Call for growers to be whitefly aware

Cotton growers and their agronomists are being urged to be on the lookout for the damaging imported pest silverleaf whitefly.

Speaking on CSD’s Web on Wednesday broadcast, CSIRO entomologist Dr Lewis Wilson said hot conditions early in the season may have accelerated population increases, and growers should ensure they check crops for this pest.

“These very warm conditions mean the whitefly will be developing faster and so there will be more generations and the potential risk of outbreaks higher for cotton,” he said.

He said the key strategies were to prevent early population development by controlling weeds on farm, promoting predator and parasite insect populations by careful management of other pests, and effectively sampling silverleaf whitely, beneficial populations other pests and the plant to assess damage..

According to Dr Wilson, populations of the pest are very evident in home gardens in towns in the Namoi Valley but growers had done a good job in controlling the plants on-farm that carry the pest from season to season and this may help to reduce survival of the pest.

“There’s always gardens and water in the towns so the population just ticks over there. Once you move out of the town onto the farms themselves, we’ve done limited sampling, but it shows that a lot of the growers have kept their farms clean so weed numbers are down,. Nevertheless, silverleaf whitefly are starting to be found so it is important for growers to consider how to approach management of this pest” he said.

Promoting insects that feed on silverleaf whitefly, particularly microscopic parasitic wasps, is an essential part of keeping pest populations in check and the secret to this, according to Dr Wilson, is not killing these good bugs when spraying other pests.

“All the evidence we have says beneficial insects have the most impact on pests such as whitefly when the densities are low – especially through the early part of the season,” he said.

“If you can maximise mortality of silverleaf whitefly in the cotton then populations will not increase so quickly. That’s the way to avoid having a problem, and it’s good risk management,” he said.

“It means when growers are managing pests such mirids, they need to establish if mirids need to be controlled, which requires good sampling to estimate their abundance and to look at fruit retentions levels and if mirid numbers are low and fruit retention is high they probably don’t need to be controlled and this reduces the risk of spraying and disrupting beneficial populations,” he said.

“If you do find a spray is warranted, you should start off as selectively as you can and particularly avoid the pyrethroids and organophosphates. These products have a high risk of reducing beneficial insects, including parasites, and this could lead to whitefly becoming a problem requiring expensive options later on,” he said.

Dr Wilson said a whitefly sampling and threshold technique had been developed by Dr Richard Sequiera from DEEDI in Queensland that could be used by growers and agronomists to collect information to make an informed decision on managing the pest.

“Basically this involves presence/ absence scoring throughout the crop and I’d recommend all the consultants and agronomist should familiarise themselves with that the sampling technique,” he said.

They should start reasonably early and become familiar with silverleaf whitefly sampling and with identify which whitefly species they have. Growers uncertain about species can send samples to Dr David Murray or Zara Ludgate (DEEDI, Toowoomba) for identification. The technique was also linked to thresholds for deciding if and with what to control the whitefly” he said.

Dr Wilson said information about silverleaf whitefly sampling, thresholds and suggestions for mirid controls that were less damaging to predator insects is available in the 2009-10 Cotton Pest Management Guide, available for the Cotton Catchment Communities CRC or at http://www.dpi.nsw.gov.au/agriculture/field/field-crops/fibres/cotton/cotton-pest-management-guide

23 December 2009

Further Information: Dr Lewis Wilson 0267 991500