Chemical Control of Blue Periwinkle (Vinca Major

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Plant Protection Quarterly Vol.14(2) 1999 47 management due to the threat which the Chemical control of blue periwinkle (Vinca major L.) weed poses to nature conservation values, the localized nature of both infestations in Croajingolong National Park, Victoria and the high potential for eradication from the Park (Twyford and Humphrey K.L. TwyfordA,C and G.S. BaxterB 1993). A Department of Natural Resources and Environment, Gippsland Region, Despite the significance of blue periwinkle as a major threat to native vegeta- Orbost, Victoria 3888, Australia. B tion in southern Australia, documented School of Natural and Rural Systems Management, The University of accounts of control measures are limited. Queensland, Gatton College, Queensland 4345, Australia. SA NPWS (1989) recommend spot spray- C Present address: National Parks and Wildlife South Australia, PO Box 39, ing of actively growing plants with tri- Kingscote, South Australia 5223, Australia. clopyr in water. Control using glyphosate is recommended in Tasmania (Harris 1991, Robin 1991). Recommendations for Abstract mechanical control of small infestations Blue periwinkle (Vinca major) is a seri- blue periwinkle as one of the top eight are also available (Anon. 1991, Robin ous environmental weed of protected ar- weeds of concern to public land managers 1991). eas in eastern Australia. A trial to evalu- (Williamson 1991). This trial evaluated four herbicides to ate the effectiveness of glyphosate, In East Gippsland, major infestations of determine which was the most effective metsulfuron methyl, clopyralid and tri- blue periwinkle occur along the lower herbicide in the management of this seri- clopyr for controlling this weed was un- Snowy River (Edwards and May 1990) ous environmental weed. dertaken east of Mallacoota Inlet within and Tambo River. These infestations rep- Croajingolong National Park, Victoria. resent a serious threat to the conservation Study area The herbicides had their greatest effect values of remnant riparian vegetation and The trial site was situated in a coastal lo- six months after treatment. Brown-out at downstream protected areas. Populations cality within Croajingolong National that time was 96% with glyphosate at 360 of blue periwinkle in Croajingolong Na- Park, east of Mallacoota Inlet, Victoria g 100 L-1, 59% with triclopyr at 126 g 100 tional Park in far eastern Victoria are lim- (149° 45'E, 37° 31'S) (Figure 1) on a gentle, L-1, 23% with clopyralid at 150 g 100 L-1 ited to relatively small infestations at southerly-facing slope bounded by par- and negligible with metsulfuron methyl Gipsy Point and Bakers Bight. At these lo- tially cleared private property to the north at 6 g 100 L-1. cations the species is a high priority for and low-lying swamp vegetation to the

Introduction Blue periwinkle (Vinca major L.) is a vigorous perennial prostrate creeper originat- ing from the Mediterranean (Swarbrick New South Wales and Skarratt 1994). It is a serious environmental weed in temperate regions of southern Australia and New Zealand. This plant is naturalized in State Forest and conservation reserves in Western Australia (Keighery 1991), South Aus- tralia (SA NPWS 1989), the Sydney region (Smith and Patterson 1978, Smith 1983), Tasmania (Young 1992), the ACT and Lord Howe Island (cited in Swarbrick and Skarratt 1994). It is considered to be a significant problem weed of protected areas Victoria (Williams and Timmins 1990) and urban environments (Elser 1988a) in parts of New Zealand. It frequently occurs in very Trial site large infestations in the semi-shade of trees. Seed set is low in New Zealand (Elser 1988a) with most spread being a vegetative marginal advance of the infes- tation. The procumbent stems of up to one Mallacoota metre long, can root at the tips (Elser 1988b) and nodes (SA NPWS 1989). The dumping of garden refuse is an important means of spread (Elser 1988c, Anon. 1991). Blue-purple flowers are produced prima- Croajingalong National Park rily in spring. In Victoria, blue periwinkle has been recorded invading seven of the 15 vegetation formations recognized by Carr et al. (1992) who classified it as a very serious kilometres threat