With the potentially destructive silverleaf whitefly moving from summer to winter vegetable crops throughout the Lockyer Valley growers are being asked to use non-chemical control methods where possible to help protect their industry.

Gatton-based Department of Primary Industries and Fisheries insect ecologist Brendan Nolan said growers were finding silverleaf whitefly in early winter crops like Brassicas and lettuce, with early indications of rapidly increasing numbers.

He said because these insects were able to develop tolerance to insecticides it was important for growers to switch from insecticide reliance to effective and sustainable management practices to control silverleaf whitefly.

"Silverleaf whitefly is now well established in the region and it's up to growers to work together to reduce its impact in the Lockyer," he said

Mr Nolan said silverleaf whitefly and heliothis were the major insect pests of vegetables, with the whitefly causing particular concern because of the rapid development of insecticide resistance and a lack of new products for its control.

He said silverleaf whitefly (Bemisia tabaci biotype B) was a pest of more than 500 crop plant species many of which were major vegetable crops in the Lockyer Valley.

"Insecticides are an important part of a silverleaf whitefly management program but they do have limitations.

"The fact is that there are few effective insecticides for silverleaf whitefly management due to limited crop registrations combined with the added threat of insect pest resistance if chemicals are overused.

"Broad-spectrum insecticides are disruptive to beneficial insects and so can exacerbate problems," he said.

Mr Nolan said to offset the limitations of insecticides growers could use a range of non-chemical approaches.

"Awareness of silverleaf whitefly on properties is very important and can be gained through regular monitoring of susceptible crops. This allows growers to make rational decisions on the need for control.

"For example you might have silverleaf whitefly in your crop but beneficial insects are suppressing their population growth so no control is needed."

He said communication and collaboration between growers and across industries were important parts of a management strategy.

This included removing all farm weeds and volunteer crop plants like silverleaf whitefly hosts that included slender celery, sow and milk thistle, fat hen, bellvine and common morning glory, spurge, deadnettle, bladder ketmia and anoda weed, apple of Peru, wild gooseberry and glossy nightshade, and purple top and lantana

Other options Mr Nolan suggests are:

• where possible allow a host free period for the pest by planting non-host crops such as maize or sorghum during summer;
• where possible plant younger susceptible crops some distance away or up-wind from mature crops
  destroy host crop residues immediately after harvest;
• optimise water management to avoid moisture stress, which increases silverleaf whitefly severity and honeydew production;
• preserve beneficial insects (wasps and ladybirds) by avoiding broad-spectrum insecticides, particularly synthetic pyrethroids and organophosphates.

Vegetable growers can contact Mr Nolan at the DPI Research Station at Gatton (5466 2222) for more information or to discuss silverleaf whitefly and its management.