Bushland Weeds Manual - Environmental Weeds Action Network

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14 Chapter 3 Grass Weeds • Transition occurs when the growing points stop producing vegetative material and start developing flowers and the tissue between nodes, the internode, elongates. Because of internode elongation, slashing or mowing at this stage can remove many axillary buds, thereby reducing leaf production in the regrowth. • Flowering begins when the seed head is just emerging from the leaf sheath (boot stage) and continues through to seeding. Some grass-selective herbicides are only effective if applied prior to the boot stage. Slashing or mowing during flowering may facilitate the spread of seed. The period of active growth depends largely on whether the plant is a cool season (C3) or warm season (C4) grass. Cool season and warm season grasses differ in the way they use carbon dioxide. Cool season grasses (Wild Oat, Blowfly Grass, Perennial Veldgrass) photosynthesise more effectively, and thus are most actively growing, during the cooler periods of winter and spring (15-25° C). Warm season grasses, or summer grasses, photosynthesise best with full light saturation and consequently their period of most active growth is late spring and summer (25-40° C). The summer growing Couch (Cynodon dactylon), Kikuyu and Lovegrass are all C4 grasses. For successful herbicide uptake grasses should be sprayed in the season appropriate to their photosynthetic pathway and when actively growing. Fire and the spread of grass weeds Many grasses, especially caespitose species, have long, narrow, vertical leaves that are efficient in strong light allowing sunlight to penetrate deep inside the clump (Gibbs Russell et al. 1991). This structure allows the production of a large biomass in a small space. Stems die each year and new ones develop. Over time a large biomass, much of it dead material, creates a significant fire hazard. As a result, grass weed invasions can lead to changes in fire frequency and intensity. These changes are self-perpetuating as the disturbance caused by fire tends to promote germination and establishment of seedling grasses (Cheplick 1998, Williams and Baruch 2000). At Shenton Bushland, Perth, Perennial Veldgrass was mapped in the year following an intense fire that burnt half of the site. A comparison between a pre-fire bushland condition map and the post-fire Veldgrass map, highlighted a significant post-fire expansion in the population. Previously healthy bushland now recorded 75-100 % cover of Veldgrass (Brown and Marshall unpublished data). Fire contributes greatly to grass invasion in lownutrient soils, where post-fire increases in nutrients, light and space availability are more effectively exploited by invasive grasses than by the native flora. It is important to reduce the possibility of fire in bushland areas at risk of grass invasion. Where bushfire does occur target resprouting plants and seedlings for control before they become established. Management and control Prevention and early intervention Degradation of our native bushland remnants through clearing, fire, disease and mismanagement may be of particular relevance to the establishment and spread of grass weeds. Often an observed decline in the canopy cover within Banksia woodlands around Perth correlates with an increase in the occurrence of Perennial Veldgrass. Reduction in canopy cover leads to an increase in light availability, a condition favoured by many grass weeds (Williams and Baruch 2000, D’Antonio et al. 2001). Weed grass invasion can be limited by: • Maintaining the bushland canopy. Many grasses prefer open sunny sites and do not establish or compete successfully in the shade. • Reducing the potential for bushfires. As mentioned, fire can significantly increase the establishment and spread of grass weeds. • Identifying unfamiliar grasses. It is important to determine if grasses are introduced or native. Early identification of grass weeds allows you to assess the likelihood of invasion and prevents mistaken eradication of native grasses! • Establishing weed barriers. Weed barriers A common grass weed problem in urban remnants is the spread of Kikuyu, Couch or Buffalo Grass (Stenotaphrum secundatum) from adjacent parks and road verges. A successful ‘weed break’ can be created by embedding a physical barrier such as weed mesh or conveyor belt vertically into the ground and using concrete kerbing above it. This prevents rhizomes creeping into the bushland and provides a mowing edge for council mowers (Box 3.4). Some grasses have rhizomes 50 to 60 centimetres below ground and any root barrier must allow for this. The bush itself often provides an excellent weed break (Box 3.2). However, the sandy soils and open vegetation of Banksia woodland or the friable soils of York Gum–Jam woodlands are more susceptible. Establishing a dense cover of locally-occurring low, medium and tall shrubs along the edges of degraded sites and paddocks could act as a sieve, preventing entry of wind and water carried seed. Knowing the prevailing wind direction, position in the landscape and relationship to waterflow can help to determine if the adjacent paddock, weedy rail reserve or over-run, semi-rural backyard, is the weed source. When planting or direct seeding, use native seed collected from the area of bushland you are protecting and only plant where run-off or prevailing winds are definitely carrying weed seed in.
