Who do you want to feed? Evil weevils… or your animals? Ion Staunton* writes.
Insects find and eat stored grains and stockfeed… unless you use a natural pyrethrum insecticide to spoil their party like: Picket Insecticidal Concentrate… like a picket line or guard to protect your produce.
Weevils and grain borers deposit their egg in through the seed coat and the hatching larva spends its feeding life hollowing out the grain. Grain beetle adults can wiggle through the mass without brightly coloured shirts and eat and lay eggs anywhere.
Moths with wings can’t crawl through the mass so their attack is focused on the surface. If the grain/feed is in a bin or silo, the top is vulnerable. Wherever the caterpillar crawls it leaves a strand of silk behind it. This silk webbing covers the surface if it’s been under attack for a few months.
Most grain pest adults lay 200–400 more eggs and it is generally a 4–6 week life cycle. You don’t need to be a mathematician to work out: if you want to keep grain/feed/seed for say nine months there will be a lot of dust and empty grains by then… unless you treat it as it goes in.
Insecticide is usually applied as a liquid spray at the point where the grain tumbles into the silo/bin. The spray rate is one litre to a tonne of grain. This has no significance on the moisture content of the mass as one litre is equivalent to 1kg in 1000kg or 0.1%.
Not every grain is covered of course but, as the insects – whether as larvae or adults – move through the mass, they come in contact with enough residual insecticide and die before more eggs are laid.
A grain/seed that has already had an egg laid inside will still be hollowed out by the larva inside but when that larva pupates and then emerges to find a mate and begin feeding, it will be killed. The top of the bin or silo is often subject to quicker degradation especially if there is some UV light.
So-called seed dressing chemicals are specifically for protecting seed; they contain a fungicide as well as insecticidal components… but then they can’t be used for stockfeed.
Picket Insecticidal Concentrate can deliver 6–9 months of protection and yet has only a 1-day withholding period… meaning the grain can be sprayed today and from tomorrow it can start being fed out to stock… or sold for milling and human consumption.
*Ion Staunton, entomologist and owner of Pestech Australia and author of this article, is the entomologist that introduced and worked with all the state grain handling authorities back in the 1960–70s. He remembers standing beside one of the first specialised trucks delivering bulk grain to mills and hearing the dull ‘roar of a million munching weevils’ coming out through the aluminium sides. No one hears that any more. Contact: ion12@me.com or phone 0407 308867.