to native vegetation. An interim survey of the most important environmental weeds within Victoria identified Figure 1. Location of trial site. 48 Plant Protection Quarterly Vol.14(2) 1999 south. The extent of blue periwinkle in the was added to metsulfuron methyl at the stems and roots within the glyphosate area is generally limited by these physical rate of 1:140. Adjuvants were not included treated plots. Regeneration from seed was features. Deep black tertiary sands with with any of the other herbicides. Prostrate evident in the form of a small number of high organic matter underlie the site. Ex- stems between plots were severed prior to seedlings. act soil depth was not determined but spraying to eliminate the potential for The average rank of brown-out pro- steel pegs penetrated to a depth of about translocation of herbicides into adjoining duced by triclopyr, clopyralid and met- 30 cm without hitting rock. plots. sulfuron methyl were not significantly Vegetation comprised tall coastal scrub Percentage cover of blue periwinkle different at 6 MAT (for pairwise compari- dominated by black wattle (Acacia was visually assessed in each plot prior to sons respectively z = 0.49 and 1.85, P = 0.15 mearnsii, 10–15 m high) with giant honey- herbicide application (Table 1) and at 1, 2, and 0.06). Physiological effects of triclopyr myrtle (Melaleuca armillaris, 3–5 m high) in 4, 6, 12 and 18 months after treatment (126 g 100 L-1) were clearly apparent at 1 the mid-storey. Jasmin morinda (Morinda (MAT). Herbicide effects were recorded as MAT with the majority of blue periwinkle jasminoides) and wombat berry (Eustrephus percentage brown-out for blue periwinkle plants being severely wilted. Tissue yel- latifolius) occur as climbers in both tree and noted for non-target species at 1, 2, 4, lowing was evident at this stage and be- species. Scattered individuals of cherry 6, 12 and 18 MAT. Recolonization by na- came more prevalent at later assessments ballart (Exocarpus cuppressiformis, 3–5 m tive and exotic species was recorded. leading to a moderate level of brown-out high) are also present. Shrubs are an un- The data were heteroscedastic and not at 2 and 4 MAT of 18% and 30% respec- common component of the vegetation due amenable to transformation, thus we tively. By 6 MAT most blue periwinkle to the vigorous growth of blue periwinkle. could not use parametric analysis, such as plants were herbicide affected and leaf Shrub species present include scattered ANOVA, which would have allowed brown-out had reached a mean of 59%, the giant honey-myrtle and, where more comparison of effectiveness over time. The highest for the trial duration. However, open, shiny cassinia (Cassinia longifolia). non-parametric Kruskall-Wallis test was treatment results using triclopyr were par- Isolated individuals of mock-olive used for all herbicides at 6 MAT, when all ticularly inconsistent at 6 MAT with (Notolaea venosa) and blackberry (Rubus treatments had greatest brown-out. The brown-out levels ranging from 5 to 90%. fruiticosus agg.) were also present. null hypothesis was that the observations Monitoring at 12 and 18 MAT indicated The ground flora was almost com- of brown-out for each herbicide were that blue periwinkle was recovering from pletely dominated by blue periwinkle par- taken from populations which had the herbicide effects (mean brown-out of 44% ticularly on the mid-slope. In some places, same statistics of location (Sokal and Rohlf and 36% respectively) through reshooting particularly closest to private property, 1981), i.e. that the degree of brown-out combined with some regeneration from introduced pasture grasses were present was the same for each herbicide. Follow- seed. as co-dominants. The most common asso- ing a significant result the mean ranks of Clopyralid (150 g 100 L-1) failed to show ciated species included arum lily brown-out for each herbicide were com- any large effect upon blue periwinkle un- (Zantedeschia aethiopica), austral bracken pared using the z statistic (Piggott 1986). til 6 MAT when maximum brown-out (Pteridium esculentum) and spiny-headed (23%) was reached. Similar to triclopyr mat-rush (Lomandra longifolia). Results treatments, plots where clopyralid was Effects of chemical treatments on blue applied responded