Box 3.4 Spread of turf grass at Blue Gum Lake Chapter 3 Grass Weeds At Blue Gum Lake in the City of Melville, parkland often adjoins bushland. In most of these sites Couch (Cynodon dactylon) and Kikuyu (Pennisetum clandestinum) have been planted as turf. On one boundary between turf and bushland a large infestation of the woody weed Geraldton Wax (Chamelaucium uncinatum) was removed. The site revegetation project was undertaken by the Friends of Blue Gum Lake who were continually faced with Couch that kept creeping back from the grassed area. After spraying the Couch several times an alternative solution was sought. Creating a physical barrier by using kerbing, was an attractive option. Kerbing was multipurpose: It provided a neat and tidy mowing edge which pleased the local residents and council, prevented the incursion of mowers into the bushland and also limited the spread of Couch. Several stories were circulating regarding the use of rubber conveyor belts buried into the ground vertically and used as barriers to stop rhizome and stolon spread. When a pre-used conveyor belt was donated by Wesfarmers, and the Lotteries Commission agreed to provide funding for the above-ground kerbing, the project was underway. An outline was created using a rope and marked with stakes. Making an early start, the City of Melville Bushland Works Crew, an enthusiastic Work for the Dole crew and EWAN project officers dug the trench, lay and buried the one metre wide conveyor belt. On several occasions there was grateful acknowledgment that the digging was in sand. In all, it took twelve people four hours. The only hiccups were several large Banksia roots, which were dug around, and the conveyor belt cut to fit. A contractor was brought in to do the kerbing, providing the finishing touch. With the donation of the conveyor belt, the labour or in-kind support, the project cost $1164 for 100 metres of barrier – this was all in the kerbing contractor’s fees. While the amenity grass already in the revegetation area still needs to be controlled, once it is eradicated it should be an easier job to keep new incursions out! 15
Page 1 and 2: Bushland Weeds A practical guide to
Page 3: Acknowledgments This manual is the
Page 6 and 7: iv Introduction The Banksia, Tuart
Page 8 and 9: 2 Chapter 1 The Project Blue Gum La
Page 10 and 11: 4 Chapter 1 The Project Both Arum L
Page 12 and 13: 6 Chapter 2 Managing Weeds in Bushl
Page 14 and 15: 8 Chapter 2 Managing Weeds in Bushl
Page 16 and 17: 10 Chapter 3 Grass Weeds Many grass
Page 18 and 19: 12 Chapter 3 Grass Weeds Box 3.3 Gr
Page 22 and 23: 16 Chapter 3 Grass Weeds Control te
Page 24 and 25: 18 Chapter 3 Grass Weeds Rhizomatou
Page 26 and 27: 20 Chapter 3 Grass Weeds Case Studi
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Page 38 and 39: 32 Chapter 4 Corms, Bulbs and Tuber
Page 58 and 59: Chapter 4 Corms, Bulbs and Tubers W
Page 60 and 61: Iridaceae Moraea miniata Two Leaf C
Page 62 and 63: Chapter 5 Broadleaf Herbs, Sedges a
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64 Chapter 5 Broadleaf Herbs, Sedge
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Chapter 5 Annual Broadleaf Herbs, S
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Chapter 5 Annual Broadleaf Herbs, S
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Chapter 5 Perennial Broadleaf Herbs
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Chapter 5 Perennial Broadleaf Herbs
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74 Chapter 6 Trees, Shrubs and Clim
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Chapter 6 Trees, Shrubs and Climber
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Chapter 6 Trees, Shrubs and Climber
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90 Chapter 7 Weed Mapping in Remnan
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92 Chapter 7 Weed Mapping in Remnan
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94 Chapter 8 Herbicide Use in Bushl
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100 Final Note In the end, environm
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102 References 1 Aarssen, L.W., Hal
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104 References 101 Dixon, B. (2002)
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106 References 204 Mann, R. (1998)
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108 307 The Nature Conservancy (200
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