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Harvest weed seed control benefits organic croppers

Organic farmers are the original integrated weed managers. Now, some of the innovations that are being developed to combat herbicide resistant weeds on conventional farms are proving useful for organic farmers too.

Phil and Ashlee Jackson, in partnership with Brad and Jenna Jackson, manage a 400 ha organic farming system at Westmar, southern Queensland, growing wheat, linseed and lablab.

Phil Jackson (left) with brothers Matt (centre) and Brad (right). Phil and Brad manage the organic farm at Westmar Queensland. All three brothers work alongside their parents Peter and Janice on their conventionally-farmed land at Gurley NSW.

Since 2014 Brad and Phil have been developing valuable weed management tactics, such as camera-guided inter-row cultivator, narrow windrow burning and green manuring, that can be employed in both conventional and organic farming systems.

With cultivation being the only real option for summer weed control in organic farming operations Brad and Phil are keen to investigate any options that will help them stay ahead of the weed seed bank.

“Not being able to do any in-crop weed control was a big concern for us,” says Brad. “Three years ago we bought a Garford inter-row cultivator from the UK to use it in our wheat and linseed crops.”

The cameras on the cultivator guide the alignment of the tynes to follow the plant row with an accuracy of just 10 mm. The 500 mm row spacing enables use of the inter-row cultivator, which can be used when the crop is 100 to 400 mm high.

The camera-guided inter-row cultivator allows in-crop weed management until the crop reaches about 400 mm in height.

“We use it mainly to control wild radish and wild oats,” says Phil. “It suits our 12 m controlled traffic farming system and there is no reason why we couldn’t also use it strategically in our no-till conventional farming operation at Gurley, NSW.”

At harvest, Brad and Phil use narrow windrow burning on as much of the area as possible, to collect and burn weed seed present late in the season. They have found this practice a good way to reduce the weed seed bank most years without burning all the stubble.

Narrow windrow burning can be successful in reducing weed pressure in the following seasons, particularly for annual ryegrass.

Phil says it can be rewarding when the conditions are favourable, particularly to control annual ryegrass. “We try to burn as early as is safe to clear the way for cultivation for summer weed control,” he says.

The Jacksons also utilise green manuring – an age-old weed control tactic in organic farming. They have found the summer legume lablab to be a good option for green manure ahead of a long fallow. Lablab produces a dense and competitive crop that prevents weeds from establishing, while also giving the soil a nitrogen boost.

Lablab is a dense, competitive green manure crop that provides excellent ground cover and weed suppression over summer.

The tactics employed in this organic operation tick off all the non-herbicide weed control tactics in the WeedSmart Big 6 promoted as a practical system to combat herbicide resistance. In an organic system four of the six tactics can be broadly applied to reduce weed pressure.

  1. Rotate crops and pastures – The Jacksons’ rotation is simple but effective. Linseed is grown after wheat to control soil borne root diseases including crown rot, common root rot, yellow leaf spot and spot form of net blotch. It is also resistant to both main species of root lesion nematodes. Linseed yields are higher when grown after AMF host crops that maintain high numbers of the arbuscular mycorrhizae fungi (AMF). High performing crops are one of the best ways to combat weeds.
  2. Mix and rotate herbicide MOA – Not applicable on organic farms but very important in systems that use herbicides.
  3. Increase crop competition – High performing winter crops combined with a summer legume green manure crop in rotation.
  4. Use the double knock to preserve glyphosate – Not applicable on organic farms, however, the idea of monitoring weed control efficacy and removing survivors still applies – more crop, less weeds.
  5. Stop weed seed set – Cultivation in the fallow and in-crop (with the guided inter-row cultivator) significantly reduces weed seed set.
  6. Implement harvest weed seed control – The Jackson’s currently use narrow windrow burning to capture weed seed at harvest. They are also looking at other options such as chafflining and impact mills. All the current harvest weed seed control tactics are non-chemical tools that are being rapidly adopted on Australian farms.

More resources:

https://www.youtube.com/watch?v=oYE_k2A7zbI
The Garford guided inter-row cultivator in action (promo video).

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