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Granary Weevils in the Hen's Grain
How to get rid of weevils infesting your feedstock
FR: Charançons dans graine d’alimentation - poules
FR: Commment se debarraser des charançons envahisant vos stockes de grains
Weevils - easily recognised by their ‘snout’
FR: charançons - faciles à reconnaitre grace a leur ‘trompe’
This saga begins 25/08/2023 when I travelled more than one and a half hours NW into the Gers dept, SW France, in order to purchase grain for my flock of 50 hens. The farmer poised my 600kg bigbag order onto the trailer, I paid my dues, and he disappeared into his house.
As was my habit, I unloaded 100kg to reduce weight on the trailer axle; four sacks going into the car. This was done with a bucket and large paper sacks, giving ample opportunity to scrutinise the product. In so doing I inevitably noticed the presence of weevils. I was stuck between judging their presence to be ‘just a few’ or ‘an infestation’ - and realised that I should alert the farmer to discuss or argue the matter. But what-if ??? I was blocked from making a right decision and set off on the return journey. I was reluctant to think this grain could be wasted - and hens gobble up insects anyway, right ? Well, this logic could cover immediate consumption, but 600kg of grain could last several months - time enough for the multiplying pests to convert carbs into frass.
Twenty minutes later I decided the least I should do was to alert the farmer to my concerns, so I texted him to this affect. Then with plenty of journey time for reflection I worked out how I might treat the grain to eliminate the weevils. All living creatures need oxygen and expel carbon dioxide, so if deprived of oxygen ? It seemed logical, a bit of research and practical DIY could resolve the matter.
That evening I called up the farmer who expressed surprise at the state of the grain, and promised his support in compensating my time and losses made in finding a remedy.
Weevils are hardy creatures tolerating a range of temperatures but can be killed by extremes of temperature. They might also die with prolonged deprivation of foodstuff, but ‘mine’ had more than enough to complete several laps of life-cycle before going into the red ! They can also be treated with fumigation, of which several noxious chemicals were proposed, and discounted; my hens feed exclusively on organic certified grain and all chemicals are taboo.
The option to treat by deep freezing or over-temperature ( > 50 degC ) could be practical for smaller quantities, but the sheer bulk of my 500kg ( after taking out 100kg for immediate use ) was out of question for my diminutive freezer ( nearly full already ) or otherwise the overheating option - in which the batch would need splitting into many small sacks to ensure heat penetration. The choice came back to fumigation by CO2, with the promise of holding zero side effects. Key reference
It took me a couple of weeks to track down a CO2 bottled gas supplier in my local town - not commonly available in the supermarkets. Rather, from a wholesale professional catering supplier. Initial impression was costly: 40 euros for 10kg gas content, 80 euros for the robust 18kg bottle - as refundable deposit. The cost was soon dispelled upon reflection - value of the grain was 280 euros, so even if it took all of the bottle contents, the treatment could pay for itself.
As used to pressurise the beer pumps !
FR: Comme utilisé pour mettre la biére sous pression
Next was to fix on and pursue the method: transfer all the grain from the trailer bigbag into a second bigbag - sitting independently on a palette, plus a sheet of heavy duty polythene - Visqueen - the variety used to cover a polytunnel. In order to facilitate gaseous penetration, a netted wire frame cage would be placed centrally in the grain.
Unloading the grain from trailer bigbag to a 2nd static bigbag set up on a palette
FR: Decharge de grains de le bigbag sur la remorque - vers la 2eme bigbag posé sur palette
The grain displacement proved to be a major disruption for the weevils - which climbed the bigbag walls - in an escape bid ? Well, one may imagine just how torn would be the decision to set off into the unknown - and quit such a vast resource ;)
Loading complete; at centre is a the netted cage. NB. escaping weevils !
FR: Chargement complet; au centre la cage recouvert-filet. NB. les charançons echappent !
On reaching the bottom of the bigbag I found a big clue as to weevil presence - a damp caked layer of rotting grain. This bigbag had either been later refilled on top of older grain, or rather, been filled and stocked off a palette, where moisture ingress had taken place from the ground up. Grain with higher moisture content is more attractive to weevils - and perhaps essential for completing their life cycle of consuming, boring and pupal development.
Last layer at bottom of the trailer bigbag - damp & mouldy clumps of rotted grain
FR: Derniere couche au fond de la bigbag - mottes de graine humide et moisi
Once the grain was installed into the new static bigbag, next step was to seal up the whole perimeter with professional sticky tape. Fortunately we had a reel of this - as used to improve air sealing in new housing construction. Beware - very sticky ! It proved easier to pin the tape sticky side up onto a board, then match plastic border into place. I did also use a couple of batten wood clamps to secure folded borders.
The gas outlet on the bottle was puzzling - approx 22mm threaded pipe, a non standard to the water-plumbing domain, and a quick look at butane gas pipe fixings also foiled purpose. Time enough spent - I would make use of an old bike inner tube, fixed simply with a circlip. The tube would descend into the netted cage - thus flushing air outwards when the CO2 was injected.
The operation began officially 17/09/2023 and completed 18/10/2023 . The long cycle time is essential ( and may be regarded as a minimum ) because we are not just out to kill living adult weevils, but also emergent new weevils at completion of pupal development. The life-cycle duration will depend on seasonal temperatures, which in full summer will move along at a swift pace.
The polythene is sealed into a ‘gas tight’ envelope enclosing the bigbag
FR: La polythene est fermé pour faire une envelope ‘etanche’ autour la bigbag
In fact my gas tight envelope was quite leaky. I had estimated the need for just 2kg of CO2 to surround and attain majority proportion in the envelope. The once bulging envelope lost it’s distension after 2-3 days, so I resigned myself to topping up at intervals. At least the majority presence of the CO2 was guaranteed after several top-ups. At finish of the treatment I had used up 8kg of the contents.
Food grade carbon dioxide is released into the envelope via a tube
FR: Dioxide de carbone - qualité alimentation - laché dans l’envelope a travers un tuyau
Condensation is a problem inside a polythene envelope ! Daily temperatures push humidity into the surrounding gas, night time external temperatures force this humidity to condense on the inside of the envelope. I placed a crate on top of the filled bigbag such that this humidity would not directly contact the grain. In this fashion condensation will return into the gas as external temperatures re-heat. Some of the moisture ran and collected in folds at a level below the pallette base.
After 31 days treatment; a better view of the netted cage with tube in situ
FR: Apres 31 jours traitement; un meilleur regard sur la cage avec entourage filet
So was the experiment a success ? Largely. I took samples from the grain at various levels / stages of unloading, to check for weevils. Zero living, quite a few dead. The presence of live moving weevils is easy to detect , not so those which are immobile, dead. It seems 99% sure that all adult weevils were killed in this treatment. What is not so evident is the destruction of unhatched weevils - which may yet have not completed incubation; so I may yet have a different answer to post in the months to come, but with winter temperatures slowing down all insect life, I am optimistic that the hoped for objective is fulfilled.
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