Temperature – more important than moisture?

Pest control expert and Dealey managing director Martin Cobbald says when it comes to insect pests, temperature is key.

I am going to say something controversial here. Moisture does not matter. I know this will sound plain strange to an industry that harvests, dries, stores and sells under a moisture target – but please bear with me.

High haulage prices mean rejection from insects can quickly wipe out your profit margin. If a load is sent back, you pay haulage to the weighbridge, haulage back to your farm and haulage to the weighbridge again. When it comes to insects getting into your grain, the overwhelming majority of rejections at weighbridge are not for moisture-loving insects, but for those that thrive in hot conditions.

We must distinguish between primary and secondary insect pests here. Primaries feed on the grain itself (e.g. grain weevil, sawtooth grain beetle, rust-red grain beetle and flour beetle). Secondaries feed on things in a grain store (e.g. hairy fungus beetle, psocids and foreign grain beetle). For the most part, these are fungal feeders so moisture plays a role in secondary insect infestation, but these insects are far rarer than those named above.

Mostly, if a load is rejected for a secondary insect it is because they have hopped on the back of mouldy conditions created by primary insects.

All primary infesting beetles except for the grain weevil are not native to the UK. If you cool your grain to temperatures they would not encounter in their country of origin, you severely debilitate their ability to breed at high rates.

Global data on insect breeding shows the average minimum breeding temperature for primary insects: If you get your grain below that temperature, you are creating a hostile environment.

Primary grain pest Base development temperature (°C)
Sawtooth grain beetle 14.34
Rust red grain beetle 16.28
Flour beetle 16.82

So, get those fans running! For those who may ask: ‘What if it’s warm outside?’, ‘What if it’s raining?’, I refer to the Home-Grown Cereals Authority (HGCA) Good Storage Guide, which states that for grain to become damp from blowing, you need a combination of:

  • Excessive aeration rates
  • Condensation around ducts in spring
  • Rain driven into uncovered external fans
  • Successive days of condensing fog.

Rain will not make a difference unless it is actively sucked into the fans that are blowing. HGCA recommends that any time the grain temperature is 4°C higher than the air temperature outside, you should be blowing. I would conclude that fans should be turned any time it is cold outside, and temperature is more important than moisture when it comes to avoiding insect pests.

Visit the Dealey website HERE.


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