Lessons learnt: crop-seed cleaning reduces weed-seed contamination in Western Australian grain samples

In this work, AHRI researcher Dr. Mechelle Owen surveyed and quantified weed seed infestation of the crop seed that farmers would be planting. In Australia, farmers save their own crop seed (wheat, barley, pulse crops, non-hyrbid canola) for planting in the subsequent growing season. Farmers produce their saved crop seed on low weed burden crop fields, so as to minimise weed seed contamination. This survey was done in 2015. This is the third AHRI survey, with the first conducted in 1998 (Powles & Cawthray 1999) and a larger second survey in 2009 (Michael, Owen & Powles 2010). In this third survey in 2015, Mechelle Owen surveyed 81 crop seed samples, each of 10 kg crop seed (wheat, barley, canola, lupins).

The crop seed that farmers plant at crop seeding time needs to be of high quality and ideally should be completely free of contaminating weed seeds. If there is contaminating weed seed, then planting this weed seed at crop seeding efficiently delivers weeds into cropping fields. This contaminating weed seed can introduce into crop fields existing and new weed species and herbicide-resistant weed seeds. The great majority of WA farmers utilise commercial seed cleaning contractors to remove weed seed from their crop seed. Commercial seed cleaners mostly utilise gravity tables to remove contaminating weed seed. The objective is to minimise weed seed contamination of crop seed (to minimise weed seed being planted at crop seeding).

This survey established the very encouraging result that 41% of the crop seed samples had zero weed seeds! Thus under normal commercial conditions, it is possible to have weed-free crop seed. Before commercial seed cleaning the average number of weed seeds was 184/kg crop seed. Gravity table seed cleaning reduced this weed seed number to 1 seed/kg. Clearly, commercial gravity table seed cleaning removes nearly all weed seed from crop seed.

59% of the crop seed samples contained some weed seed contamination. As expected, annual ryegrass Lolium was the major weed seed contaminant and it was nearly always multiple herbicide-resistant. Wild oat Avena, wild radish Raphanus and Brome Bromus were the other principal weed seed contaminants.

This research shows that farmers can ensure that they do not plant seeds of very dangerous weed species into crop fields. They can ensure zero to very low weed seed contamination by growing their crop seed on low weed burden fields and then ensuring that the subsequently harvested crop seed is commercially cleaned (gravity table). This is an integrated weed management technique to minimise weed and herbicide resistance issues. It is very pleasing that, as a result of these three AHRI surveys conducted since 1998 and associated communication with farmers and agronomists, farmers have reduced the amount of weed seed infesting their crop seed and thereby have reduced “planting” weed seed with their crop seed.