18 September 1998

Cool wind chills out pests

Last year severe infestations

of insect pests in stored

grain caused huge cash

losses. This year the threat

of damage and contamination

should be less.

Edward Long reports

PEST pressure on grain coming into store was less this harvest and, given careful management, problems should be far rarer than last year.

Although grain should already have been ventilated, it is not too late to start blowing it to minimise the risk of future trouble, says Cambridgeshire-based pest control specialist Chris Stapleton of ARRESTaPEST of Great Gidding near Huntingdon.

He was kept busy last autumn and winter providing a "fire-brigade" service fumigating infested stores. "The huge build-up of insects wrecked grain quality and some cereal growers suffered the worst cash losses for many years," points out Mr Stapleton who, with son Ian, looks after grain stores in four counties.

"As the post-harvest weather was warm and humid farmers were reluctant to switch on fans, when they did start blowing it was too late as problems were already developing. Grain had settled and become compacted so it was more difficult to blow air through, early ventilation keeps it loose so air can freely circulate."

A wide range of insects can infest grain – last year there were more rust red grain beetles than for almost a decade. The father and son team was called in as early as October to fumigate stores. Normally this job does not start until late November or December. The two were flat out until March trying to retrieve the situation in infested stores.

That is why cereal growers who have not already started ventilating are urged to start the fans as soon as conditions allow. Grain will have come in off the combine at 19ºC (74ºF) or more, unless this is reduced quickly hot spots can form which provide the ideal 30ºC (86ºF) plus environment for insects.

Although grain coming into store this harvest was generally dry and in good condition, there is still a risk of trouble as many stores held old season grain right up until the last minute. There was little time for effective cleaning.

Even if stores were super-clean, insects could still have arrived in dirty trailers or emerged from contaminated augers and elevators.

Hot spots can form where a wet load has been delivered or where there is a concentration of chaff or trash to upset the flow of air through the heap. Usually the first insects to exploit them are the foreign and red rust grain beetles. But usually close on their heels comes the saw-toothed grain beetle.

Once beetles become established they cause damage by direct feeding on grain, triggering mould formation, and they can create the moist environment which spoils grain quality. Grain weevils tend to cause more direct feeding damage than beetles, they bore into the corn and larvae grow within it, feeding from the inside out.

Another pest which is gaining in importance is the grain mite. The tiny creature, it is less than 1mm long, congregates in the top 30cm (12in) of a heap where there is insufficient airflow to prevent stagnant moist air from lingering. Although mite infestation does not cause the extreme damage done by beetles and weevils, it does create a musty smell to taint grain. It is becoming more difficult to control as it is developing resistance to organophosphorus insecticides.

Often in the past the first sign of insect infestation in stored grain came when stores were opened and the first loads were rejected due to contamination or spoilage. But with increased store monitoring under the ACCS scheme the Stapletons are on stand-by this autumn as they expect to be called in earlier to nip trouble in the bud.

Although some stores are monitored by sophisticated computer equipment, a simple hand-held temperature probe is just as efficient if used properly. The ArrestApest team checks at various depths as it is easy to push down through a hot spot so miss a temperature abnormality. The temperature should be down to 14ºC (54ºF) by September/October and at its holding level of 10ºC (46ºF) or less by Christmas.

UKASTA advises stores should be checked weekly during the initial shake-down phase, then once a fortnight after the final storage level has been reached. The team is on the look-out for areas of the store which are out of step with the rest. If there is an increase of temperature but no insects are found a portable corkscrew blower is used to attack the spot before an infestation develops. &#42

GRAIN PESTS

&#8226 Ventilate stores now, if not already started and conditions allow.

&#8226 Monitor grain weekly during temperature stabilisation phase.

&#8226 Check every two weeks after final storage temp reached.

&#8226 At 5íC grain mite takes five months to complete life cycle, at 20íC, it takes 14 days.

POPULATION EXPLOSION

In three months at 30íC:

&#8226 A female saw-toothed grain beetle can produce over 1 million progeny.

&#8226 A single adult female grain mite can produce over 4m progeny.

&#8226 A single female grain weevil can produce 50,000 adults.