Dirty seeds a threat to export markets

Australian Herbicide Resistance Initiative (AHRI) senior researcher Mechelle Owen and senior lecturer in agriculture at Curtin University, Pippa Michael, carried out a survey to see how growers could better control their weed management programs.

The research found contaminating weed seed in 73 per cent of the crop seed which farmers had planned to plant within the next couple of years, ryegrass was the most prevalent weed seed found and as expected it displayed multiple herbicide resistance.

Sowing clean seed was an essential component of weed management and could prevent the further introduction of weeds into WA farming systems.

The study looked at the weed seed contamination of cleaned grain and herbicide resistance levels of the recovered weed seeds on 74 farms throughout WA's grain-growing area.

On the surveyed farms most farmers grew and conserved their own crop seed.

The survey found that even the majority of cleaned samples had some level of seed contamination by up to 11 kinds of foreign weed and volunteer crop species at an average of 62 seeds every 10 kilograms of grain.

Ryegrass was the most common contaminant in all samples but wild radish, brome grass and wild oats also featured heavily.

When the samples were categorised by crop type, ryegrass was by far the most frequent contaminant of all cereal crops and wild radish was the most frequent in lupins.

Uncleaned crop seed samples had about 25 times more contamination than cleaned crop seed.

The study also found that herbicide resistance was highly prevalent in the ryegrass populations found in cleaned grain except for glyphosate which controlled all the populations tested.

The study confirmed that many growers were unknowingly introducing substantial levels of weed and volunteer crop seeds into their farming systems at seeding even though crop seed-cleaning techniques had been used.

Although the level of weed seed contamination perceived by farmers was comparable to the survey results, actual seed numbers were much higher than perceived by the farmers surveyed which showed that they were severely underestimating the amount of weed seed contamination.

In the paddocks the level of weed seed contamination equated to 465 foreign seed contaminates a hectare based on an average seeding rate.

The study demonstrated that herbicide-resistant ryegrass populations were usually maintained at about the same low densities as susceptible populations, however if these weeds were not managed then each plant would produce up to 500 seeds which were then returned directly back into the farming system.

The study showed that 27pc of surveyed farmers had weed-free crop seed but it was unlikely that weed seeds could be completely removed by cleaning.

This meant other factors like field abundance and crop hygiene were highly likely to have an influence on weed seed contamination levels.

It was suggested that the timing of weed seed dispersal might be an important factor which influenced the number of contaminants within crop seed.

WA certified wheat was allowed to contain up to 15 foreign seeds and a maximum of one volunteer crop seed per kilogram of grain.

This meant planting certified seed may still introduce weed seeds into the farming system which only emphasised the importance of cleaning grain using the most effective techniques prior to seeding.

International trade could also be a way for weed seed invasions into new habitats.

Many weed seeds had been shown to be introduced by grain trade and could have significant impacts on the new ecosystems.

This could cause major economic losses for agricultural industries as well as affects on markets for grain traded to other countries.

If grain traded between Australia and other countries was found to contain herbicide-resistant weed seeds it could have potentially devastating effects for Australian export markets.

Coincidentally, but completely independently, in Japan recently a group worried about the importation of weed seeds sampled wheat shipments coming in from WA.

Without fail they found that ryegrass was contaminating WA wheat shipments arriving to their country.

The Japanese delegation then tested for herbicide resistance and found high numbers of herbicide resistance in the ryegrass.

AHRI senior researcher Mechelle Owen said there were four main things that growers needed to take away from the research.

"The first is that growers can achieve a clean crop seed sample and that any sort of seed cleaning method is better than not using any cleaning methods at all," she said.

"Secondly growers should be aware that they could be sowing herbicide-resistant weed seeds onto their farms and this could be a source for continue weed problems.

"Crop hygiene is important to help keep weed numbers low and grain contamination could have potential threats to export markets particularly if herbicide resistant which is something no grain grower wants to hear."