Eastern rains trigger weeds explosion

Neil Lyon October 29, 2018

Grass weeds will be a challenge to control in a year when there will be substantial sorghum plantings. (Photo: WeedSmart)


WIDESPREAD rains across the eastern farming zone over the past few weeks have set the scene for a big summer crop planting – and triggered an outbreak of weeds that farmers are now working to contain.

Dalby Rural Supplies head agronomist, Andrew Johnston, said conditions had turned around dramatically on the Darling Downs after a long dry period that had limited winter crop production.

Mr Johnston said 2018 had been one of the driest years on the Downs in a very long time, but it had been the wettest October some areas had seen for decades.

“There will be a massive sorghum plant go in now. Cotton will go in after that in early November. They are also gearing up for some late corn and late mungbeans in December/January, depending on late rainfall.

“There is a huge population of weeds. They have sat for the last eight months and done nothing. We have a big flush of spring and summer weeds, and even have some winter weeds coming up that didn’t germinate through winter.”

Mr Johnston said there was a wide range of emerging weeds, particularly feathertop Rhodes grass, fleabane, milk thistle and barnyard grass.

It would be the grass weeds that would present the biggest challenge to growers this year.

“Grasses will be a big issue this season given the increased planting of sorghum. There will probably be paddocks go into sorghum that didn’t get planted to winter crop that probably shouldn’t be (going to sorghum) because of the grass populations. But given the sorghum market at the moment there will be sorghum go in everywhere,” he said.

“There will be a lot of double knock (herbicide strategies) applied. There is a lot of pre-plant glyphosate and 2,4-D going on, then post-plant pre-emergent there will be a lot of paraquat, atrazine and Dual going on. Atrazine will control the broad leaf weeds, Dual will give residual control on the grasses and the paraquat will give a double knock on the fleabane, feathertop Rhodes grass and barnyard grass.”

Take no prisoners

Grains Research and Development Corporation (GRDC) crop protection officer north, Vicki Green, said it would be a challenge for growers to manage the flush of weeds this season.

Vicki Green

“Everyone wants to sow summer crops. But if you can delay sowing so you can get a knockdown herbicide on the weeds before, then put a residual product on so you are not relying on just one control mechanism alone, that is the ideal,” she said.

“The optimum is to try to get a weed germination then control it. But that is more easily said than done.

“Because the rain has been so patchy, and if you have different soil types, you have different weeds coming up on different soils. It is not easy, but the key is for people to be vigilant and monitor their paddocks.”

Australian Herbicide Resistance Initiative (AHRI) northern extension agronomist, Paul McIntosh, called for growers to try to maximise their chances of a total weed kill to stave off the threat of herbicide resistance.

“I urge people to carry out their weed control pre-plant and aim for no survivors from that weed-spraying operation. That way we can get a run on reducing herbicide resistance. Herbicides resistance extends once there are survivors,” he said.

Sorghum seed shortage

In other summer cropping issues, Mr Johnston said a shortage of sorghum seed would impact some growers, particularly those looking to plant later in the season.

“The growers and companies who ordered early have been able to meet their requirements, but the issue will be with any late planting. Growers on the western Downs haven’t had significant rain yet. The issue will be their optimum sowing time tends to be late December/January and it will be a real issue getting seed,” he said.


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