inconsistently with Methods periwinkle brown-out at 6 MAT ranging between 5 Four treatments and a control were ar- All treatments reached their greatest and 60%. By 12 MAT, all plots showed ranged in randomized blocks with three brown-out at 6 MAT (Figure 2). At that significant recovery including reshooting (clopyralid, control) and four (glyphosate, time glyphosate (360 g 100 L-1) was more from previously damaged stems. At 18 metsulfuron methyl, triclopyr) replica- effective than any other treatment (H ad- MAT, brown-out was still evident in one tions of 4 × 4 m plots (Table 1). All herbi- justed for ties = 15.21, P = 0.004: z = 2.8, P = plot although the strong vegetative recov- cides were mixed in clean fresh tap water. 0.005). Leaf yellowing and initial brown- ery observed at 12 MAT had continued. As none of the chemicals used have label out were evident at 1 and 2 MAT (mean The only effect observed from mesul- recommendations for control of blue peri- brown-out of 11 and 45% respectively) furon methyl (6 g 100 L-1) throughout the winkle, herbicide concentrations were se- and tended towards substantial (79% at trial was an extremely small amount of lected based on experience with control of 4 MAT) and then almost complete brown- yellowing and an even smaller amount of weeds of a similar climbing vine habit out (96%) at 6 MAT. Extensive brown-out brown-out (<1% to 3%) observed across elsewhere in the region. at 12 and 18 MAT were still apparent (83 the assessment period. This small amount All treatments were applied on 25 Feb- and 70% respectively) although the over- of brown-out was not significantly more ruary 1992 when the temperature was all cover of live blue periwinkle had be- than found in the control plots (z = 2.24, 22°C, relative humidity 40%, no cloud gun to increase due to invasion of plants P = 0.04). cover and there was a light south-easterly from adjacent plots and untreated areas. wind of 0–5 knots. Herbicides were foliar The general effectiveness afforded from Effects on non-target species applied using a 15 L knapsack at a volume glyphosate application was evident from Glyphosate resulted in mortality of most of 3.5 L per plot (or 2188 L ha-1). Surfactant the extremely low rate of regrowth from ground and understorey species sprayed.

Table 1. Herbicides and rates evaluated, blue periwinkle cover pre-treatment and treatment replication. Herbicide Trade name Concentration Rate Mean blue periwinkle No. of (g 100 L-1) (kg ha-1) cover prior to replicates treatment (%) (4 × 4 m plots) Metsulfuron methyl Brushoff®, Dupont Australia (see note) 6 0.13 80 4 Glyphosate Roundup®, Monsanto Australia 360 7.88 88 4 Triclopyr Garlon 600®, DowElanco 126 2.76 75 4 Clopyralid Lontrel®, DowElanco 150 3.28 77 3 Control (no herbicide) – – – 80 3 Note. Nufarm surfactant was added to metsulfuron methyl at the rate of 1:140. Plant Protection Quarterly Vol.14(2) 1999 49 between trial plots. Clopyralid (15 g 100 Metsulfuron methyl L-1) and metsulfuron methyl (6 g 100 L-1) 100 Glyphosate were ineffective. Triclopyr Although glyphosate application re- Clopyralid sulted in initial high mortality of native No herbicide understorey species, this outcome was of 80 little long-term consequence as regeneration of native species from seed was strong once the dense and vigorous cover of blue periwinkle was reduced. Follow 60 up spot spraying of weed regrowth at between 6 and 12 MAT as recommended from these trials should be directed to avoid native understorey species and be 40 undertaken when blue periwinkle is most actively growing. Percentage brown-out The success of glyphosate in opera- tional control programs for blue periwin- 20 kle has been subsequently demonstrated at an area adjoining the Bakers Bight trial site where a mortality rate of greater than 95% was achieved. Interestingly, high 0 populations of the exotic garden species, 1 2 4 6 12 18 snowflakes and daffodils (Narcissus sp. L.), have appeared after blue periwinkle Months after treatment (MAT) control indicating the importance and ne- cessity for follow-up control of secondary Figure 2. Percentage brown-out of blue periwinkle 1–18 months after weed species which emerge after the sub- treatment (MAT). Mean + 95 % confidence interval. stantial removal of the primary weed