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Don’t risk replanting weeds

It is possible to remove weed seed contamination from farmer-retained planting seed but it requires a high level of care and planning and many farmer-cleaned samples still have a high level of contamination.

Un-cleaned seed samples can contain over 1500 weed seeds per 10 kg planting seed, many of which will be seed from herbicide resistant plants.

Un-cleaned seed samples can contain over 1500 weed seeds per 10 kg planting seed, many of which will be seed from herbicide resistant plants.

From a crop hygiene point of view it is obvious that planting clean seed is the best way to prevent weed seed being sown with the crop. If in doubt the cost of buying certified clean seed for planting pales into insignificance against the cost of controlling weeds in crop or the difficulties associated with a weedy paddock at harvest.

There is more to the story though, as clean seed promotes strong crop establishment and early growth—another key tool to reduce the weed seed bank and to combat the spread of herbicide resistance.

Professional seed cleaning machinery not only removes weed seeds, it also removes small and broken seeds and non-seed contaminants. The removal of these other contaminants increases the chance of the retained seed having a high germination rate and strong seedling vigour. Both these factors will increase the competitiveness of the crop and reduce the likelihood of weeds growing and producing seed.

Large seed size is generally equated to higher germination and vigour so the removal of small crop seeds also helps with weed control. Similarly, the removal of non-seed contamination reduces the risk of insect damage and fungal diseases that can spoil the seed quality during storage. Following the guidelines for safe on-farm storage is also important to protect the viability of the retained seed.

A survey in Western Australia by the GRDC-funded Australian Herbicide Resistance Initiative found that the gravity table method of seed cleaning consistently produces the cleanest seed sample. The AHRI survey found that un-cleaned seed samples can contain over 1500 weed seeds per 10 kg planting seed, which would add extraordinary pressure on the next crop. Sieves alone can bring that number down to about 150 weed seeds per 10 kg and a gravity table reduces contamination to about 25 weed seeds per 10 kg.

A fully automated, continuous flow cleaning and grading plant will remove at least 98 per cent of addage. The complete cleaning and grading process will sort the material by weight, length and width as the grain moves over an air screen then a gravity table to remove impurities and finally through indented cylinders to sort the grain according to size.

Any cleaning of grower-retained seed is beneficial for reducing weed pressure in the next crop. An in-field rotary screen cleaner can be expected to leave an average 80 weed seeds per 10 kg of grain while a gravity table will produce the cleanest sample, leaving an average 20 weed seeds per 10 kg of grain.

Any cleaning of grower-retained seed is beneficial for reducing weed pressure in the next crop. An in-field rotary screen cleaner can be expected to leave an average 80 weed seeds per 10 kg of grain while a gravity table will produce the cleanest sample, leaving an average 20 weed seeds per 10 kg of grain.

Investing in such equipment is not economic to treat planting seed only, however when it is used to treat all grain produced it can be economically viable through saving cleaning costs on delivery and potentially upgrading the overall quality of grain sold to meet premium market requirements.

If a grading table is not an economic option in your business, choosing to have planting seed cleaned by a contractor is definitely worth considering over retaining un-cleaned seed or using sieves alone.

If the seed being cleaned has come from an identifiable area of the farm, then this is a good opportunity to collect weed seed and send it off for testing to find out what herbicides the weeds present at harvest are susceptible to. This will help you prepare in-crop weed management strategies for next season.

Plan ahead for the next seed crop and ensure you harvest seed from the cleanest paddock or the cleanest section of a paddock.

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