Aphids are commonly found on plants in small numbers and may not do any noticeable damage. In a healthy organic vegetable garden, their populations will be continuously controlled by ladybugs and other predators that eat them.
Despite this, if the health of your vegetable plants declines due to drought or poor soil conditions, aphids can quickly multiply. Large numbers of aphids can directly damage plants by feeding on plant sap while inducing a range of other plant problems.
Knowing how to identify aphids and signs that there’s an aphid infestation is important for a vegetable gardener. Identifying an aphid problem early on will help you to easily get rid of the problem.
1. Small to moderate-sized (2.0 – 3.5 mm long) winged or wingless insects visible on plants
Aphids are small pear-shaped plant-sap sucking insects that are closely related to whiteflies and scale insects. They come in a range of colors, including green, black, gray, pink, or white with a fluffy coat. They are commonly known as greenflies and blackflies but color can’t be used to identify them because the same species can come in different colors.
They come in both winged and wingless forms. Winged forms usually appear when host plants are crowded and aphids need to find another source of food so must move to another plant.
2. The insects are pear-shaped with two tubular projections (cornicles) on the rear end
All aphids have two tubular projections, which are known as cornicles on their rear end. Aphids use their cornicles to secrete pheromones that defend them against predators. Cornicles can be easily identified in some species but are not easily visible in other species and winged forms.
3. The insects are clustered under leaves, on stems, and on growing tips of plants
Aphids are usually found clustered on plant parts that they are sucking sap from. Like many other pests, they like to remain under leaves for protection from predators.
4. Plant leaves are wilted and distorted; leaves and tips eventually turn yellow and fall off
Aphids pierce plant stems and veins to suck out sap from the phloem of plants. The phloem contains nutrients produced by photosynthesis in leaves. When a large number of aphids suck out the nutrients, the leaves and stems of the plant become wilted and distorted due to a lack of nutrients. Eventually, the leaves and growing tips turn yellow and fall off.
5. Honeydew (sticky sugary secretions) left on leaves
The main component in plant sap is sugars and many of the sugars are ingested by aphids and the excess is passed out. These secretions, which are commonly referred to as honeydew, are sticky and are left on leaves. Honeydew can create additional problems as we will see below.
6. White cast skins left on leaves
Aphids have complex life cycles, which can differ slightly between different species of aphids. In general, once the eggs hatch, immature nymphs that look similar to an adult emerge. These immature nymphs molt or shed their skin 4-5 times. The skin that they shed is white and is left on leaves. The white skin casts may look like whiteflies from far so you should take a close look.
7. Ants gathered around the clusters of aphids
Ants can be frequently found around aphids because they ‘farm’ aphids to feed on the honeydew that they produced. These ants protect the aphids from predators and parasitoids to increase their populations and keep getting honeydew, which makes the biological control of aphids challenging. Ants can also move the aphids from plant to plant.
8. Leaves and stems that look like they have been speckled or coated with a thin black film
This substance that can be seen on leaves and stems, which makes it appear that they have been speckled or coated with a thin black film is black sooty mold, a type of fungi. This type of fungi can be wiped off from the leaf surfaces as it does not directly injure the plant but may reduce the amount of photosynthesis and with it, plant growth.
The growth of the fungus can be stopped by controlling the insects that are secreting the honeydew. If the affected plant doesn’t have an insect problem, the honeydew could be falling off from another plant above it.
Once you have determined that your plants have aphids on them, it’s time to get to work and get rid of them.
A few aphids feeding on your plants will not be able to directly cause much damage but they can indirectly kill your plant. This is because aphids can inject plant viruses into the plant as they pierce the plant with their mouthparts to suck out the sap. This makes it important to get rid of aphids as soon as possible.
You should observe your plants for signs of aphids and other plant problems at least twice a week. Look closely under plant leaves where aphids and many other plant pests hide.
The first line of defense is spraying the affected plants with a high force of water to knock aphids off the plant. This must be repeated once a day for a couple of days until aphids are no longer visible.
Mechanically reducing the number of aphids on your plants will help common predators, such as ladybugs, hoverflies, and big-eyed bugs, as well as the aphid midge, a small long-legged fly that feeds only on aphids, control aphid populations. Growing nectar-rich plants with small flowers, such as dill, parsley, and, yarrow will help attract these predators into your garden so that they can swing into action asap.
If aphids are still on your plants or they seem to be protected by ants, you can spray a homemade pest spray such as garlic or hot pepper spray or dust your plants with dichotomous earth. These remedies should get rid of both the aphids and the ants.
If you have tried all the options above and it still doesn’t seem to get better, you can use insecticidal soap or neem oil.
As a vegetable gardener, knowing how to identify signs of aphids on your plants and how these signs are related to the activity of aphids will help you to easily get rid of aphids. Getting rid of aphids will help you keep away aphid infestations and viruses that they transmit.