Australia
October 28, 2013
COMING into winter harvest, now is the time to plan ahead for summer weed control of feathertop Rhodes grass (FTR).
Department of Agriculture Fisheries and Forestry research scientist Michael Widderick said FTR was an all-too-familiar name to farmers in the north, but it could be effectively managed by applying an integrated weed management (IWM) approach in both fallow and in-crop phases.
“The focus needs to be on running down the weed seedbank and preventing seed set,” Dr Widderick said.
Dr Widderick said the weed could not be reliably controlled with glyphosate, especially after early tillering.
“No single weed management treatment will provide 100 per cent control, so use a variety of tactics, both chemical and non chemical.”
Farmers should determine the treatment type according to the density and distribution across paddocks.
“Spot treatments can be used for scattered or occasional FTR infestations. Target small, non-moisture stressed and actively growing plants to improve the chances of good control.”
IWM strategies to controlling FTR are detailed in a new fact sheet from the Grains Research and Development Corporation (GRDC), including the effectiveness of various control options such as strategic tillage, crop competition and on farm hygiene.
When using chemical control methods for FTR Dr Widderick said several residual herbicides were effective at stopping seeds germinating and plants establishing, and could therefore deplete the weed seedbank.
“Ideally residual herbicides are applied to a clean paddock and rain is received within two weeks of application so the herbicide can move into the surface soil,” he said.
“The double-knock tactic can be effective and there are a number of available options,” Dr Widderick said.
He said Glyphosate (Group M) could be followed between seven and 21 days later by Paraquat (Group L) in a double-knock, with the addition of a grass-selective residual such as Balance to the second knock.
Another option for Queensland growers is a permit initiated by the Northern Grower Alliance (PER 12941), which allows the doubleknock of a Group A herbicide followed by paraquat (Group L) but only in fallows that are to be planted to mungbeans. This permit is effective until August 2016 and is restricted to Queensland growers only.
However, the practise of using Group A herbicides in fallow poses a high risk for resistance to develop so it is vital to only use them as part of a carefully considered IWM plan. For on farm hygiene control in non-crop areas, imazapyr can be used.
“The efficacy of herbicides against FTR drops rapidly when plants are larger than the early tillering stage or are moisture-stressed so spray young plants as soon as possible after rain for best results,” Dr Widderick said.
“Always sow crops into weed-free conditions and delay sowing of summer crops in paddocks with a high density of FTR.
“As FTR germinates at or very near the soil surface, burying the seed below 5cm will prevent germinations.
“Strategic soil disturbance is another option. One pass with a harrow has been shown to reduce the number of seedlings emerging by about 90 per cent compared to zero-till.”
“The majority of FTR seeds lose viability after seven to 12 months, which means that although FTR is a difficult weed to manage, if seed production can be limited over one or two seasons then it can be brought under control.”
• The GRDC’s Feathertop Rhodes Grass Fact Sheet is available at www.grdc.com.au/GRDC-FS-FeathertopRhodesGrass
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