in- festation. Throughout the trial an overall increase in The death of a giant honey-myrtle shrub Indications from this trial were that the cover of native species was observed may have been attributable to root uptake arum lily, another serious environmental in glyphosate plots with the reduction in of herbicide as no other apparent cause for weed in temperate Australia (Keighery the vigorous growth and cover of blue mortality was evident. At 6 and 18 MAT, 1991, Carr et al. 1992), may increase and periwinkle. Native ground flora such as snowflakes (Leucojum aestivum L.) were expand it’s range once the competition New Zealand spinach (Tetragonia tetra- recorded (cover <5%) in one plot for the from blue periwinkle was reduced. Given gonioides) increased in cover between pre- first time. the highly invasive nature of arum lily, and post-control assessments through nat- control of this species warrants a high pri- ural seed regeneration. There was less re- Discussion ority. Observations from this trial and generation of giant honey-myrtle through Glyphosate applied at the rate of 360 g 100 elsewhere (e.g. Parsons and Cuthbertson seed than of New Zealand spinach. L-1 during February provided the most 1992) have indicated the effectiveness of Triclopyr caused mortality of all non- effective control of blue periwinkle in sulphonyl urea compounds such as chlor- target broad-leaved ground flora with the this trial. Maximum foliage death was sulfuron in controlling this species. exception of arum lily which displayed achieved at 6 MAT. Although further tri- leaf yellowing at 1 and 2 MAT but recov- als are required to ascertain the most ef- Acknowledgments ered from any herbicide effect from 4 fective time for re-application of gly- The following Department of Natural Re- MAT and thereafter. The death of one gi- phosate, the results of this trial suggest sources and Environment staff based at ant honey-myrtle shrub (over 1.5 m high that follow-up spot spraying of stem and Mallacoota and Cann River assisted with and not foliarly sprayed) may have been root regrowth and seedling regeneration establishing and monitoring the trials: caused by herbicide uptake through basal would be best undertaken between 6 and Phil Reichelt, Peter Humphrey, Rod Collo- bark tissue. 12 MAT. cott, Rod Newnham, Tim Everington, Clopyralid had very little if any effect An important prerequisite for maxim- Maurice Hawkins and David Harper. on non-target ground flora and no effect izing the impact of glyphosate is deliver- John Whitehead and Kathryn Bullen and on understorey shrubs. Leaf yellowing in ing it at a time when the target weed is ac- two anonymous reviewers made helpful individual specimens of arum lily was evi- tively growing and photosynthesizing (J. comments on a draft of this manuscript. dent, but brown-out and mortality of this Whitehead personal communication). species was not recorded. Arum lily in- Targeting glyphosate application to peri- References vaded one plot in the absence of any ap- ods when maximum sap flow to the roots Anon. (1991). Common garden plants that preciable reduction in blue periwinkle is occurring is important for control of per- are environmental weeds in the Upper and increased in cover from 5% prior to ennial plants. Given the high mortality Yarra Valley and Dandenong Ranges treatment to 35% at 18 MAT. rate of blue periwinkle observed in this area. Educational kit prepared by the Metsulfuron methyl had a selective ef- trial through application of glyphosate in Regional Pest Plant Strategy Working fect on non-target ground flora. Arum lily February, it is recommended that future Group, Belgrave, Victoria, p. 1. suffered wilting at 2 MAT and brown-out control programs targeting this species be Carr, G.W., Yugovic, J.V. and Robinson, by 6 MAT in some plots due to the appli- undertaken when seasonal conditions are K.E. (1992). ‘Environmental weed inva- cation of herbicide, as did austral bracken contributing to the production of vigorous sions in Victoria’, p. 56. (Department of and giant honey-myrtle. Other ground plant growth. Conservation and Environment, and flora such as grasses were not affected. Application of triclopyr (126 g 100 L-1) Ecological Horticulture Pty. 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