New moves against black oats keep odds in growers favour

Combating black oats has been a constant chess game for northern New South Wales and southern Queensland croppers, however, some new moves in recent times, including using different chemistry groups of knockdown and residual herbicides, are at least keeping the odds in growers’ favour.

Tony Lockrey, Consulting Agronomist at Moree with AMPS Agribusiness, which strongly invests in independent production research in the region, has been dealing with increasing Group A fop resistant black oats in the district for the last 10 years.

Tony said the use of Group A herbicides had been widespread within the popular wheat-chickpea rotation in the region.

“Products that were the safest on the crop, cheapest and most active have been pushed hard and are now less effective,’’ Tony said.

“Group A resistant black oats forced consultants and growers to look to new modes of action and herbicide groups for knockdown control in crop, as well as revisiting some of the residual treatments that had been neglected due to the adoption of zero tillage.

“Growers have since been using Atlantis® and, to a lesser extent, Hussar® and Crusader® herbicides and growing more Clearfield® wheat and barley in their systems. After 10 years, some of the earliest farms that converted to Clearfield crops are now finding IMI-resistant phalaris. This highlights the need to rotate modes of action and herbicide groupings to prolong the life of our existing chemistry. Integrated weed management is a must.’’

He said the only way to sustainably tackle the weed resistance problem was to assess the whole farming system, including crop choice and rotation sequence, to maintain profitable cropping whilst not letting any seedset occur.

“Every lever we can pull to attain this outcome is explored. This has and will include knockdown and residual chemistry, agronomic, genetic, cultural and mechanical solutions where needed.’’

Tony said while wheat was the traditional mainstay in crop rotations and pulses, oilseeds and summer crops were used to manage key diseases such as crown rot and nematodes, rotation plans must also work to provide the best possible control of problem weeds and prevent their seedset for a minimum of three years, helping to relieve pressure on systems.

“We take stopping seedset so seriously that we will spray out wheat pre-harvest with glyphosate to stop viable seedset by late germinating black oats, or even slash or plough down problem patches that have escaped control. Unfortunately, weed seed destructors and windrow burning are less effective on black oats than ryegrass, as early germinated plants have often dropped their seed prior to harvest. Baling crop areas for stockfeed is another alternative to stop seedset.’’

He said the use of Group B selective herbicides in wheat, particularly Atlantis, was picking up black oats that emerged in crops when used correctly.

Reinforcing the notion of wearing out products that are cheaper, soft on crops and easier to use, Tony cautioned that Atlantis must be used in the right situation at the right time – then it was very effective.

“It is critical that both the crop and weeds targeted are at the right growth stage and in good condition. Get that right and the Atlantis control can be very good, even on high weed populations,’’ he said.

“Be very careful to avoid spraying stressed weeds and crop, particularly frost stress that is recent or imminent, as weed control results may disappoint and transient crop checking may occur.’’

Tony recommended using water rates of around 100 L/ha and twin tip nozzles for good coverage of the target, as well as using oil, rather than wetter, with Atlantis.

“While oil may cause some slight spotting on the crop, I think it gives the optimum job.”

“Always use the full rate in good conditions and the results will follow.’’

In terms of residual chemistry, he said in some cases farmers had returned to applying Treflan® with Avadex® Xtra prior to sowing, hoping to reduce in-crop weed pressures, but their re-adoption was not widespread due to poor performance and incompatibility with the zero tillage/minimum tillage system.

Tony said use of the newer Group K pre-emergent herbicide, Sakura® 850 WG from Bayer, with Avadex Xtra on a ryegrass area in wheat had been a “fantastic brew’’ and, in combination with a follow-up Atlantis spray in crop, a fallow and a dryland cotton crop, the paddock had since cleaned up extremely well.

“The field treated had 90-100 ryegrass plants per square metre, with multiple herbicide resistance the previous year in Clearfield canola, as well as black oats and some scattered barley grass in the headlands,’’ he said.

“While it was a risk to take it to wheat, the stubble cover was required to fallow out to the following cotton crop, so it was decided to tackle the weed burden head-on with well incorporated residual herbicides, as well as the strategic in-crop selective.’’

The field was planted to a short season wheat after the initial ryegrass emergence had been double knocked.

In addition to suppressing black oats and great brome, Sakura, which contains the active ingredient, pyroxasulfone, controls annual ryegrass, barley grass, silver grass, annual phalaris and toad rush in wheat (not durum wheat), triticale, chickpeas, field peas, lupins and lentils.

Tony said the new label additions for Sakura made it a “standout candidate’’ among the soil-applied residuals to investigate and use well in systems.

“There is a lot of room for growth with Sakura because we are not using residuals very much and we need to be exploring every possibility to limit the number of grass weeds emerging in crops – as a starting point to eliminating seedset,’’ Tony said.

“Sakura is taking 50-80% of black oats out in trials and upwards of 80% of ryegrass. It must be used wisely in the rotation however, as it should not be used more than twice every four years.’’

He said Sakura was more robust in a variety of conditions, particularly more stable than other residuals in dry conditions following planting, which often occurred.