Jack and John Elliott ponder the condition of their Cowrie and Asgrown 6785 soybeans after electrical storms with rain squals delivered 175 millimetres over four days. They were ready to spray with Steward when the rain came. Unfortunately many plants had their main growing points eaten by grubs (tipping-out).

For 25 years canegrower John Elliott has been growing soybeans at Empire Vale south of Ballina.

Three years ago John’s soybean crop was given a touch-up by silverleaf whitefly.

In retrospect he admits that a mistake was made by spraying Lannate (methomyl) early and once again at flowering.

'These sprays caused silverleaf whitefly to flare-up and pockets of sooty mould to develop within the crop - as a consequence we lost 30 per cent of our expected crop yield,' he said.

After listening to a talk by Hugh Briar, a respected Northern Australia pulse entomologist, based with Queensland DPI at Kingaroy, John decided to adopt Hugh’s integrated pest management ideas.

'It was the time to take a stand and reduce the number of hard sprays,' John declared.

Last year John applied only one Dipel (Bt) spray at flowering. His soybean yield was good but some grain suffered slight wrinkling of the seed coat due to rain.

Pesticides commonly used for conserving beneficials in soybean crops include: Bt(k) products, nuclear polyhedrosis virus products, indoxycarb and spinosad products.

John advises growers using the virus and Bt sprays not to let grubs get too large. Another observation by John is, once it was easy to kill all grub sizes with Lannate (A carbamate) but 'today you must target small grubs and use the high rate'.

John’s experience is consistent with heliothis developing resistance to carbamates in cotton growing areas.

NSW canegrowers have adopted regular monitoring of soybean crops for insect pests and beneficials. Most growers now use targeted and soft pesticides to conserve beneficials and lessen environmental impacts.

Just recently, John and his father Jack have noticed that hares have taken a liking for the soybeans.

'We have been over-run with hares since they poisoned all the foxes,' said Jack.

Much the same happens when you kill all the predators and hyperparasites of silverleaf whitefly. Thanks for the allegory, Jack.

- BEDE CLARKE

This story appears in Agriculture Today.