26 Plant Protection Quarterly Vol.18(1) 2003 three treatments) with five replicates of each treatment. In August 2000, before Sparaxis bulbifera (Iridaceae) invading a clay based treatment, the number of S. bulbifera adults wetland on the Swan Coastal Plain – control methods (flowering plants) and juveniles (non flow- ering plants) in each plot was counted and and observations on the reproductive biology a cover estimate (Braun-Blanquet) scored for each species (native and introduced) in Kate Brown and Kris Brooks, Environmental Weeds Action Network, each plot. In early October 2000 the her- c/- Swan Catchment Centre, PO Box 1906, Midland, Western Australia 6936, bicide was carefully spot sprayed in each Australia. Email: [email protected] treatment. As this weed grows very closely amongst the native herbs and shrubs these were also subject to herbicide application. Metsulfuron methyl (Brushoff®, 600 g kg-1 metsulfuron methyl) was applied from a Summary competition from weeds such as Sparaxis 15 litre backpack sprayer at 2.5 g ha-1 and Sparaxis bulbifera, a cormous geophyte bulbifera. This South African cormous spe- at 1.0 g ha-1 and chlorsulfuron (Glean®, 750 from the Cape Region of South Africa, cies is a serious invader of clay based wet- g kg-1 chlorsulfuron) was applied at 2.5 g is a serious invasive weed of clay based lands on the Swan Coastal Plain (Hussey ha-1. All were applied with the penetrant wetlands on the Swan Coastal Plain. et al. 1997). Once established it forms dense Pulse® (1000 g L-1 polydimethylsiloxane) Where it invades these wetlands it forms monocultures displacing herbaceous flora at 2 mL L-1. The plots were rescored in dense monocultures, displacing much of in particular. Given that around 50% of the September 2001. Differences in counts be- the rich native herbaceous flora. Herbi- native flora at Brixton Street comprises an- tween treatments and years were analysed cide trials were conducted in the Brixton nual or perennial herbs, many of them rare using Kruskal Wallace ANOVA with post Street Wetlands south east of Perth, or restricted taxa (Keighery and Keighery hoc Mann-Whitney U-tests used to de- where it is invading shrublands and 1995), S. bulbifera poses a significant threat termine significance between individual herblands, and impacts of treatments to conservation values of the wetland. treatments. Plant nomenclature gener- on co-occurring native species recorded. Options for control of a weed growing ally follows Paczkowska and Chapman Metsulfuron methyl was trialed at 1.0 g closely among native plants in a wetland (2000). ha-1 and at 2.5 g ha-1 and chlorsulfuron situation are limited. At Brixton Street any Plants of S. bulbifera were also moni- at 2.5 g ha-1. All treatments significantly control program needs to take place over tored over time to determine bulbil and reduced the number of juvenile and a short time at the beginning of October as seed production and methods of spread. adult plants of S. bulbifera. Metsulfuron the wetland begins to dry out and before methyl at 2.5 g ha-1 was the most effective S. bulbifera comes into full flower. Hand Results reducing the number of adult plants per removal at this time is one option and is Sparaxis bulbifera control plot from a mean of 25.4 to 0.4 and the a particularly useful tool for removing All herbicide treatments significantly number of juvenile plants from a mean small isolated populations growing in reduced the number of both adult and ju- of 373.2 to 28.8. relatively undisturbed bushland. How- venile S. bulbifera plants in the trial plots. There were 27 species of native taxa ever hand removal is labour intensive and Metsulfuron methyl at 2.5 g ha-1 was the scattered across the trial plots and only consequently needs to be integrated with most effective followed by chlorsulfuron two taxa, Sowerbaea laxiflora and Phily- a carefully targeted chemical control pro- at 2.5 g ha-1 then metsulfuron methyl at drella drummondii appeared to have been gram. Trials in recent years have indicated 1.0 g ha-1. Metsulfuron methyl at 2.5 g adversely affected by the herbicide treat- that the sulfonylurea group of herbicides ha-1 was significantly more effective than ments. The results however were com- can be quite effective against a number of metsulfuron methyl at 1.0 g ha-1 in control- pounded by the spatial distribution and introduced bulbous and cormous species ling adult plants (Figure 1). Apart from the seasonal nature of the native flora. (Pritchard 1991, Dixon 1996, Pritchard this there were no significant differences Additional information on the reproduc- 1996, Peirce 1998, Meney 1999, Brown et between treatments. Although all treat- tive biology and spread of the weed was al. 2002). Observations and data indicate ments significantly reduced the number of also recorded. that some introduced bulbous or cormous juvenile plants, a mean of 28.8 (±15.08) in- species invading bushland can be control- dividuals per