Protect yourself: sealed silos slow resistance

Photo of Silos

PHOSPHINE USE in farm storages is under threat from high-level insect resistance.

Unless growers en masse improve their phosphine use practices, by applying it only in well-maintained, sealed storages, the situation will deteriorate. Phosphine use in unsealed storages will select for increased levels of resistance, while use in properly sealed storages gives exposure rates sufficient to kill all resistant strains of insect. This was a key message for growers from researchers speaking at the recent Post-harvest Technical Conference in Canberra.

Used in Australia for the last 45 years, phosphine is low-cost and, when used properly, leaves no residues and kills insects effectively. Unfortunately there is widespread improper use, with many growers using phosphine in unsealed silos. According to research entomologist witb Queensland's Department of Primary Industries (QDPI) Pat Collins, "there's no doubt that under-dosing selects forresistance. Using phosphine in unsealed storages exposes large numbers of insects to closes tbat kill susceptible insects but allow resistant insects to survive and multiply.

"This new resistance had us worried; we weren't sure whether growers would be able to control it. However, recent research, undertaken by Chris Newman of the WA Department of Agriculture, Greg Daglish of QDPI, and Barry Wallbank of NSW Agriculture, has shown that the dose rates and lengths of exposure obtained in sealed farm storages are sufficient to kill all life stages of all resistant strains - but the storages mnst be sealed."

Even sealed silos not foolproof

To complicate matters, many sealed silos are not properly maintained. They leak, thus reducing the period of time that lethal concentrations are present. With little field data available, researchers wanted to investigate what is actually happening in grower-operated storages. The researchers conducted trials in 19 sealed silos in three states.

Silos were (where necessary) re-sealed, prior to pressure testing, using standard rubber sealing strips available from any industrial rubber supplier. In all silos, the preliminary inspection revealed leaks in the seals at tbe inlets and outlets or low oil in the pressure relief valve.

Phosphine was used at a rate of 1.3-1.5 g/m3 using aluminium phosphide tablets in a tray suspended in the headspace. The concentrations of phosphine were recorded at varying depths in the silos using electronic phosphine monitors.

Pressure tests of the farm bins gave half-life results ranging from I second to 6 minutes. The recommended standard for gas-tightness is a test result of 3 minutes for a full silo or 5 minutes for an empty or partially-full silo.

Monitoring of gas concentrations during fumigations revealed that, of the 11 silos that met the 3-minute pressure test standard, all maintained concentrations of phosphine that would control all resistant insects.

Maybe you don't know all there is to know about phosphine

Recent research conducted by the Phosphine Awareness Extension Group has shown tbat growers generally don't seek advice on the use of phosphine. The information to use phosphine correctly is on the container label but, because it has been around for so long, a degree of familiarity has crept in and it is treated casually.

It is vital for the Australian grain industry to retain this valuable, highly effective and low-cost fumigant, but continued resistance development and the chance of an accident involving human life put it at risk.

Growers should seek training in appropriate use of phosphine for on-farm fumigation and at least two courses are available to them. Chemcert has a module ready to go, as does Farm Information Services in WA. Growers can also call the Phosphine Awareness Team Member in tbeir state.

The continued effectiveness of phosphine is essential for growers to meet market demands for high-quality grain, free of insect infestation. Through the GRDC, farmers support several research and extension projects aimed at maintaining and improving the usc of phosphine. These include nationally coordinated resistance monitoring and management projects carried out in each of the three regions, development of rapid molecularbased tests and studies into the practical efficacy of onfarm fumigations.

Program 3 Contact: Mr Chris Newman. Agric WA 08 9366 2309 Dr Greg Daglish. QDPI 07 3896 9415 Dr Pat Collins, QDPI 07 3896 9433 Dr Barry Wallbank. NSW Agric 02 6938 1934

Phosphine Awareness Team Members Qld Peter Hughes 07 4688 1564 Qld Philip Burrill 07 4661 2944 Vic Peter Botta 03 5761 1647 SA Peter Fulwood 08 8568 6422 WA Chris Newman 08 9366 2309 NSW John Cameron 02 9482 4930

Region North, South, West