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Weed control: a pre-emptive strike on aphids

The first line of defence against aphids is to remove weeds in and around paddocks before sowing.

Green peach aphid adults and nymphs (Source: cesar)

 

As winged aphids take flight and migrate large distances with the help of thermal currents during autumn, it's tempting to think that the arrival of aphids in crops is beyond one's control.

But while we may have little control over what aphids get up to in the air, we can exert influence on what is happening on the ground, as aphids do have a second dispersal mechanism - walking. ­­­

Research has shown that walking can take wingless aphids far beyond neighbouring plants. For example, one study showed pea aphids (Acyrthosiphon pisum) can walk up to 13.5 metres within 7 hours, demonstrating walking aphids can contribute to infield dispersal.

Summer and autumn weeds and crop volunteers provide a refuge for aphids and viruses to survive between winter-cropping seasons. For example, Russian wheat aphid (Diuraphis noxia) can live on many grasses including those belonging to the Poa, Bromus, Hordeum, Lolium and Phalaris genera, providing ample over-summer alternatives to cereal crops. Likewise, green peach aphid (Myzsus persicae) is extraordinarily cosmopolitan, and its host range includes capeweed, marshmallow, wild radish, wild turnip, Lincoln weed and other cruciferous weeds. 

When autumn-sown plants emerge, aphids have the strategic advantage to move from this so-called ‘green bridge’, to establishing crops. This is one of many reasons to control weeds and crop volunteers in and around paddocks prior to sowing. It is important that there is a break of at least 2 weeks before sowing, in which there is no green material remaining to harbour pests. In practise, this means controlling weeds 4 – 6 weeks before sowing. This approach will not only control aphids but can significantly reduce the virus risk to emerging crops.

Further information on the benefits of green bridge control see the GRDC Green Bridge Fact Sheet.

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