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

For many years, AHRI senior researcher Michael Walsh led AHRI research on harvest weed seed control (HWSC) techniques. That AHRI research and communication on HWSC has helped HWSC become widely adopted by Australian grain growers.

Michael is now Professor and Director of the Weeds Research Program at the University of Sydney, with responsibilities across a large area of north-eastern Australian cropping.

HWSC is effective in that L. rigidum seed is retained (non-shattering) to the plant (and other seed retaining weed species) within the standing mature grain crop and HWSC enables seed capture at grain harvest time and subsequent destruction.

The obvious evolutionary reality is that persistent use of HWSC is a selection pressure for any mechanisms enabling L. rigidum (annual ryegrass) seed to avoid HWSC. For example, seed shatters before grain harvest or a greater percentage of retained seed at a height below that at which the crop is cut in the harvesting operation.

In this latest paper, Walsh et al at several sites confirmed that the majority of retained L. rigidum seed at grain harvest will be captured. This was true in crop fields in which HWSC had been conducted for several years.

Please note that we are NOT stating that plants cannot evolve resistance to HWSC. Indeed, everything that herbicide resistance has taught us is that plant populations will respond to any persistent, effective selection pressure. Importantly, this study showed that a good, competitive wheat crop meant that L. rigidum responded with taller plants, meaning that retained weed seed was relatively high in the canopy and thus captured by HWSC. This shows the yield and weed control advantages of having a good, competitive high yielding crop. A healthy, competitive crop, HWSC and diversity in methods of weed control are key to sustainable systems!