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Trifolium dasyurum L. (Eastern star clover): Exploiting a novel pasture species for innovative strategies to control weed seed banks.

Angelo Loi1, Bradley Nutt1 and Clinton Revell12

1 Department of Agriculture and Food Western Australia, 3 Baron Hay Court, South perth WA 6151.
2 Centre for Legumes in Mediterranean Agriculture, University of Western Australia, Crawley, WA 6009.
www.agric.wa.gov.au Email: aloi@agric.wa.gov.au, crevell@agric.wa.gov.au, bnutt@agric.wa.gov.au

Abstract

Trifolium dasyurum (syn formosum), is a species endemic to eastern Mediterranean regions. It has been studied and subject to selection in Australia and is being considered for commercial release. The proposed cultivar has a powerfully expressed delayed germination. The differential germination pattern allows an opportunity for selective removal of early germinating weeds. This strategy was tested in 2003 on regenerating swards of T. dasyurum and Dalkeith subterranean clover (T. subterraneum) at Bakers Hill Western Australia. A non-selective herbicide treatment was applied one month after the break of the season. T. dasyurum regenerated densely after the herbicide application compared to the subterranean clover control. Weed densities were substantially reduced as a result of the herbicide treatment with almost complete control of broadleaf weeds. The delayed germination in T. dasyurum offers farmers a new opportunity to control weeds during the pasture phase compared to currently used pasture legumes that germinate rapidly at the break of season.

Key words

Pasture legumes, delayed germination, weed control, eastern star clover

Introduction

In the Mediterranean-type annual-cropping regions across southern Australia it is estimated that up to $1,033 million per year is spent on controlling crop weeds. High frequency of cropping combined with the continuous use of selective herbicides, has resulted in the development of herbicide resistant weed populations and declining levels of soil fertility. Prevention of production of weed seed in a pasture phase is one option for controlling herbicide resistant weeds populations. Eastern star clover (Trifolium dasyurum), developed through the National Annual Pasture Legumes Improvement Programme (NAPLIP), is a new pasture species with attributes that specially fit this role. T. dasyurum germinates much later in the growing season compared to current pasture legumes and weeds and it may provide farmers with a novel tool to help manage herbicide resistant weeds in a pasture phase. Other traits expressed by the species include high levels of dry matter and seed production and ability to be harvested with conventional combine harvesters. It is suitable for use on mildly acid and alkaline soils with fine texture in low and medium rainfall areas (350-500 mm). Most pasture legumes germinate soon after the break season (at the same time as the weeds) and selective weed control is difficult. Other pasture phase weed control techniques such as spraytopping with non selective herbicides or intensive grazing can be an effective method for preventing weed seed set; however it can also seriously reduce legume seed production. Delayed germination of the desirable species provides a window of opportunity to use non-selective herbicides for control of weeds prior to its emergence. For Santorini serradella, germination appears to be delayed by 10-14 days and spread over four to five weeks. Interestingly, a number of leading farmers growing Santorini have reported spectacular success in controlling weeds with non-selective herbicides after the break of season without compromising spring biomass production (Taylor and Revell 2002). This paper reports on the potential use of T. dasyurum as another species for the management of grass and broadleaf weeds in the pasture phase.

Material and methods

Swards of T. dasyurum (Australian Trifolium Genetic Resource Centre accession 95GRC39das) and Dalkeith subterranean clover (T. subterraneum) were established in 2003 at Bakers Hill, Western Australia (Norman et al. 2005). The average annual rainfall for the site is 594 mm, with an average of 73 mm in May, 114 and 116 mm in June and July, 86 mm, 61.9 and 33 mm in August, September and October. An average of 15 mm a month is usually recorded during the summer. In 2004 a non selective herbicide (glyphosate 540 g a.i./ha) was applied to half of each of the four fully randomised replicate swards (each 0.5 ha) on the 27 of May (5 weeks after the first germinating rains). Ten soil cores (8 cm diameter) were collected for each replicate/treatment (nil and sprayed) 4 weeks after sprayed. Seedlings were separated from the soil and counted into sown legume (T. dasyurum and Dalkeith subterranean clover), grasses and herbs.

Results

Table 1 summaries the plant densities after the spray treatment. The density of T. dasyurum was only moderately reduced by the herbicide treatment compared to subterranean clover (35% reduction compared to 97%). Weed densities were also substantially reduced after the herbicide treatment, particularly the herb component and were similar for both pasture legumes. The grass component was manly represented by ryegrass (Lolium rigidum) and silver grass (Vulpia spp.) the herbs were manly cape weed (Arctotheca calendula) and erodium (Erodium spp.).

Table 1. Plant densities of T. dasyurum, Dalkeith subterranean clover and weeds in unsprayed and sprayed treatments (standard errors in parenthesis).

 

Sown legume

Grasses

Herbs

 

plants/m2

plants/m2

plants/m2

T. dasyurum Unsprayed

722 (135)

6325 (3615)

3548 (939)

T. dasyurum Sprayed

475 (84)

165 (32)

0 (0)

       

Dalkeith Unsprayed

5160 (992)

5295 (3152)

3682 (443)

Dalkeith Sprayed

161 (30)

145 (61)

4 (3)

       

Conclusion

The strategic use of non-selective herbicide in regenerating pasture containing T. dasyurum significantly reduced weed density whilst still retaining a high legume density. In this experiment glyphosate was used as the method of weed control. However, other non-selective weed control such as cultivation or very intensive grazing could be used.

The delayed germination in T. dasyurum offers farmers an important opportunity to control weeds during the pasture phase compared to traditional pasture legumes that germinate rapidly at the break of season.

Acknowledgments

The project has been conducted through the National Annual Pasture Legume Improvement Program supported by Grain Research & Development Corporation (GRDC) and Australian Wool Innovation (AWI).

References

Norman HC, Masters DG, Rintoul AJ, Wilmot MG, Jayasena V, Loi A, Revell CK (2005). The relative feeding value of a new pasture legume, eastern star clover (Trifolium dasyurum), compared with subterranean clover (Trifolium subterraneum). Australian Journal of Agricultural Research 56, 637-644.

Taylor GB, Revell CK (2002). Seed softening, imbibition time, and seedling establishment in yellow serradella. Journal of Agricultural Research 53, 1011-1018.

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