When most Growers walk into their greenhouse every morning to inspect their crops, they want to see healthy plants that are consistently producing the best quality produce or flowers. But the problem is that many Growers often find something else in their crops – the disturbing presence of curling leaves, deposits of honeydew, and sooty mold – tell-tale signs of Aphid infestations!
While many Growers have encountered at least one species of aphids feeding on their plants at some point, the impact they can have on a farm’s bottom line when pressure starts to increase shouldn’t be underestimated.
If you’re a Vegetable or Soft Fruit Grower, aphid feeding damage directly impacts your yields and profitability. Their feeding damage will reduce your plants’ capacity for photosynthesis, leading to reduced growth. The honeydew deposits from their feeding damage can also result in sticky fruits, making affected produce unmarketable or requiring additional costs to wash.
If you’re an Ornamental Grower, aphid feeding damage has a similar direct impact on your farm’s profitability. Their damage can degrade the visual appeal of your plants and flowers, resulting in unmarketable losses.
We understand how frustrating it can be to sustainably keep aphid infestations under control, and prevent those costly situations from happening. You shouldn’t have to resort to overusing pesticides or going over your biocontrol budget to control this enemy, when outbreaks can be prevented.
In this blog post, we begin our deep dive into the first part of a series on Mastering Sustainable Aphid Control. There are many ways to control aphids, but developing a sustainable strategy is crucial for farms that need to increase their profitability. Throughout this series, our focus will be on presenting vital insights and tips for:
Green Peach Aphids Myzus persicae
Cotton-Melon Aphids Aphis gossypii
Potato Aphids Macrosiphum euphorbia
Foxglove Aphids Aulacorthum solani
Chrysanthemum Aphids Macrosiphoniella sanborni
The first step for creating a sustainable strategy against aphids is to know your enemy, by understanding how they can reproduce and spread in your crops, and learning key differences in the behaviour and identification of these common species.
Despite their small size, aphids have a surprisingly complex life cycle and exhibit a range of behaviours that make them particularly challenging to control. Uncovering their vulnerabilities will help you find the most cost-effective ways to prevent outbreaks.
So let’s begin!
1. How Aphid Feeding Habits Damages Crops
Aphids are soft-bodied, pear-shaped insects that range in size from about 1 to 10 millimeters. Their colour can vary widely, with species appearing green, yellow, black, brown, red, or even pink. One of the most distinctive features of aphids is the presence of two cornicles—small tube-like structures on their abdomen. These cornicles secrete a waxy substance that can deter predators. In between the cornicles, there is a structure called the cauda. This is also a useful structure for identification purposes.
Aphids feed by inserting their specialized mouthparts, called stylets, into plant tissue. These stylets are long and needle-like, allowing the aphid to reach the plant’s phloem (the plant tissue that moves sugars, proteins, and other nutrients throughout the plant), where they extract nutrient-rich sap. As they feed, aphids excrete a sugary liquid known as honeydew. This honeydew can attract ants, which in turn “farm” aphids by protecting them from natural predators. The honeydew can also encourage the growth of sooty mold, a fungus that blackens the surface of leaves and interferes with photosynthesis.
2. How Aphids Reproduce and Cause Rapid Infestations
One of the reasons aphids are such formidable pests is their incredible reproductive capacity. Most aphid species can reproduce with (sexually) or without (asexually) a mate. During the growing season, aphids primarily reproduce asexually through a process called parthenogenesis, where females give birth to live young (known as nymphs) without the need for mating. These live nymphs are also born pregnant and will be giving birth in a couple days. This allows aphid populations to explode rapidly, especially under favourable conditions.
When environmental conditions become less favourable, such as in the fall, aphids will often switch to sexual reproduction, producing eggs that can survive harsh winter conditions. These eggs will hatch in the spring, giving rise to a new generation ready to colonize plants as soon as they start growing.
3. Winged and Wingless Aphids: A Strategy for Survival
Aphids are typically wingless, which allows them to stay close to their food source. However, when populations become too large or when their host plants start to deteriorate, some of the aphids will develop wings. Stress from insecticidal sprays or drenches can also trigger the development of winged aphids. These winged aphids can then move to new plants, spreading infestations over larger areas.
