Silverleaf whitefly

The unusual occurrence of silverleaf whitefly in canola in northern NSW probably reflects the warm temperatures and dry conditions of late May, and should dissipate with the cooler temperatures of June.

 

Where have they been reported?

Some canola crops near Tottenham in the Central West Slopes & Plains district of NSW have recently been inundated with silverleaf whitefly (SLW). The canola was at the 2-4 leaf stage, with plants hosting between 10-30 adult SLW per leaf. Pest numbers continued to grow over the ensuing 2 weeks to the point where SLW were present on most canola crops in the region. No chemical controls were required as the canola plants did not show signs of damage and continued to grow well. Similarly, canola crops (4-6 leaf stage) throughout the Condobolin area of the Central West Slopes & Plains district were consistently inundated with whitefly populations, probably SLW. In both regions, the affected canola crops were within 50 km of cotton fields, which were undergoing defoliation and harvest.

Silverleaf whitefly habits and behaviour

SLW is rarely a pest of winter grains because of it’s warm season habit. In the northern region, large numbers of this sucking pest can retard plants; their feeding removes assimilates from the plant that would normally be distributed into plant growth. SLW can also secrete large quantities of sticky honeydew that interferes with photosynthesis through the growth of sooty moulds.

The three main species of whitefly found in Australian crops, mostly cotton, are the greenhouse whitefly Trialeurodes vaporariorum, and two strains of Bemisia tabaci, silverleaf whitefly (Bemisia tabaci B-Biotype) and the eastern Australian native strain. SLW poses the greatest pest threat because of it’s greater host range, faster reproduction rate, and ability to develop resistance to insecticides. Click here for further information about silverleaf whitefly.

Our advice

Distinguishing the three species without a good microscope is difficult. However, the timing of the arrival of these insects strongly suggests that they are SLW originating from cotton.

The onset of cooler conditions will suppress populations of SLW and control is therefore not likely to be required. In crops that are being impacted by SLW, the use of synthetic pyrethroids is unwise because of the risk of increasing insecticide resistance in the species and because of the impact on beneficial insects that will be suppressing other pest populations. Canopy oil is registered for SLW suppression in cotton at 2%vv, and is registered in canola for diamondback moth control in conjunction with Dipel.

 

* Sources of field reports of silverleaf whitefly

Melina Miles – Entomologist, Queensland DAFF (Toowoomba)

Scott Stoll – Agronomist, AGnVet Services (NSW Central West Slopes & Plains)

Geoff Wray – Agronomist, Geoff Wray Consulting (NSW Central West Slopes & Plains)