Farmers are being urged to watch for cowpea aphids after they were detected in crops north of Kadina last month.
The insects were found on volunteer lentil plants acting as a green bridge prior to crops emerging.
YP AG agronomist Chris Davey said farmers were monitoring aphid numbers across the region. Northern Yorke Peninsula was a high-risk area as it had high rainfall in April and farmers sowed early, but drier areas – which were sown later – between Kadina and Curramulka were not as vulnerable.
Mr Davey said the insects sucked the sap out of lentils and caused the plant to wilt or, in extreme cases, die.
This may be a threat in 2017, given the lack of forecast rain for the growing season and the need for plants to keep the moisture up to their leaves.
“They also spread viruses such as cucumber mosaic virus, bean yellow mosaic virus and alfalfa mosaic virus due to their sap-sucking means of eating. If the aphid is carrying a virus, they transfer the virus to the new plant,” he said.
Mr Davey said farmers relied on selective or non-selective insecticides to manage the issue once a lentil crop was sown. He encouraged selective aphid sprays rather than non-selective options to allow beneficial insects to survive, and keep control of any future infestations of cowpea or blue-green aphids.
Cowpea aphid is a widespread pest commonly found on legume and pulse crops, including field peas, lupins, lentils, faba beans, lucerne and medics, and are capable of being transported on the wind large distances, particularly during autumn.
They tend to colonise single plants before moving onto surrounding plants to form dense colonies on groups of infested plants in ‘hot spots’ within a crop.
In pulse crops damage can result in yield losses of up to 90pc in susceptible varieties, and up to 30pc in varieties with intermediate resistance.
Initial signs of damage include yellowing or whitening of leaf veins, with high numbers causing rapid wilting of leaves and eventually plant death.