Latest Aphid Report

Updated Jul 5, 2024

Mid Canterbury has followed South Canterbury and Southland in recording dramatic drops in winged aphid numbers caught on sticky traps. Some growers hosting monitor paddocks chose to apply foliar insecticide in the last couple of weeks; this appeared to be well justified in most cases. For now, though, the risk period seems to be over, and the low level of aphid pressure would be expected to remain until spring.

What Is The Risk To My Crop?

Data represents the average number of winged aphids captured per sticky trap over the monitoring period, as well as the number of beneficial insects. In order to mitigate risk, all aphids identified in this programme are assumed to be cereal aphids. Beneficial numbers, while useful as a guide, can vary hugely from farm to farm and paddock to paddock, as they are influenced by such factors as insecticide history, surrounding habitats such as native plantings, and microclimates.

What Are My Risk Considerations?

See All Weather Data

Forecast data should be considered when making decisions around foliar insecticides. If cold, wet weather is forecast, aphid numbers will fall naturally and an insecticide may not be needed. Take into account the number of aphids present and the amount of beneficial species as well.

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Aphid Numbers

When numbers of winged aphids are high, there is an elevated risk of primary infection by YDV, as well as spread within the crop. In particular, look for a recent increase in aphid numbers that could indicate the onset of a risk period. Look for wingless aphids in the crop on warm, dry days.

Natural Predators

Aphid numbers can be controlled naturally by allowing the numbers of beneficial insects (e.g. ladybirds and parasitic wasps) to increase. While natural predator numbers tend to lag behind aphid numbers by a few weeks, a consistent increase in aphid numbers without significant beneficials can indicate that a foliar insecticide could be warranted.

Cultural Control

Be aware of areas surrounding your paddocks that may act as alternative hosts for aphids such as trees and hedges. Sowing into good, weed-free soil also removes alternative hosts where aphid infestations could originate.

Chemical Spray

If all other factors point to an increased risk period for YDV infection, consider using a foliar insecticide. Not all aphicides are created equal; some are also lethal to beneficial insects, which could lead to a greater problem down the road.

Why Monitor?

YDV transmitted by aphids is an economically important virus in New Zealand cereals, causing up to 30% yield loss in some years. There are a number of ways to prevent yield loss due to YDV; most aim to reduce the risk of aphid colonisation and spread, and often rely on the use of seed treatment and foliar insecticides. As a result, cereal growers can spend around $100/ha, annually, controlling aphids to prevent the spread of the virus. However, alternative approaches, such as Integrated Pest Management (IPM), which combines the use of natural predators and parasitoids with cultural controls and selective chemistry as required, are available. Making use of regional data or, even better, monitoring your own crops, can save time and money by letting you only apply insecticide when it is needed.

Monitoring and Identification

Insect identification can be challenging, but with a bit of practice and a magnifying glass, growers and industry reps can determine friend from foe. FAR is here to support growers interested in learning more about monitoring, and offers field walks, workshops or help with sticky trap or insect photo identification. Use the provided links for further information.

 

What Are Beneficials?

Let the good guys do the work!

A wide variety of beneficial predators and parasites contribute to pest control in arable cropping systems. Some are resident predators that live in the crop all year and play an important role in helping to control establishment pests (pests that inflict the most damage while the crop is getting established). Others are transient and only arrive in a crop if there is a pest present to eat.

Predators (such as brown lacewings) are relatively large (adults 9-10mm) and eggs are white and fairly obvious on a green leaf.  So predators are quite obvious and their impact is immediate as they kill and eat their prey.  However, parasitoids (insects that parasitise other insects)are more difficult to see as they live most of their lives hidden inside the bodies of the hosts. The easiest stage to see is the pupal stage when the wasp takes over the body of the host aphid and puffs it up to make its own cocoon (a "mummy").  Adult wasps that parasitise aphids are small and active but can be caught on sticky traps.  

When broad spectrum chemicals are withdrawn from a farming operation, it may take a while for the resident beneficial populations to build up enough to contribute to pest control, whereas transient beneficial insects may fly into a paddock and maintain a presence if no broad-spectrum chemicals are being used. IPM aims to increase populations of resident beneficial species and make the best use of transient beneficial species.

Aphids and YDV

Aphids can be born either with or without wings. Winged aphids may be present throughout the year, but mostly in the warmer months. These winged (alate) aphids are responsible for primary infection of YDV when they fly into the crop carrying the virus within their bodies and begin feeding on the sap of the crop. Secondary infection occurs when aphids reproduce asexually within the crop, giving birth to live (usually wingless) young. Aphids can also reproduce sexually, laying eggs which can overwinter in the paddock or in nearby plants (weeds, hedges, trees, etc.).

Growth Stages

Cereal crops are most susceptible to yield losses caused by aphid-vectored viruses before Growth Stage (GS) 32. Insecticide-coated seed generally confers protection to autumn-sown crops until GS21 (tillering). FAR's guide to determining cereal growth stages is provided in the link.

Insecticide Considerations

  • Check the product label
  • Take growth stage into account
  • Consider impact on beneficials
  • Have you just used a broad spectrum insecticide?
  • Will there be time for beneficials to build up again or is there already a healthy population?
  • Seed dressings may provide initial cover
  • What are your MRLs?
  • Your risk period will be different after spraying
  • You may need to go and do monitoring after spraying, too.
  • Consider calibration of spray gear
  • Worker health and chemical toxicity
  • There may be more options available

Insecticide Options

Products Last Reviewed Mar 21, 2024
Tau-fluvalinate
MAVRIK

Mode of Action: Synthetic pyrethroid. Acts primarily as a contact poison by interfering with the central and peripheral nervous system.

IRAC Group: 3A

Beneficial Impact: SAFE FOR WASPS

lambda-cyhalothrin
KARATE ZEON, CYHELLA, HALEX CS, LAVRON, TAEKWANDO 250 CS

Mode of Action: Synthetic pyrethroid. Primarily a contact and stomach poison with direct effects on the nervous system of susceptible insect pests.

IRAC Group: 3A

Beneficial Impact: HIGH

sulfoxaflor (Isoclast™ active)
TRANSFORM

Mode of Action: Sulfoxamine

IRAC Group: 4C

Beneficial Impact: Medium

Pirimicarb
APHIDEX, PIRIMOR, PIRITEK, PROHIVE

Mode of Action: Carbamate. A fast-acting contact insecticide which is partially systemic and has strong fumigant action within the crop.

IRAC Group: 1A

Beneficial Impact: Low. Will affect some parasitic wasps if they are directly sprayed.

Chlorpyrifos
Multiple generics

Mode of Action: Organophosphate. Has contact and vapour action and also acts as a stomach poison when ingested. Acts directly on the nervous system of susceptible pests.

IRAC Group: 1B

Beneficial Impact: High impact on all insects, including beneficials.

Contact FAR Aphid Specialists