Australia
December 8, 2015

An integrated management strategy is growers’ best line of defence against the rapidly escalating problem of feathertop Rhodes grass.

The most successful approach is likely to include a combination of tillage, crop choice, crop competition, residual herbicides and the selective use of double knock applications in fallow.

CEO of the Northern Grower Alliance (NGA), a Grains Research and Development (GRDC) funded grower solutions group, Richard Daniel (pictured) said commitment to very high levels of control over a 12 -18 month period can exhaust the seed bank in the soil.

“Feathertop Rhodes grass can be a very aggressive weed once established but the longevity of seed viability is actually quite brief,” he said

”Feathertop Rhodes grass may again be a problem following the wet end to harvest in the north this year, as research shows us it is often one of the first weeds to establish on bare ground following rainfall events in spring and summer.

“Research by the Queensland Department of Agriculture and Fisheries has shown it can germinate on small rain events, even as little as 10mm, with peak germination at 2 days.”

Control of established populations of large feathertop Rhodes grass is difficult, extremely costly and generally incompatible with zero till farming, so the focus must be to to keep it out of farming paddocks wherever possible but be ready to respond to new incursions very rapidly, Mr Daniel said.

“Knockdown herbicides can be an effective tool for control, however results are very dependent on favorable application conditions together with weed stage and size,” he said.

“Glyphosate alone will rarely provide effective control and, even when followed with a double knock of paraquat, the levels of control are generally unacceptable.

“Research trials have shown that some Group A herbicides can be effective against feathertop Rhodes grass, however they must be followed by a paraquat double knock to ensure a high level of control and minimise weed escapes.’’

Weed growth stage is critical to the performance of Group A herbicides, with small, non-stressed weeds controlled more effectively. These herbicides are rarely effective against mature plants.

Mr Daniel said that Group A herbicides were also one of the quickest modes of action to select for resistance as there was typically a higher frequency of resistant individuals in the natural population.

For this reason, he said all applications in fallow must be followed by a double knock, targeted at small weeds only, and used no more than once per season.

“Many Group A herbicides also have plantback restrictions for subsequent cereal crops and this needs to be considered when selecting potential control methods,” he said.

“To date we have not found any herbicide treatment that provides consistent control of mature plants with growers often forced to consider ‘salvage’ cultivation.

“This may also be the most effective strategy to allow herbicides to more successfully be used to manage subsequent germinations.”

Residual herbicides have proven to be an important component of the most successful control strategies. Balance® can be an effective option for fallow management due to its residual control of feathertop Rhodes grass combined with activity against fleabane, common sowthistle and awnless barnyard grass.

”The key point though, is that any single tactic approach is generally unsatisfactory and that for effective control growers need to use a combination of tools that suit their farming system. An integrated approach is generally the only way to successfully control feathertop Rhodes grass,” Mr Daniel said.
 

Website: http://www.grdc.com.au

Published: December 9, 2015