Unusual insect activity reported in emerging crops

The combination of early season rainfall and warm autumn temperatures is likely to have triggered widespread insect emergence and migrations.

Entomologists at the South Australian Research and Development Institute (SARDI), the research division of Primary Industries and Regions SA (PIRSA), have received significant reports of different caterpillar species being detected in and impacting crops.

Weed web moth caterpillars have been reported on the west coast at Streaky Bay and across the northern Eyre Peninsula at Cleve, Buckleboo, Kimba and Waddikke, according to SARDI entomologist Rebecca Hamdorf, who co-ordinates the PestFacts SA newsletter through a Grains Research and Development Corporation (GRDC) investment.

“Native budworm has been reported on volunteer peas, cereal and canola on EP at Wudinna, Minnipa and Streaky Bay, and on medic at Kimba,” Ms Hamdorf says. “Cutworm caterpillars have been detected in canola at Wudinna and Kimba.

“Notable flights of multiple moth species have occurred at Streaky Bay as well as Bordertown, Naracoorte and Sherlock in the South-East.”

It is possible that caterpillars and other pests such as aphids have transferred from a green bridge of weeds, volunteer cereals and native vegetation into emerging crops.

Ms Hamdorf says it can be challenging to correctly identify caterpillars due to their similarities in appearance. To support growers and advisers with identification of these pests, PestFacts SA provides free identification to subscribers – for more information visit https://bit.ly/2MlzTSJ.

Meanwhile, leafhoppers have been reported on canola at Whyte Yarcowie and Eudunda in the Mid North. Numbers in both areas are described as high, and they are visibly jumping off plants when disturbed. The movement and colour can look similar to lucerne flea, but they are more elongated and larger.

“Some small feeding damage from the leafhoppers has been recorded as whitish necrotic spots on the cotyledons,” says SARDI entomologist Maarten van Helden.

“Warm condition favour leafhoppers, so cooling temperatures means they are unlikely to persist for much longer.”

PestFacts SA has also received reports of Russian wheat aphid (RWA) activity near Loxton East (Murraylands), southern and upper EP, Kadina on Yorke Peninsula, at various locations in the Mid North including Whyte Yarcowie, east of Eudunda and Everard Central, Padthaway in the South-East and at Myponga Hill (Fleurieu Peninsula).

Dr van Helden says treatment of RWA should only be considered if infestations are at potentially damaging levels.

“Australian intervention threshold recommendations are currently based on overseas research, which recommends a spray application when more than 20 per cent of all seedlings are infested with aphids up to growth stage 30 and more than 10 per cent of tillers are infested with aphids from growth stage 30,” Dr van Helden says.

He says while growers may observe a lot of tillers with symptoms (the cold weather enhances symptom expression), very few of these tillers are likely to have aphids present.

“It is important to make the distinction between tillers with symptoms and tillers with aphids,” Dr van Helden says.

Aphid populations are not expected to increase now due to the onset of cold and wet weather.

Through research investments by the GRDC, being led by SARDI and research organisation cesar, a biological and ecological profile of RWA is being developed to provide Australian grain growers with scientifically robust management tactics for the future, including economic thresholds for Australian farming systems.

A RWA resource portal which includes updates on current research efforts and the latest RWA management advice, hosted by cesar, is available at http://bit.ly/2Px67tu.

In the meantime, SA growers and advisers are encouraged to report to PestFacts SA (https://bit.ly/3eyp8bU) any detections of invertebrates (pest/beneficial/unknown) in crops and pastures.

For more information about crop pests, see the latest PestFacts SA newsletter on the PIRSA website at https://bit.ly/36PHti5. A range of pest identification and management resources can be found at https://bit.ly/3crpSy1.

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