COOL GRAIN TO AVOID BUG PROBLEMS BY LOUISE IMPEY
APART FROM malting barley, all stored grain should be cooled to 5C by Christmas to prevent insect problems, advises CSL storage expert David Armitage.
“At 5C grain is a very stable material,” he says. “The initial temperature target of 12C should have been exceeded by now. Most stored grain will be around 10C at the moment.”
The cost of dropping it further is only a few pence a tonne, he stresses. “And it”s important because although storage insects can”t breed below 12C, they can still survive. “
At 5C, they reach a state called chill coma and can no longer move about or feed. They dehydrate and die.”
But that target does not apply to malting barley, which should be held at 10C to avoid germination problems, he notes.
Infestations may not appear until early spring, as the bulk surface warms and surviving insects become active. “It takes several months to turn over a generation once grain has been cooled to 15C. So if you miss the first generation, there is often an explosion in beetle numbers later on.”
Low numbers are easy to miss, which is why growers should employ PC traps and monitor them regularly, he advises.
“They are used in pairs, at the grain surface and 5-10cm below, and should be checked weekly.” But a couple of beetles in the traps do not necessarily indicate a big problem, he notes.
“It could be a local hotspot. Check again the following week to see if numbers are going up. Keep cooling to stop any reproduction.”
The very wet 2004 harvest could lead to mite trouble this winter, warns the CSL’ s Dean Cook.
“Grain came in very wet and there was tremendous demand on drying capacity. Inevitably, there were backlogs of damp grain.”
The immediate target of 18% moisture should have been replaced by now, he advises.
“With mites, moisture is the key. At a relative humidity below 65%, mites can”t breed. Below 60%, they die.”
These figures translate to moistures of 14.5% for cereals and 7.5% for oilseed rape. “But even better are 14% and 7%.” Grain surfaces which absorb moisture from the atmosphere are at greatest risk, says Mr Cook.
“Conditions there can be just right for mites. Consider a diatomaceous earth surface treatment, but always check acceptability with your buyer first.”
Another threat from a wet harvest is mould which produces the mycotoxin, ochratoxin A.
EU limits are 5ppb for grain and 3ppb for cereal products. Laboratories, including CSL, can check for mycotoxin, he notes.
“If speed of drying was an issue and some mould developed, it may be worth getting the test done.”