BEATING RISING PHOSPHINE RESISTANCE
The first phosphine resistant species detected in grain stores in NSW was found in 2007, and the last decade in farming across Australia has seen a dramatic rise in phosphine resistance pest species.
With markets expecting high-quality grain that shows no signs of pest infestation, growers have turned to a heavy, often misuse of phosphine, to ensure the highest quality, pest-free grain.
This reliance, however, seems to be what is leading to phosphine resistance in pest species; predominantly lesser grain borer, rusty grain beetle, rust red flour beetle, rice weevil and saw-toothed grain beetle.
There are several reasons for the rise in phosphine resistance in grain stores, detailed below:
1. Fumigating unsealed stores:
The main reason for the sharp rise in the number of phosphine resistant species seems to be the increased use of fumigation in unsealed stores.
We have quite often spoken about fumigation and sealing silos, and we’re going to reiterate some of that information here.
To be effective against grain pests at all stages of the life cycle, gas fumigation needs to be dispersed at a certain level of concentration.
As phosphine is a mobile gas - meaning it moves around in the store - grain silos which are not gas tight or that have leaks will lose phosphine, making the fumigation weaker and less effective.
This leads on to the second point.
2. Multiple poor fumigation attempts:
If your first fumigation attempt in an unsealed silo didn’t do the job 100%, you’ll likely want to try it again.
However, repeated unsuccessful attempts at grain store fumigation is simply giving the grain pests more opportunity to build up resistance against phosphine; potentially growing more resistant with every failed attempt.
3. Incomplete cleaning of grain stores:
Poor hygiene inside your silos can also lead to resistant insect populations in your grain stores.
When cleaning out your silo between storing grain varieties, it is imperative that the silo is completely cleared, leaving no residue in hard to reach areas where pests can hide.
The best way to clean your grain silos is the following:
After the sweep has done two laps, shovel and sweep the grain into the auger sumps while the auger is off.
Empty the auger when out of the silo.
If you’re concerned about any residual grain in the auger pipe, air can be blown down the auger.
Additionally, a washdown will remove grain and dust left in any crevices and harder-to-reach place. Cleaning and washing on a warm, dry day will help the grain silo dry quickly to avoid rust.