Skip to main content Accessibility help

Influence of Crop Competition and Harvest Weed Seed Control on Rigid Ryegrass (Lolium rigidum) Seed Retention Height in Wheat Crop Canopies

  • Michael J. Walsh (a1), John C. Broster (a2), Charlotte Aves (a3) and Stephen B. Powles (a4)


Harvest weed seed control (HWSC) is an Australian innovation, developed to target high proportions of weed seed retained at crop maturity by many major weed species. There is the potential, however, that a reduction in the average height of retained seed is an adaptation to the long-term use of HWSC practices. With the aim of examining the distribution of rigid ryegrass (Lolium rigidum Gaudin) seed through crop canopies, a survey of Australian wheat (Triticum aestivum L.) fields was conducted at crop maturity. Nine sites with medium to long-term HWSC use were specifically included to examine the influence of HWSC use on seed retention height. During the 2013 wheat harvest, L. rigidum and wheat plant samples were collected at five heights downward through the crop canopy (40, 30, 20, 10, and 0 cm above ground level) in 71 wheat fields. Increased crop competition resulted in higher proportions of L. rigidum seed in the upper crop canopy (>40 cm). The increase in plant height is likely a shade-intolerance response of L. rigidum plants attempting to capture more light. This plant attribute creates the opportunity to use crop competition to improve HWSC efficacy by increasing the average height of seed retention. Crop competition can, therefore, have a double impact by reducing overall L. rigidum seed production and increasing seed retention height. Examining the distribution of wheat biomass and L. rigidum seed through the crop canopy, we determined that reducing harvest height for HWSC considerably increased the collection of L. rigidum seed (25%) but to a lesser extent wheat crop biomass (14%). Comparison of + and − HWSC use at nine locations found no evidence of adaptation to this form of weed control following 5 to 10 yr of use. Although the potential for resistance to HWSC remains, these results indicate that this will not readily occur in the field.


Corresponding author

Author for correspondence: Michael J. Walsh, I. A. Watson Grains Research Centre, Sydney Institute of Agriculture, University of Sydney, 12656 Newell Highway, Narrabri, NSW 2390, Australia. (Email:


