethyl at the higher rate significantly sup- pressed root growth during the first 3 months and mycorrhizal formation during both the early and later stages of growth. However, neither herbicide affected shoot growth after 3 months and both increased shoot growth at the end of 6 months. Two mycorrhizal types were identified, a white-coloured, heavily dichotomised ectomycorrhiza with a thick mantle and a reddish-coloured, weakly dichotomous ectendomycorrhiza. The roots of chlorthal dimethyl treated seedlings strongly suppressed intracellular penetration in the ectendomycorrhiza, producing an unusual association with only a Hartig net, which was similar to that seen in senescing associations and some long roots of conifers. The ratio of white to red mycorrhizal numbers was highest in the untreated controls and was reduced by both herbicides. Both herbicides appeared to effect mycorrhizal formation through their influence on root morpho- genesis and host physiology.

The efficacy of dimethomorph, (E,Z)-4-[3- (4-chloropheny1)-3-(3,4-dimethoxypheny1)-1 -acryloyl] morpholine, in controlling Phytoplzthora cinnanionii stem infections of Rhododendron, Leucadendron and Eucalyptus was compared with that of fosetyl-Al, metalaxyl and phosphonate (potassium dihydrogen phosphonate) in a phytotron and greenhouse. The plants were inoculated on the stem and the effect of the fungicides applied either as foliar sprays or root drenches on lesion development was measured. The results showed that dimethomorph inhibited lesion extension when applied as a soil drench at rates of 0.6 and 1.2 mg a.i./mL. When used as a soil drench dimethomorph was about as effective as fosetyl-A1 and somewhat less effective than metalaxyl. When applied as foliar sprays, dimethomorph was ineffective and phosphonate was markedly superior to fosetyl-Al. Single applications of the fungicides tested were not able to kill P. cinnanzonzi in established infections within the duration of the experiment and under the test conditions which strongly favoured the fungus. Dimethomorph was slightly phytotoxic to Eucalyptus sieberi at dosages of 1.2 mg a.i./mL.

The rate at which root collar infection, caused by Phytophthora cinnamomi Rands, developed in Eucalyptus sieberi L. Johnson was tested by growing 40, 6-month-old seedlings in cores of disease- suppressive (DSS) krasnozem-type soil that had either been treated or not treated with steam. The core soil was inoculated by repotting the seedlings in a jacket of steamed or unsteamed sand or krasnozem that had been mixed with a mycelium-chlamydospore suspension. Disease development was of the compound interest type (sens. Van der Plank) and was slower in unsteamed DSS core soils. Inoculum density (ID) increased more than 10 times at the end of all tests, and the time taken for collar infection to appear was shortened when the inoculum was mixed with unsteamed DSS. The fungus was isolated more frequently from the collar of seedlings growing in steam-treated than in unsteamed DSS. The results showed that the soil used was only mildly disease-suppressive and suggest that post- infection antagonism may be the cause of slower disease development rates in DSS. Introduction

When Eucalyptus sieberi was grown in either a steamed or unsteamed krasnozem that suppressed Phytophthora cinnamomi root rot and repotted when either 6 or 12 weeks old in a larger container of inoculated sandy loam, seedling survival was significantly greater in the unsteamed treatments. By varying the treatments in the inner core soil and outer inoculum jacket, substituting a biologically inert coarse sand in place of the krasnozem in the core, and using eucalypt species of varying disease tolerance while maintaining very strict hygiene conditions throughout these experiments, it was possible to either demonstrate or deduce that: (a) the seedlings were killed when infection spread into the major roots, root collar and lower stem; (b) the microflora in the unsteamed krasnozem appeared to slow down the decay process within the root, possibly when the fungus was attempting to establish itself within the root; (c) the phenotypic resistance of a seedling to root disease depended, inter alia, on its genetic resistance and on the microflora in the surrounding soil; (d) once the fungus was established in the suberized tissues the microflora in the external environment had no influence on disease.

Summary It is proposed that “bird's eye”, a common timber defect of Eucalyptus regnans, be renamed “moth pocket” because of its origin and appearance. The defect is formed by an unidentified Lepidoptera larva feeding on the cambium and/or wound tissue over a 3–7 year period. Ultimately a roughly conical cavity filled with faecal pellets and sometimes kino is created. The cavity is formed by localised suspension of wood formation by the larva feeding at the inner bark (phloem) surface. Kino vein formation is usually suppressed until after the insect has emerged through a tunnel traversing radially through the bark. Although the damage done by the defect is negligible, the associated kino veins could impair wood quality.

