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When is clean, clean enough with Mechelle Owen

Retaining seed on-farm for planting next season makes good economic sense, unless that seed is contaminated with weed seed.

Mechelle clean seed



AHRI researcher, Mechelle Owen, says many growers are unaware of the level of weed seed contamination that can occur in crop seed retained for planting, even after cleaning.

AHRI senior research officer, Mechelle Owen, surveyed grower-retained seed to assess the level of weed seed contamination and the effect of grain cleaning. What she found alarmed the growers involved and pointed to the importance of sowing clean seed into clean paddocks.

“The first finding was that the vast majority of the surveyed growers retained seed for planting and were conscious of the need to remove weed seed contaminants,” she says. “Unfortunately, over 70 per cent of the seed samples we analysed were still contaminated with weed seed, even after cleaning.”

The remaining samples were weed-free, proving that attention to detail can produce a clean sample suitable for planting.

The other finding was that much of the weed seed collected at harvest time is herbicide resistant. “Growers would never deliberately plant herbicide resistant weed seed along with their crop,” says Ms Owen. “But that is what happens if the retained seed is not thoroughly cleaned. Many weeds present at harvest are there because they are herbicide resistant.”

WS-contaminated seed

Planting crop seed contaminated with potentially herbicide resistant weed seeds will increase the in-crop weed pressure.

How much contamination is too much?

Short answer: Every weed sown has the potential to return seed to the seed bank.

Longer answer: 100 weed seeds per kilo of cereal or pulse seed sampled equals around one weed per square metre when the crop is sown.

Does the type of cleaning system used make a difference?

Short answer: Yes, gravity tables are best.

Longer answer: The growers surveyed used a range of cleaning methods including gravity tables, sieves, combination and rotary screen cleaners. Combination and rotary screen cleaners produced a similar level of decontamination, sieves provided the poorest result and grading tables gave the best results. Crop type also influenced the level of weed seed contamination, with greater weed seed contamination in cereal samples compared to lupin samples. Any cleaning is beneficial but the more professional the better as independent contractors consistently achieved cleaner seed.

How do I measure the level of contamination?

Short answer: Check a 1 kg sample.

Longer answer: Collect a 1 kg sample of the retained seed and separate the crop seed from all other material.

What’s the best way to reduce or avoid weed seed contamination?

Short answer: Harvest seed from paddocks with minimal weeds.

Longer answer: Plan ahead. Clean grain harvesting and handling gear thoroughly between paddocks. Harvest seed from low-weed-burden paddocks and use a gravity table clean the seed. Check the level of contamination after grading.

How to ask a WeedSmart question

Ask your questions about planting clean seed to help manage herbicide resistant weeds, using Facebook, Twitter @WeedSmartAU or leave a comment below.

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