Hide All
Barrett, SCH (1983) Crop mimicry in weeds. Econ Bot 37:255282
Boutsalis, P, Gill, GS, Preston, C (2012) Incidence of herbicide resistance in rigid ryegrass (Lolium rigidum) across southeastern Australia. Weed Technol 26:391398
Broster, JC, Koetz, EA, Wu, H (2013) Herbicide resistance levels in annual ryegrass (Lolium rigidum Gaud.) and wild oat (Avena spp.) in southwestern New South Wales. Plant Prot Q 28:126132
Broster, JC, Walsh, MJ, Chambers, AJ (2016) Harvest weed seed control: the influence of harvester set up and speed on efficacy in south-eastern Australia wheat crops. Pages 3841 in Randall R, Lloyd S, Borger C, eds. 20th Australasian Weeds Conference. Perth, Western Australia: Weeds Society of Western Australia
Diggle, AJ, Neve, P (2001) The population dynamics and genetics of herbicide resistance—a modeling approach. Pages 6199 in Powles SB, Shaner DL, eds. Herbicide Resistance and World Grains. Boca Raton, FL: CRC
Ehret, M, Graß, R, Wachendorf, M (2015) The effect of shade and shade material on white clover/perennial ryegrass mixtures for temperate agroforestry systems. Agrofor Syst 89:557570
Fleet, B, Gill, G (2012) Seed dormancy and seedling recruitment in smooth barley (Hordeum murinum ssp. glaucum) populations in southern Australia. Weed Sci 60:394400
GenStat (2015) GenStat statistical package for Windows 18th Edition. Accessed: April 20, 2018
Gill, G, Poole, M, Holmes, J (1987) Competition between wheat and brome grass in Western Australia. Aust J Exp Agric 27:291294
Gommers, CMM, Visser, EJW, Onge, KRS, Voesenek, LACJ, Pierik, R (2013) Shade tolerance: when growing tall is not an option. Trends Plant Sci 18:6571
Gould, F (1991) The evolutionary potential of crop pests. Am Sci 79:496507
Holt, JS (1995) Plant responses to light: a potential tool for weed management. Weed Sci 43:474482
Kleemann, SGL, Gill, GS (2006) Differences in the distribution and seed germination behaviour of populations of Bromus rigidus and Bromus diandrus in South Australia: adaptations to habitat and implications for weed management. Aust J Agric Res 57:213219
Lemerle, D, Cousens, RD, Gill, GS, Peltzer, SJ, Moerkerk, M, Murphy, CE, Collins, D, Cullis, BR (2004) Reliability of higher seeding rates of wheat for increased competitiveness with weeds in low rainfall environments. J Agric Sci 142:395409
McKinney, KK, Fowler, NL (1991) Genetic adaptations to grazing and mowing in the unpalatable grass Cenchrus incertus . Oecologia 88:238242
Morgan, DC, Smith, H (1979) A systematic relationship between phytochrome-controlled development and species habitat, for plants grown in simulated natural radiation. Planta 145:253258
Morgan, PW, Finlayson, SA, Childs, KL, Mullet, JE, Rooney, WL (2002) Opportunities to improve adaptability and yield in grasses: Lessons from sorghum. Crop Sci 42:17911799
Neve, P, Powles, S (2005) High survival frequencies at low herbicide use rates in populations of Lolium rigidum result in rapid evolution of herbicide resistance. Heredity 95:485492
Owen, MJ, Martinez, NJ, Powles, SB (2014) Multiple herbicide-resistant Lolium rigidum (annual ryegrass) now dominates across the Western Australian grain belt. Weed Res 54:314324
Owen, MJ, Michael, PJ, Renton, M, Steadman, KJ, Powles, SB (2011) Towards large-scale prediction of Lolium rigidum emergence. II. Correlation between dormancy and herbicide resistance levels suggests an impact of cropping systems. Weed Res 51:133141
Radford, BJ, Wilson, BJ, Cartledge, O, Watkins, FB (1980) Effect of wheat seeding rate on wild oat competition. Aust J Exp Agric Anim Husb 20:7781
Smith, H (1982) Light quality, photoperception, and plant strategy. Annu Rev Plant Physiol 33:481518
Vandenbussche, F, Pierik, R, Millenaar, FF, Voesenek, LACJ, Van Der Straeten, D (2005) Reaching out of the shade. Curr Opin Plant Biol 8:462468
Walsh, MJ, Aves, C, Powles, SB (2017) Harvest weed seed control systems are similarly effective on rigid ryegrass. Weed Technol 31:178183
Walsh, MJ, Minkey, DM (2006) Wild radish (Raphanus raphanistrum L.) development and seed production in response to time of emergence, crop topping and sowing rate of wheat. Plant Prot Q 21:2529
Walsh, MJ, Newman, P, Powles, SB (2013) Targeting weed seeds in-crop: a new weed control paradigm for global agriculture. Weed Technol 27:431436
Walsh, MJ, Powles, SB (2014) High seed retention at maturity of annual weeds infesting crop fields highlights the potential for harvest weed seed control. Weed Technol 28:486493
Zerner, MC, Gill, GS, Vandeleur, RK (2008) Effect of height on the competitive ability of wheat with oats. Agron J100:17291734
Zimdahl, RL (2007) Weed-Crop Competition: A Review. Hoboken, NJ: Wiley


Related content

Powered by UNSILO

Influence of Crop Competition and Harvest Weed Seed Control on Rigid Ryegrass (Lolium rigidum) Seed Retention Height in Wheat Crop Canopies

  • Michael J. Walsh (a1), John C. Broster (a2), Charlotte Aves (a3) and Stephen B. Powles (a4)


Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed.