Warning on pests with summer crops

23 Feb, 2001 10:00 PM
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WHERE there's an upside, always look for the downside.

That's the case with the surge towards summer cropping and the loads of upside in terms of water use, summer grazing benefit and silage.

But two AgWA researchers warned delegates at last week's Crop Care Updates conference

According to Debbie Thackray, the anticipated increase in warm season (summer) cropping and lucerne plantings will increase the survival rates between winter growing seasons for some pests and diseases, which previously persisted over summer only on weeds and crop volunteers.

This is because some viral and fungal diseases of broadacre crops can only survive from the end of one winter growing season to the start of the next on green plant material -- the so-called "green bridge".

Roger Jones said that the likely consequence of having perennial pastures in the wheatbelt was a substantial build-up of legume pests and diseases that were unable to persist over summer in dormant seed in the soil.

An additional problem was that lucerne sowings in WA were being done with untested seed, most of which came from the eastern states.

These lucerne seed stocks were harvested from plantings in regions where a number of seed-borne diseases occur.

This could results in epidemics of alfalfa mosaic virus, which also affected nearby pulse crops, especially chickpeas and faba beans and luteovirus, which affected legumes.

According to Ms Thackray, early control of weeds and crop volunteers to create a fallow before sowing can greatly reduce disease and insect pressure on emerging crops.

For many pest and disease problems, the greatest damage is done when they occur early in the life of the crop.

"Also consider the risk associated with planting infected seed," she said.

"For example, if aphids are expected to arrive early following a wet summer, then CMV-infected lupin seed should not be sown.

"Use predictions based on summer rainfall as to if and when to apply insecticides.

"This is especially useful when it is hard to find aphids and virus symptoms in crops, as considerable virus spread can occur with low aphid numbers and before symptoms can be seen."

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