The Department of Agriculture, Western Australia is working with the State’s horticulturalists to promote better crop management to prevent an increase in insecticide resistant pests.

Over the winter period, the Department identified two different species of whitefly in the Carnarvon region that have become resistance to insecticides.

Department senior entomologist Darryl Hardie said silverleaf whitefly (Bemesia tabaci  Biotype B) had been found on cucurbit crops and the greenhouse whitefly (Trialeurodes vaporariorum) on tomato and capsicum.

“The resistance build up in the case of the greenhouse whitefly, was a result of poor insecticide usage locally,” Dr Hardie said.

“The silverleaf whitefly, an exotic pest, had already developed a resistance to insecticide in Australia and overseas before being detected in Carnarvon.

 “The ability of a minor or non-pests such as whiteflies to build a resistance to insecticides shows a new pest scenario can be expected in the future, unless management strategies are introduced.”

Dr Hardie said when growers were developing and introducing an integrated pest management strategy they should consider several options.

“These include growing crops which mature early or at times when the pest is not present, minimising their crops’ exposure to the target pest and using insect-resistant crops where possible,” Dr Hardie said.

“Only applying chemical if it is economically justified, rotating chemical groups used to control pests to prevent a resistance build-up, rotating crops to allow the most time possible between crops and creating pest barriers such as windbreaks or bare earth barriers should also be considered.”

Dr Hardie said whiteflies caused damage when present in large numbers.

“They produce honeydew on which sooty mould develops, they transmit damaging plant viruses and their feeding can affect plant growth, causing distortion, discolouration and yellowing or silvering of leaves,” Dr Hardie said.

“Varied management strategies, to assist in the control of whitefly, are being extended to Carnarvon growers by local Department research officer Amanda Annells.

“Options for growers include removing the whitefly’s favoured habitat including host weeds and abandoned crops to interrupt the breeding cycle, spraying and conserving natural enemies including parasitic wasps, lacewing larvae, lady beetles and hoverfly larvae.

“If growers choose to spray, they must first identify the species of whitefly as each requires different chemical management. Spraying must provide excellent coverage of the plant as whitefly hide under leaves and within the plant canopy.” 

Growers can contact the Department’s Carnarvon office on 9956 3333 for ‘Ag Flash’ information on controlling whitefly.

Other factsheets are available from Department offices or from the website www.agric.wa.gov.au

Search for Farmnote 35/2004 ‘Silverleaf whitefly Bemisia tabaci (Biotype B) with reference to related whiteflies in Western Australia’, Gardennote 5/2004 ‘Whitefly’ and Farmnote 30/93 ‘Western flower thrips’.