The Leaflet June 2012

CRICHTONA — Wed, 27 Jun 2012 22:26:08 +0000

The Leaflet May 2012

CRICHTONA — Tue, 01 May 2012 00:41:41 +0000

The Leaflet February 2012

CRICHTONA — Tue, 28 Feb 2012 22:54:41 +0000

The Leaflet December 2011

CRICHTONA — Mon, 19 Dec 2011 23:51:19 +0000

The Leaflet November 2011

CRICHTONA — Tue, 08 Nov 2011 04:37:03 +0000

The Leaflet September 2011

CRICHTONA — Mon, 05 Sep 2011 05:35:49 +0000

Phosphine still a killer in cooled grain

CRICHTONA — Thu, 30 Jun 2011 00:30:29 +0000

Warm winter days can provide highly fertile conditions for insect pests, especially in southern Queensland and northern New South Wales where toasty temperatures provide an ideal breeding ground for stored grain pests.

With more growers storing grain on-farm to take advantage of a deregulated grain market, stored grain insects have become a greater problem in recent years. Increased on-farm storage is contributing to, and suffering from, growing insect resistance to the industry’s main fumigant, phosphine.

Most grain in Australia is harvested in the warmer months in conditions that can lead to heat-damaged grain and mould; conditions that are favourable to insect pests. To combat this many growers aerate stored grain, to reduce grain temperatures to 20°C or less.

Although lower temperatures maintain grain quality and reduce insect population growth, industry researchers have questioned whether phosphine is as effective at actually killing insects in grain stored at a cooler temperature.

Now, Queensland Department of Employment, Economic Development and Innovation entomologist Dr Greg Daglish and research development agronomist Philip Burrill have determined that phosphine can still be effective at lower temperatures, within certain parameters.

Over a number of years and using both laboratory trials and trials with on-farm silos, they found that phosphine is generally less effective at lower temperatures; but in the right conditions, that is, in a properly sealed, gas-tight silo and with adequate exposure periods, phosphine fumigation of cool grain to control resistant insect populations is possible.

“The benefits of cooling and phosphine fumigation are that cooling preserves grain quality and reduces insect population growth, and phosphine kills insects and has a residue-free status in all major markets,” Dr Daglish says. “The work has proved that cool grain fumigation is an option for growers and meets market needs.”

However, changing temperatures do affect some phosphine-resistant strains of key pests. Dr Daglish says that although the most resistant Australian strains of two pests are known to respond similarly to phosphine, the project showed that one species became much harder to control in cool grain.

It is an important finding for an industry reliant on phosphine to treat stored grain for pests, and where these pests are becoming more resistant to it.

Mr Burrill says the majority of tools growers had for dealing with grain pests 10 to 15 years ago are falling over. “The only thing we can say to growers is that having a well-constructed, aerated and sealable silo gives you the option to fumigate with phosphine, which when done correctly is still effective against all our pests.”

The ‘cool grains’ work, which started as a Grains Research and Development Corporation project, has also highlighted some vital information about phosphine and its interaction with stored sorghum.

For example, an early finding relates to sorghum’s sorption rate (how quickly it absorbs phosphine), which influences fumigation performance. Generally sorghum is more sorptive than wheat.

“It means that when it comes to phosphine fumigation in sorghum, there is less margin for error than for, say, stored wheat, so fumigations need to be spot on,” Dr Daglish says.

Sorption is the major cause of phosphine loss in well-sealed silos. However, in cooled wheat or sorghum, the sorption rate is lower at lower temperatures, meaning that higher concentrations will be achieved for longer.

Another discovery, that older grain tends to be less sorptive, means that delaying fumigation could also help keep phosphine concentrations higher for longer.

Although results for silo trials varied, three general observations were made about phosphine concentrations: lower concentrations tended to be measured deeper in the grain mass; lower concentrations tended to be measured on silos’ northern sides; and concentrations measured higher in the grain mass tended to peak earlier.

Dr Daglish says aluminium phosphide tablets must not be mixed with the grain itself, so tablets are often placed on trays in the silo headspace. When phosphine gas is liberated from one point it takes time to diffuse throughout the whole grain bulk, so gas concentrations are not always distributed uniformly in all parts of the storage.

“It is essential that sufficient time is allowed to ensure maximum gas distribution, to achieve the best results from phosphine fumigation,” he says.

The Leaflet July 2011

CRICHTONA — Wed, 29 Jun 2011 23:48:59 +0000

The Leaflet May 2011

CRICHTONA — Wed, 04 May 2011 05:36:11 +0000

The Leaflet February 2011

CRICHTONA — Thu, 24 Feb 2011 05:23:41 +0000

CRC for Plant Biosecurity - leaflet