Early Season Crop Aphids

April showers not only bring May flowers, but also some uninvited guests—aphids. These pests are making themselves known, with reports coming in from the Northern Country in Victoria, and the North West and Central West regions of New South Wales.

What’s the situation?

April brought much needed rain for eastern areas and the Riverina district of NSW, as well as to central, north central, and southern Victoria.

After above-average rainfall in March and April, aphids tend to infest crops early in season, whilst moisture stressed cereal crops are more vulnerable to damage.

Identification of common aphid species affecting broadacre crops.

To start, knowing what aphid is causing problems is a cornerstone for effective pest management.

Different aphid species have their preferred host plants, making it easier to identify potential culprits based on your crop type.

If you’re growing cereal crops, watch out for the Russian wheat aphid and oat aphid – they’re the usual suspects this season. In your canola fields, the green peach aphid takes center stage. For those growing pulses, it’s the cowpea aphid that’s your biggest concern.

Of course, these aren’t the only aphids you might encounter. To help you stay ahead, we’ve compiled a guide to common aphid pests in major winter crops to help you narrow down your likely encounters.

Need more info?

For detailed information on aphids, visit their profile on our pestnotes resource.

And if you ever find yourself scratching your head trying to identify these pests, download Crop Aphids: The Back Pocket Guide or simply reach out to us for a helping hand.

How crop infestations start

Aphids are present year-round, surviving between growing seasons on volunteer crops, weeds and irrigated crops in the summer and early autumn.

Winged aphids migrating from these plant hosts, known as ‘green bridges’, introduce aphids into crop environments, which then give rise to colonies mostly consisting of wingless aphids.

With asexual reproduction and favourable autumn temperatures, rapid population growth occurs. Aphids arriving in crops during autumn that persist over winter may lead to large, damaging populations that peak in late winter and early spring.

Impact of aphids on crop yield and quality.

Aphid infestations aren’t just a nuisance; they’re a significant issue for crop productivity.

These sap-sucking pests remove nutrients: stunting growth, causing early leaf senescence, and reduce tillering in young plants.

As populations grow the problems escalate, including deformed leaves, wilting, yellowing, leaf curling and leaf drop, and reduced dry matter production.

Aphids worsen their impact by secreting honeydew, fostering fungal growth that further hampers photosynthesis and plant growth.

Some aphids also cause distinctive damage, such as Russian wheat aphids, which result in longitudinally rolled leaves and chlorotic streaking, and cowpea aphids, which can cause skin and eye inflammation in livestock grazing on infected pastures.

Russian wheat aphid and chlorotic streaking on wheat, Photo by Elia Pirtle

Viruses

Many aphid species also are known virus vectors, spreading viruses between plants as they feed.

The capacity to transmit viruses varies among aphid species. For instance, oat aphids are known to transmit several significant plant diseases, including barley yellow dwarf virus (BYDV).

Similarly, the green peach aphid serves as a key vector for turnip yellows virus (TuYV, formerly known as beet western yellows virus) and other plant viruses.

Virus infections are more prevalent in high rainfall cropping zones, particularly where green bridges serve as reservoirs for virus and aphid populations during the early growth stages of new season crops. Yield losses are higher in crops infected at the vulnerable seedling stage.

Control considerations

Before resorting to pesticides, take a moment to consider a few important factors.

Firstly, evaluate if chemical control is necessary by using economic thresholds or ‘rule of thumb’ guides where available, which can be found in our PestNote series.

Even if thresholds suggest action, assess current growing conditions and moisture availability. Healthy crops can often rebound from damage and tolerate higher aphid levels than moisture-stressed plants before experiencing significant yield loss.

Also consider that different aphids have different habits, so tailor your spraying approach accordingly. For example, aphids like the Russian wheat aphid, which cause leaf rolling or have cryptic feeding habits, require thorough coverage and the use of insecticides with fumigant or systemic activity.

Consider resistance management, as some aphid pests, such green peach aphid and bluegreen aphid, have evolved resistance to commonly used chemicals. Reserve insecticides as a last resort for high-risk situations where other methods have failed, and rotate between insecticides with different modes of action to minimize the risk of resistance.

Seed Treatments

Insecticide seed treatments are your first line of defense against aphids, offering protection during the crucial establishment stage for up to five weeks or even longer. These treatments often reduce the need for foliar insecticide sprays in autumn and winter.

There are various seed treatments available, each offering different levels of efficacy and duration of protection. Local environmental conditions can also influence their performance.

However, be aware that resistance in the green peach aphid can significantly diminish the effectiveness of neonicotinoid-based treatments. So, even if you’re using seed treatments, it’s essential to monitor your emerging crops for early signs of aphid activity.

Aphid Action Plan: Our Advice

As always, we suggest Integrated Pest Management (IPM) Strategies be employed to give your crop the best chance at protection.

  1. Weed Out Trouble: Manage summer and autumn weeds to reduce alternate hosts between growing seasons. If possible, coordinate with neighbours for an area-wide approach.
  2. Vigilance Pays Off: Regularly monitor for aphids from sowing through stem-elongation at 3-5 locations in the crop, examining 5 plants at each location.
  3. Stubble Savvy: Whenever possible, sow into standing stubble to reduce the risk of aphid infestation, as young seedlings are most easily identified by flying aphids if against a background of bare earth.
  4. Keep your friends close: Keep an eye out for beneficial predators, parasitoids, and aphid mummies. Utilize resources like AgPest to help identify them.
  5. Spray smart: When warranted, consider the targeted use of selective insecticides. Broad-spectrum chemicals might seem like a quick fix, but they’ll also take out your beneficials in the crossfire. Consult the beneficials chemical toxicity table to ensure you’re not inadvertently putting your allies at risk.

Acknowledgements:

Thank you to Zorica Duric, Benjamin Romeo and Joop van Leur for reports, and to Paul Umina for reviewing and contributing to this article.

Cover image: Cowpea aphid, by Andrew Weeks Cesar Australia

What is Pestfacts south-eastern?

PestFacts south-eastern keeps growers and advisers informed about invertebrate pests and beneficials in broadacre crops and pastures during the winter-cropping season in Victoria and southern New South Wales.

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