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Fighting herbicide resistant weed with serradella pasture
South Perth, Western Australia
May 3, 2004

Cadiz serradella pasture can play an important role in the fight against herbicide resistant weeds such as wild radish and annual ryegrass, according to Western Australia Department of Agriculture pasture specialist Keith Devenish.

“Cadiz French serradella has been the catalyst in offering short term pasture phases to bring weed populations back under control with two main sowing systems evolving”, Mr Devenish said.

“The major change is the ability for farmers to grow and harvest their own serradella seed for less than 50 cents a kilogram and being soft seeded, the Cadiz can be inoculated and sown as a cleaned header sample.”

One system is to dry seed Cadiz pasture early, followed by grazing with sheep to keep weeds down during the growing season and then brown manure the whole stand with glyphosate ready for cropping again.

Mr Devenish said one tool used with this system was tactical or crash grazing early in the season while feed is limited and sheep have to eat everything on offer, including the weeds.

This system suits a one-year pasture phase that is desiccated at the end of the season so that no weeds set any seed and the nitrogen breaks down quicker for the next wheat or canola crop.

The second sowing system is to sow Cadiz for two years by sowing after the normal cropping program when several germination’s of weeds can be spayed out and farmers with own their supply of cheap seed can sow double the normal seeding rate of Cadiz.

Grazing and spray topping with paraquat are used in the first year and then glyphosate in the second year to desiccate and brown out all the weeds in spring.

Mr Devenish warned that a two-year pasture system does have a risk of failing in the second year with about a 40 per cent chance the Cadiz will have poor regeneration due to normal weathering of the soft seed.

“This just means growers need to monitor closely at the start of the second season and be flexible enough to change plans and sow a grain crop or re-sow the paddock to Cadiz”, he said.

“On the other hand, I have seen Cadiz germinate in February after summer rain and be tough enough with its deep root system to persist much longer than other annual pastures until normal winter rains, allowing it to grow well into October and November giving green feed for 10 months,” he said.

“While ryegrass is reasonably easy to control in the system, wild radish still causes some issues with about 70 percent of serradella stands having to be sprayed for wild radish.

“Spray grazing for radish control is a great tool for sub-clover pasture but is not an option with serradella so herbicides like Broadstrike, Raptor or Spinnaker have to be used”.

“Better still are the blanket wiper machines where high chemical concentrate can be wiped onto wild radish at less than 50 cents a hectare for herbicide costs and the wiper equipment can be towed behind a 4WD ute.”

Other non-chemical options such as cutting serradella hay, mowing and grazing are important and an early shallow cultivation (tickle) before sowing pasture followed by a knockdown reduces weed burden considerably.

A blanket wiper machine is ideal for targeting taller weeds like wild radish in the fight against herbicide resistant weeds.

In one paddock where the farmer had a crop failure from herbicide resistant ryegrass, he used an early tickle to encourage the weeds, grazed throughout the first season with eight sheep per hectare and spray topped paraquat twice in spring to stop all weeds setting seed.

He then seeded Cadiz in the second year, grazed with sheep again, desiccated the stand in spring with glyphosate and then it was successfully sown back to wheat in the third year used trifluralin to control what ryegrass was left.

My Devenish said the commercial release of two new hard-seeded French serradellas, Erica and Margurita, offer some more options and he will be conducting trials with farmers in Jerramungup and Ravensthorpe to test new ideas.

The recently released farmnote 62/2003 “Serradella – growing and harvesting the seed” explains the agronomic management and how to harvest several varieties of serradella seed can be accessed from the Department’s website at www.agric.wa.gov.au

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