Management tips for mites in cotton

Cotton growers are being urged to be on the lookout for mites in cotton following reports of increased populations this season.

Speaking on CSD’s Web on Wednesday broadcast, CSIRO entomologist Dr Lewis Wilson said he was aware of mite populations in crops in central Queensland, St George, the Macintyre Valley and southern New South Wales.

Dr Wilson said management of mites is relatively straightforward because there are well established sampling strategies and thresholds for deciding when control is required.

“Mite management is highly dependant on good monitoring and sampling. Its best to take a series of mite samples because the effect that mites have on yield depends on when they start increasing and how quickly they increase.”

“By doing the sampling over a couple of dates, the rate of population increase can be calculated and used to estimate the likely yield loss which helps decide if it is worthwhile controlling the mites,” he said.

Dr Wilson said the sampling technique was very simple and could be done when inspecting the crop for other pests such as aphids and silverleaf whitefly.

“Basically it’s presence absence sampling – you inspect leaves at the top of the plant, about the fourth or fifth leaf below the terminal and score if they’re infested with mites or not – if they’ve got any stage of mite on them they are classed as infested and if they’re clean they’re not infested,” he said.

While several effective options are available to control mites, Dr Wilson said good management of weeds to avoid encouraging mites was an important first step.

“Mites need food plants to survive on through winter and can be commonly found on many of the weeds on cotton farms so weedy fields will have a higher risk of carrying mite populations from one cotton season to the next.”

“In spring when the winter hosts die off, the mites get blown onto or crawl onto new hosts, so if they are on a weeds in or on the border of a cotton field, they could move onto the cotton,” he said.

“There are also quite a few predators that will eat mites – most of the lady beetles and predatory bugs eat mites and thrips in particular are great predators of mites. When predators are in the crop, they will slow the mite population down so you need to do everything you can to keep them,” he said.

“If pest populations need controlling, some of the available insecticides are quite selective, meaning they control the pest but have less effect on the predators, which can then help control mites. In contrast, some insecticides are quite disruptive and will kill most predators which allows mite populations to increase unchecked – this includes the older organophosphates and pyrethroids.”

Dr Wilson said detailed instructions on mite sampling and thresholds were available in the Cotton Pest Management Guide, available online at http://www.dpi.nsw.gov.au/agriculture/field/field-crops/fibres/cotton/cotton-pest-management-guide.

12 February 2010

Further Information: Dr Lewis Wilson 0267 991550

Above: Maintaining populations of predator insects such as striped lady beetle in cotton crops is important in managing mites.