Soil predatory mites which have the potential to control onion thrips in onions and significantly reduce reliance on chemical treatments for the devastating pest have been identified in a research project led by Industry & Investment NSW.

“We have found that onion thrips infesting red onions in storage can be effectively managed by innundative releases of the soil predatory mite Neoseiulus cucumeris,”  said I&I NSW entomologist Jianhua Mo.

“This is the first report in the world of successful biological control of onion thrips in storage onions.

“The mite is commercially available and the cost is relatively low, making it an attractive control option.

“The same technique can also be used to control onion thrips in storage brown onions.

“We have also demonstrated the potential of another soil predatory mite, Hypoaspis aculeifer, for controlling onion thrips in the field.”

The findings are part of a new I&I NSW project that is developing integrated management strategies (IPM) against Onion thrips - the most important insect pest of onion in Australia.

Onion damage from thrips includes yield loss, skin blemishes, contamination of onion bulbs and transmission of disease, in particular Iris Yellow Spot Virus (IYSV).

Jianhua Mo said the new IPM strategy would reduce insecticide resistance and reliance on persistent chemicals for thrips control.

“In most years onion thrips populations build-up in onion fields from small localised invasions rather than mass invasions from afar followed by population growth within onion fields.

“The likely sources of local invasions are volunteer onions and weed hosts in the surrounding vegetation.”

As a result of the project, the following IPM strategies are recommended for controlling onion thrips in onions:

• Reduce source populations of onion thrips through (a) reduction of volunteer onions by removing all onion bulbs in the soil during harvest; (b) timely disposal of onion culls; and (c) removing large patches of weeds on the farm.
• Use insecticides only when action threshold is exceeded and rotate chemicals from different chemical groups.
• When infestation is of concern in storage onions, apply cucumeris mite mix to top of the bins at a minimal rate of 0.25 L/bin. The mite mix is available from Biological Services (http://biologicalservices.com.au).

Also resulting from this and previous projects, two new chemical control options, lambda-cyhalothrin and spirotetramat, have become available to Australian onion growers for controlling onion thrips.

Registrations of the two insecticides have ended the industry’s reliance on organophosphate insecticides.