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Ag News

Harvest weed seed management

  • By: Farm Tender "Prime"
  • Oct 23, 2017

Harvest is only a few short weeks away from commencing in Victoria, and plans are in place for what could potentially be another reasonable harvest.  

We know that stubble management begins at harvest, but there’s excellent opportunities for weed management as well, and decision making now may impact on weed seed numbers in future years.  

Primary Industries and Regions SA (PIRSA) estimates that weeds cost Australian agriculture more than $4 billion a year.

Evolution of resistant weeds is also having a negative effect on grower’s ability to control and combat weeds in an efficient and effective manner.

We know and understand if the industry continues to use herbicides like glyphosate they will become ineffective, which will be detrimental to the whole industry.

At harvest time options are available to help reduce the seed bank of weeds that mature at similar timings to the crop.

Some examples include cutting the crop for hay, crop topping, narrow-windrow burning, chaff carts, chaff decks, and more expensive options such as the Harrington Seed Destructor.

Over the 2009 to 2011 growing season, BCG investigated the effectiveness of four different weed seed set control strategies with an aim of driving down the seedbank without reducing yields in cereal-intensive cropping systems.

This trial was undertaken as part of the GRDC-funded project ‘improving integrated weed management in conservation farming systems’.

The four management options trialed were chaff-cart, crop topping, hay-cutting and narrow windrow-burning, with the hay-cutting treatment being the best strategy for rapidly reducing ryegrass numbers as a result of reducing the ability of the weed to set seed through early management.

However, this option was the least profitable during these seasons, but reduction in profitability from one year’s hay cutting needs to be balanced against the need to reduce the weed seedbank.

Crop topping in the trial demonstrated that it was highly dependent on weed growth stage, with it best fitting in crops with early maturity or sown early to allow management of weeds using products like glyphosate or paraquat at a time safe for the crop, but before viable seed set has occurred in weeds.

While windrow-burning was not as effective as hay-cutting in this trial, this was due to low yielding crops producing poor windrows and therefore not able to achieve the necessary heat for destroying weed seeds. Growers need to assess the suitability of this method to their system. Recommendations are to cut at beer can height to reduce risk of the burn getting away when it is carried out, but this can still be influenced by the stubble type and conditions under which burning occurs as well. For example, barley tends to burn more readily than wheat and can allow a windrow burn to escape if not done well.

The chaff cart method implemented in the trial was not so effective, however commercially they are an effective measure. Draw backs are knowing what to do with the piles of chaff after collection. They can have some value for grazing, but for dedicated croppers this may be a less enticing option.

All of the above are options that growers can use, but there are also newer techniques that have evolved, which include seed destructors, chaff decks and chaff lining. By concentrating chaff onto tramlines in a controlled traffic system, weed seeds need to try and grow in a hostile environment that regularly gets trafficked, as well as in some cases composting with the concentration of plant material left behind.

Different options will suit different growers, and therefore the advice is to think about what would work more effectively in your farming system.