How To Spot Aphid Damage

Damage from aphid feedings is not uniform and can cause a wide range of symptoms.

by Kevin Fogle
PHOTO: Kevin Fogle

Hungry aphids target most of the common vegetable and fruit crops found in edible gardens across the world. When dealing with aphids, it’s essential to recognize aphid damage to plants in the early stages before their populations grow exponentially.

Most aboveground aphid species seek out the leaves and shoots of young tender plants, sucking out the sap from the vegetation with their needle-like mouthparts. Damage from aphid feedings is not uniform and can cause a wide range of symptoms including:

  • leaves with off-colored spots
  • curled foliage
  • dieback of leaves
  • poor plant growth
  • plant death

The worst aphid damage is often found on young plants, where large aphid populations can quickly overwhelm and kill off new starts.

The plant sap consumed by aphids is not able to be entirely digested by the insects, resulting in a sugary and sticky excretion known as honeydew. Honeydew accumulates on leaves, fruit and anything below plants that have active aphid populations. The sugar content of the excretion makes it an ideal host for several fungi species, collectively known as sooty molds. Growth of sooty mold on foliage can block light to leaves, reduce photosynthesis and cause leaf drop on plants with heavy amounts of the fungi.

The honeydew excreted by aphids not only leads to sooty mold, it also tends to attract several species of ants that form mutualistic relationships with aphid colonies. Ants feed on the sugary honeydew and in return will help physically defend the aphid colony from natural aphid predators, such as ladybird beetles, green lacewings, parasitoid wasps and other beneficial insects. Certain types of ants have even been known to transport aphid eggs to their nests to protect them and ensure the survival of future aphid generations. Thus, ants can be a disruptive factor that prevents aphid populations from being controlled solely by natural beneficial predators in your environment.

Aphids are also a major vector for a wide range of plant viruses. For example, the green peach aphid is known to transmit dozens of viruses, including cucumber mosaic, cauliflower mosaic, potato leaf roll and lettuce mosaic. Even if you have a small aphid population, these pests can do serious harm spreading viruses that cause yellowing, mottling, and retarding plant and fruit growth.

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I strongly recommend doing a spot check inspection of the various plants in your garden each week. On your walk through, look specifically under the leaves or on new plant growth for clusters of the tiny green or yellow aphids. Other telltale clues to keep any eye out for include sooty mold, the plant damage described above, and the presence of ants on your plants. If any of these signs are present, spend a little extra time checking the entire plant for aphids.

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