GRAIN growers in southern and northern cropping regions need to keep an eye on their crops over coming weeks as warmer spring conditions may promote flights of Russian wheat aphid (RWA).
RWA numbers have been minimal so far this season, due largely to low survival rates over the hot and dry 2018-19 summer.
Higher temperatures in spring may lead to an increase in aphid migration, but scientists say crops older than growth stage (GS) 40 do not appear to be attractive to migrating RWA, therefore colonisation of such advanced crops during spring is unlikely.
Rare cases of RWA presence and symptoms, below intervention thresholds, have been reported this year by growers and advisers in areas such as Victoria’s southern Mallee and East Gippsland, as well as the New South Wales Riverina, Central West Slopes and Plains, and the Central Tablelands.
Entomologists involved in Grains Research and Development Corporation (GRDC) research investments say economically significant yield impacts are more likely from infestations that occur before stem elongation, but only if these persist during the later (heading and flowering) stages.
South Australian Research and Development Institute (SARDI) entomologist, Maarten van Helden, said detecting RWA in crops was not difficult as indications of infestation were usually quite obvious.
“A tell-tale sign is white or purple leaf streaking in cereal crops. And at late tillering and during stem elongation, leaf rolling may occur,” Dr van Helden said.
Growers should search for the presence of aphids by peeling back rolled leaves, since symptomatic tillers do not always contain aphids and therefore treatment may not be required if the aphids have either moved on or died.
First identified in Australia in 2016, RWA is now present in many cropping areas of SA, Victoria, Tasmania and NSW. The aphid has not been detected in Western Australia, the Northern Territory or Queensland.
RWA distribution is expected to move northwards again this year to northern NSW and possibly southern Queensland.
Since RWA has only been confirmed in Australia in recent years, limited research under local agro-climatic conditions and farming systems has been conducted.
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