4. The Major Enemies: 5 Key Aphid Species and Their Differences
Now that we have a foundational understanding of aphid biology, let’s turn our attention to the five species that pose significant challenges to many Growers. Learning how to correctly identify the species present in your crops is crucial for taking effective and economical steps to keep hotspots under control. Without proper identification, Growers can risk using inappropriate biocontrols - resulting in uncontrollable aphid numbers and costly financial consequences.
It is important to note that you should only try to identify adult, wingless aphids as the nymphal stages of many species can have a similar appearance.
4.1. Green Peach Aphids (Myzus persicae)
Host Plants
The Green Peach Aphid is one of the most widespread and polyphagous aphid species, feeding on over 400 different plant species. While it is particularly notorious in peach orchards, it also infests a wide range of vegetable and soft fruit crops, including peppers and strawberries, as well as chrysanthemums, gerberas, and many other ornamental crops.
Appearance
Green Peach Aphids are small, usually around 1.5 to 2 millimeters in length. They are typically pale green, although some individuals may be yellow, pink, or even reddish. The Green Peach Aphid has a smooth, pear-shaped body with relatively short cornicles and legs. Their cauda does not extend past their cornicles, and their antennae are the length of their body or shorter. If you look at their forehead, you will notice an indentation between their antennae. Their cornicles are the same colour as their body but may have black tips.
4.2. Melon/Cotton Aphid (Aphis gossypii)
Host Plants
The Melon Aphid, also known as the Cotton Aphid, is a highly polyphagous pest that affects a wide range of crops. It is particularly problematic in cucurbit crops like cucumbers and melons, and they can infest various ornamental plants.
Appearance
Melon/Cotton Aphids are small, measuring around 1 to 1.5 millimeters in length and have a rounded, pear-shaped body. They vary in colour from pale yellow to dark green, with some individuals appearing almost black. The key differentiation characteristic is that their cornicles are short and black.
4.3. Foxglove Aphid (Aulacorthum solani)
Host Plants
The Foxglove Aphid is highly polyphagous, meaning it feeds on a wide variety of plants. While it was originally associated with foxglove plants, it is now commonly found on a range of ornamentals, vegetables, and even some fruit crops. This species commonly infests peppers, tomatoes, and many varieties of potted and cut flowers.
Appearance
Foxglove Aphids are usually pale green or yellowish-green, with darker patches at the base of their cornicles. They have long legs and cornicles, giving them a more elongated appearance compared to other aphid species.
4.4. Potato Aphid (Macrosiphum euphorbiae)
Host Plants
As the name suggests, the potato aphid is a common pest of potato plants. However, it also infests a variety of other crops, including tomatoes, peppers, and many different ornamental crops.
Appearance
Potato Aphids are larger than many other aphid species, with adults measuring up to 5 millimeters in length. They can be either pink or green, and they have long, slender bodies with relatively long legs. Their antennae are longer than their bodies and their cauda is as long or extends past the cornicles. The cornicles are the same colour as their body but may have black tips.
4.5. Chrysanthemum Aphid (Macrosiphoniella sanborni)
Host Plants
The Chrysanthemum Aphid is a specialist species that primarily infests chrysanthemum plants. It can be found in both cultivated and wild chrysanthemum plants, and it is a significant pest in commercial chrysanthemum production.
Appearance
Chrysanthemum Aphids are a small aphid species, typically ranging from 1.5 to 2.5 millimeters in length. These aphids are usually dark brown to black in colour, with a distinctive waxy coating that gives them a somewhat shiny appearance. They have long, slender cornicles that are prominent and darker than the rest of their body, along with their antennae that are almost as long as their body.
Sustainably preventing aphid outbreaks requires a strategic approach, that begins with understanding the biology of aphids in order to predict their behaviour and uncover their vulnerabilities. We've only scratched the surface of Mastering Sustainable Aphid Control. In the next part of our series, we’ll explore practical strategies for managing each of these key species and share insights on how to optimize the performance of aphid predators and parasitoids.
Take Action!
Ready to defend your greenhouse production against aphid outbreaks? Don't wait until it's too late! Schedule a call today with our experts to receive strategic advice, tailored to your farm's specific needs. Our team will help you develop a customized strategy to prevent thrips outbreaks ecologically and economically.
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