plot still remained following Introduction led with sulfonylurea herbicides with the most effective treatment (Figure 2). The Brixton Street Wetlands lie 20 km minimal impact on the native flora (Dixon south east of Perth at the foot of the 1996, Meney 1999, Moore 1999). Brown et Herbicide impacts on native plants Darling Scarp. A small 19 ha remnant al. (2002) in detailed studies on the con- There were 27 species of native plants on the winter wet flats of Guilford trol of Lachenalia reflexa with metsulfuron recorded from across the trial site; five formation clays, the wetlands have an methyl at 5 g ha-1 in a Banksia woodland shrubs, 14 perennial herbs (seven of those exceedingly diverse flora of 307 native found indications of minimum impact on geophytes) and eight annual herbs. Not taxa (Keighery and Keighery 1995). Spe- co-occurring native species. all species occurred in all plots. Of the five cies rich herblands cover the winter-wet With little published information shrubs, three species remained unchanged claypans, herb rich shrublands the clay on herbicide control of S. bulbifera this or increased in cover across all the herbi- flats and Eucalyptus calophylla woodland study aimed to trial the effectiveness of cide treatment plots they were present in. the higher ground where the soil is well two herbicides, metsulfuron methyl and Seedling recruits of Viminaria juncea and drained (Keighery and Keighery 1991). chlorsulfuron on S. bulbifera and to inves- Pimelia imbricata var. major were observed With this kind of habitat almost entirely tigate the impacts of these herbicides on in some treatment plots. Of the remaining cleared on the Swan Coastal Plain the co-occurring native species in the Brixton two taxa, Verticordia densiflora fluctuated area is of outstanding conservation value Street Wetlands. in cover across the chlorsulfuron plots (Keighery and Keighery 1991, Gibson while Kunzea micrantha subsp. micrantha et al. 1994). One of the major threats to Methods decreased in cover, across both metsul- the native flora and to the plant com- Trial plots (1 m × 1 m) were laid out in furon treatments and fluctuated across munities of the wetlands is invasion and a randomized block design (control and the controls. Plant Protection Quarterly Vol.18(1) 2003 27 30 in the only treatment plots in which it occurred, metsulfuron methyl (1.0 g ha-1) (Table 1). 25 Observations on reproductive biology 20 and spread Observations over the period of our study have provided insights into some aspects 15 of the reproductive biology of S. bulbifera including seed biology, mechanisms of 10 dispersal and patterns of invasion within Mean number of plants the wetland. Although plants produce small bulbils up the stems as they die 5 down at the end of each season, popula- tions appear to spread mainly by seed. Each plant produces around 75 soft thin 0 papery coated seeds in late spring and control metsulfuron methyl metsulfuron methyl chlorsulfuron within the wetlands at least, water ap- 1.0 g per ha 2.5 g per ha pears to be a major dispersal agent. The seed has been observed floating in stand- Figure 1. Mean number (with standard error bars) of mature Sparaxis ing and flowing water and maps reveal bulbifera plants in treatment plots (1 × 1 m) before (dark) and after (pale) populations moving mainly through low herbicide treatments. lying wet areas including creeks and drains. Sheet water flow occurring across the wetland in winter may well explain 600 small populations of S. bulbifera appear- ing in undisturbed bushland. There is also evidence that human activities are playing 500 a role in the spread of the population with dense infestations occurring along walk- ing tracks. 400 Interestingly the seed appears to be relatively short lived in the soil, gener- ally germinating the first season following 300 ripening. Prolific seedling recruitment was observed throughout populations of S. 200 bulbifera before the management program Mean number of plants of number Mean began. One year following removal of all flowering plants from isolated popula- 100 tions little or no seedling recruitment was observed in those populations. 0 Discussion control metsulfuron methyl metsulfuron methyl chlorsulfuron Effectiveness of treatments and impacts 1.0 g per ha 2.5 g per ha on native taxa It is clear that the herbicides tested all ef- Figure 2. Mean number (with standard error bars) of juvenile Sparaxis fectively controlled S. bulbifera at the trial bulbifera plants in treatment plots (1 × 1 m) before (dark) and after (pale) sites, with metsulfuron methyl at 2.5 g -1 herbicide treatments. ha the most effective. The high number of juvenile plants remaining in the treat- ment plots indicates that there will need to be follow up control and any successful Of the 14 perennial herbs present, eight across all plots it occurred in including management strategy will require a com- taxa retained or increased cover within all controls.