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Aphids

Reports of aphids are slowly subsiding although populations are still very high in many areas. Continuing developments with resistance and viruses warrant close attention.

 

Cereal aphids

Very large numbers of cereal aphids have been holding back wheat and barley crops in the Swan Hill – Ultima area of the Victorian Mallee. Aphid numbers have continued to increase through early-mid June. Some crops in the region, which are generally at the 3-leaf to mid tillering stage, have been infested with 10-20 aphids per plant and have warranted chemical control.

Near Hopetoun, also in Victoria’s Mallee, cereal aphids have been identified as placing a number of wheat and barley crops under stress. The prominent aphid populations were on 2-leaf to tillering stage crops. While the crops lacked vigour, it may have been the combined influence of aphids and prior heavy infestations of earth mites and lucerne flea. Barley crops east of Inglewood in Victoria’s Northern Country have had unprecedented infestations of cereal aphids that are also reported to be holding back crops. Initial attempts to control the aphids with omethoate appeared ineffective.

Refer to PestFacts Issue No. 3 for further information on cereal aphids.

Aphids in canola and legumes

Aphids are still causing issues in canola and some pulses, particularly in the Victorian Mallee. In crops around Manangatang, high numbers of green peach aphid (Myzus persicae) are causing plant damage and have required chemical control. Cowpea aphids (Aphis craccivora) have been identified on vetch and lentils near Hopetoun, while there is still some concern about aphids, probably green peach aphid, in pulse crops near Swan Hill. In all cases, aphids are being closely monitored and controlled when necessary. High densities of canola aphids have been also been found on volunteer canola within wheat crops near Conargo in the NSW Riverina. Fortunately these aphid species do not tend to transfer across cereals, and wheat crops are progressing well. We have also received several reports of green peach aphids from canola crops in South Australian.

In several cases (in SA and Victoria) growers have failed to control green peach aphid populations after applying several applications of insecticides. Resistance to synthetic pyrethroids, organophosphates and pirimicarb is widespread in this species. Aphids from several localities have been collected and will be tested for resistance to multiple chemistries. There is evidence that these insecticides will still be successful in many situations, but not all.

Victorian DEPI have undertaken virus testing in canola samples from Eudunda, SA, and found very high (83-100%) incidence of BWYV (beet western yellows virus) in the 4 samples tested. Assuming this is true across wider regions, this suggests that there is now little point in controlling aphids for virus control alone.

See earlier issues of PestFacts for further information on green peach aphids and cowpea aphids.

Our advice

In the situations where aphids have been present for many weeks (and the risk of initial virus infestation has passed), insecticide use is only justified when populations are seriously compromising crop performance. Remember, aphid numbers will begin to decline with the onset of cold conditions. In cases were sprays are needed, the use of ‘softer’ insecticides such as pirimicarb and sulfloxaflor should be considered. Please note, pirimicarb is more effective if applied when temperatures are above 20°C. Broad-spectrum insecticides, particularly synthetic pyrethroids, are lethal to populations of beneficial insects which will increase the risk of further pest flare ups (aphids and caterpillars) in early spring.

 

* Sources of field reports of aphids

Greg Dearman – Agronomist (Victorian Mallee)

Peter Harris – Grower (Victorian Northern Country)

Frank Henry – Grains Pathology Team, DEPI Horsham (Victorian Wimmera)

Peter Hopper – Agronomist, Hooper Consulting (SA Mid North)

Sean Krahnert – Agronomist, Elders (Victorian Mallee)

Andrew McMahen – Agronomist, Landmark (Victorian Mallee)

Sam Trengrove – Consultant (SA Mid North)

Justin Whittakers – Agronomist, Landmark (NSW Riverina)

Kent Wooding – Agronomist, AgriVision (Victorian Mallee)

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