Tame the green bridge and keep insects at bay

Following recent rains, SARDI entomologists have been surveying green bridge growth and conducting field sampling in several cropping regions to assess potential abundance levels of pests, particularly aphids.

SARDI entomologist Bill Kimber said surveys showed a proliferation of Lincoln weed on Eyre Peninsula in early March, with later reports indicating widespread volunteer canola.

“Despite weed abundance, aphids were not detected in extensive plant sampling in early March,” he said. “In late March, some roadside volunteer canola plants in the Lower and Mid North were found to be colonised with cabbage aphid. 

“Very low numbers of green peach aphid and turnip aphid were also present, and cabbage aphid and GPA were identified from a sample of aphids from the Cummins area at the end of March.”

Mr Kimber said virus testing was conducted on five volunteer canola samples from the Mid North, and beet western yellows virus presence was found in one plant collected at Riverton.

BWYV is vectored into canola by a number of aphid species, with GPA the most efficient.

Removing weeds that host insect pests is being encouraged and already many SA growers have treated paddocks with herbicide. 

“Ideally, herbicide application should be undertaken far enough out from planned sowing dates to remove all green growth from the paddock for at least 14 days before sowing,” Mr Kimber said.  “If spraying is undertaken closer to sowing, aphids that are present on the weeds and volunteers are likely to move from dying plants onto emerging canola.”

Following emergence of canola crops, it is advisable to monitor for the presence of aphids regularly.

When making decisions to treat crops for aphids, monitoring for beneficial insects that predate on aphids should also be undertaken, such as ladybird beetles, hoverflies and Braconid wasps.

“These beneficials, and others that prey on aphids, once established can greatly reduce aphid populations,” Mr Kimber said.

“It should also be remembered that the advent of much cooler weather later in autumn can also dramatically reduce aphid populations.”

The PIRSA website features a PestFacts map – an interactive service that allows subscribers to search and view recent and historical pest report locations across south-eastern Australia.