For many years large patches of stunted and chlorotic seedlings, of which many died (Figures 1 and 2), have been seen in the rad iata pine (Pinus radiata D. Don) nurseries at Rennick, Victoria, near the South Australian border. The damage could not be traced to soil nutritional deficiencies, or root pathogens like Phytophthora cinnamomi Rands or Sclerotium batatico/a Taub. The soils were usually infected with Pythium and Fusarium spp. (Kassaby pers. comm.) but the ep idemiology of this disease did not fit the accepted pattern of the disease these fungi produce on radiata pine. The present nursery is seven years old and the disease was first recorded in 1978. It has worsened progressively. The soils are sandy, structureless, well drained and very low in organic matter. Consequently the pines are rotated with the following crops: first year, peas (Pisum sativum), Japanese millet (Echinoch/oa trumentacea) and lupin (Lup inus angustifolius); 2nd year, Japanese millet and oats (Avena sativa); followed by pine in the 3rd year. Each rotat ion was fertilized. The fertilizers applied to the pine crop alone are : presowlng, blood and bone (5% N, 5% P) at the rate of 400 kg/ha 4 weeks prior to sowing , "P ivot 200" (12% N. 8% P, 16% K, 11% S) at the rate of 200 kg/ha and MgS04 (100 kg/hal. Post-sowing foliar fertil izers were added every 3 weeks (10 applications/season) at the rate of MgS04 40 kg /ha, "Aquasol" 10 kg/ha, "N itrophoska Blue Special" (12% N. 5.2% P, 14.0% K, 0.5% B, 0.1% Zn, 7.0% S, 5.6% Ca, 1.2% Mg) at the rate of 10 l/ha: and prior to lifting , ZnS04 7H20 was added at the rate of 3.3 kq/ha, The rotational sequence had not always been followed and in late 1982 and early 1983 large disease patches appeared among the seedl ings in the bays where radlata pine had been successively cropped. Less disease appeared in the other bays where the prescribed crop rotat ion occurred. In it ial exam ination of "healthy" and " di seased" seedlings at Rennick showed (Table 1) highly significant weight and height differences. The lateral roots of d iseased seedlings were dark, brownish-black in colour

Ferns from a number of nurseries were found over the last three years to be affected by a foliar disease associated with the nematode Aphelenchoides fragariae (Ritzema Bas) Christie. (Table 1). The disease was detected mostly in samples sent for diagnosis by nurserymen late in autumn and in winter when symptoms were most distinct. The symptoms in A. aethiopicum, B. cartilagineum, P. aureum, P. tremula and P. quadriaurita were identical to those ascribed to A. fragariae (1), i.e. the leaves had either yellow, brown or black necrotic blotches that were sharply delimited by leaf veins. In ferns with parallel venation the blotches were banded and where the

Brasier (3), in searching for information on the distribution of Trichoderma species on roots, cited a study of the relative frequency of each species to the total Trichodermma population of Pinus roots (6). For comparison, these results were included in Table 2 along with equivalent data collected in the present study from eucalypt roots. Whereas 90% of the Trichoderma isolates from Pinus roots were species likely to elicit the 'Trichoderma effect' , only 12% of those from eucalypt roots were likely to be stimulatory. Although comparative information is not available for the pine, some 3200 washed and plated segments (2 mm long) of eucalypt root yielded only seven isolates of species known to cause the 'Trichoderma effect' in vitro. In the study some 3400 fungal isolates were collected from 130 plants over a 330-day period. The source of the Trichoderma isolates is shown in Table 3. This study was restricted to certain fungi isolated from the roots of only two eucalypt species. Furthermore, the eucalypts were grown under greenhouse, not field, conditions and the ability of root isolates to elicit the 'Trichoderma effect' was assayed in vitro. Within the limits of this study, it would appear that the roots of both a P. cinnamomi resistant eucalypt and a P. clnnemomisusceptible eucalypt harbour few fungi known to stimulate oospore production in P. ctnnemomt.

A krasnozem from the foothills of Mt Dandenong, Victoria, was found to strongly suppress root disease of Eucalyptus sieberi and E. obliqua seedlings caused by Phytophthora cinnamomi. Soil factors associated with disease suppression were examined in a phytotron by altering soil structure, using a hammer mill, sieves of various sizes and changing the soil microflora with steam at 60 and 100°C. E. sieberi, E. obliqua and E. globoidea were used as test seedlings. The results showed that the suppressive activity depended on the soil microflora and their association with the aggregates in the krasnozem. P. cinnamomi was found to kill seedlings by girdling the base of the stem and/or major roots. Some evidence showed that in unsteamed krasnozem aggregates many small roots were infected but few large roots and no stems were girdled, suggesting that post-infection antagonism occurred within the root. Field isolations from dead and dying E. sieberi, E. obliqua and E. regnans showed that P. cinnamomi infected the stems and major roots.