Spring into action: the aphids are here!
Monday, September 21, 2020
Spring is here! While we welcome the better growing conditions, no-one likes the many pests and diseases the season also brings. Right now, our team of Consultants is helping growers across the country tackle aphids in melons, corn, strawberries, brassicas, greenhouse vegetables, flowers, and herbs. Read our tips on how to use IPM to control this common pest.
These sap-sucking insects can breed quickly, spoil produce through honeydew secretions, sooty mould and several species can also transmit viruses. For these reasons, many growers consider aphids to be their most unwelcome visitor.
The good news is that you can reduce aphids to minimal levels through an Integrated Pest Management (IPM) Program.
Understanding the aphid arrival
Aphids often seem to appear without warning, especially in early spring and autumn. They can overwinter on weeds, trees and crops, or survive on crops grown in greenhouses. They also have the ability to move hundreds of kilometres on trade winds across continents.
There are hundreds of aphid species in Australia, but the ones we see most among commercial crops are:
- Green Peach Aphid (Myzus persicae)
- Cotton (or melon) Aphid (Aphis gossypii)
- Potato Aphid (Macrosiphum euphorbiae)
- Glasshouse Potato Aphid (Aulacorthum solani)
- Rose Aphid (Macrosiphum rosae)
- Strawberry aphid (Chaetosiphum fragaefolii)
- Cabbage aphid (Brevicoryne brassicae)
Aphids react to the colour of plants. A greenish yellow colour is particularly attractive. The colour of the leaves gives the aphid information about the age and the quality of the leaf. Younger leaves are preferred as a food source and have the softest foliage and highest sapflow.
“Many agronomists have drawn a link between over-fertilisation (especially nitrogen) and aphid outbreaks,” says Stephanus Malherbe, Biological Services’ IPM Consultant and Team Leader in South Australia. “In late winter and early spring some growers apply excessive nitrogen fertilizers, hoping to get their seedlings to grow faster due to the prevailing cold conditions. The benefit of this action is limited, and it only sets the scene for increased aphid activity.”
Above: Aphid reproducing live young which immediately start feeding on crops.
Using IPM to control aphids
Aphids can be controlled with a multidimensional battle plan that begins before the pest appears in your crop.
- Start by searching nearby weeds. Aphids can survive on a wide range of weeds and can often be spotted there long before they reach your produce.
- Effective weed control is therefore the first step in limiting aphid activity on your farm.
- Properly screen greenhouse structures to stop migration from outside.
- Control ants. Ants like the honeydew the aphids produce. They help the aphid colonies grow by protecting them from natural enemies.
- Avoid over-fertilisation, particularly the excessive use of nitrogen.
- Release the appropriate aphid parasites preventatively and monitor their establishment. Increase release rates when aphids are already present.
- Use chemicals only if necessary and choose a product that doesn’t harm the beneficials.
Controlling aphids in your crop
It is important to use a range of controls in an IPM program. This helps reduce the risk of aphids developing resistance to chemicals which can happen with overuse.
“We have seen new chemical options emerge in recent years for the control of aphids. However, the ability of aphids to multiply rapidly means chemical resistance can also develop quickly. Some of the widely used aphicides in Australia are already showing signs of reduced effectiveness and this is where biological controls come into their own,” said Stephanus.
Biological Services offers four parasitic wasps – Aphidius colemani, Aphelinus abdominalis, Aphidius ervi, and Diaeretiella rapae. They can be used individually or together in an easy to release mixture. These wasps are versatile due to their wide aphid host range and are particularly effective in the mild conditions of spring and autumn.
The parasites work by depositing an egg into the aphid in a matter of seconds. The eggs hatch in a day or two and the larva begins feeding inside the aphid, eventually killing it and forming a pupae, or ‘mummy’. A new wasp emerges from the mummy to deposit eggs in other live aphids nearby. Each Aphidius female for example can parasitise over 300 aphids in her lifetime.
“We’ve already noticed the good work of Aphidius colemani in the crops we are monitoring with growers in the season to date,” says Stephanus. “It is very encouraging to see the gold-coloured mummified aphids on weeds in new greenhouse crops."
Left: Aphidius colemani mummies are a gold / bronze colour. Right: Aphidius colemani lays eggs inside an aphid.
Left: Aphelinus mummies are black. Right: Aphelinus lays eggs inside an aphid.
Aphidius colemani and A. ervi are sensitive to extreme heat conditions, but A. abdominalis can tolerate high temperatures and fill the gap.
“Naturally occurring beneficials such as hoverflies, ladybirds and lacewings are also useful. However these predators have longer life cycles and often do not build into larger populations until the aphids have been established for quite a while,” he said.
Nevertheless, aphid populations multiply quickly during the hot summer days and the timely application of compatible aphicides is required from time to time to prevent crop damage.
“We take pride in offering growers the highest quality beneficials that arrive in good condition. Importantly, our expert team of trained entomologists, horticulturalists and agricultural scientists are always on hand to tailor an IPM program for each site and help monitor crops for pests year-round.
To learn more about controlling aphids or other pests in your crops, contact your local Biological Services Consultant or our office on 08 8584 6977 or email@example.com
Did you know? The lifecycle of aphids is complicated. Adults can be either winged or wingless, depending on the circumstances. For much of the season, an aphid population consists of females which produce live young which immediately start feeding on plant sap. They grow quickly and moult four times before they become adult. Their characteristic white cast skins and signs of honeydew often betray their presence. Winged aphids generally occur where there is overcrowding, stress, or when there is a change of host plant. They can then move to other plants and cross large distances on trade winds. Aphids can therefore react quickly and effectively to changes in their surroundings. Early detection and ongoing monitoring is key.