1. Aphid exuviae on leaves
One of the earliest signs of an aphid infestation is the presence of white casting on the leaves. These are exoskeletons that aphids leave behind after moulting.
Moulting is a biological process that all insects go through in order to make room for new growth. Majority of aphid species go through 4 moults before maturing into an adult. If you spot these white moults on your plants, check the underside of the nearby leaves for an aphid colony.
2. Sticky and shiny leaves
Sticky leaves are caused by honeydew. This is a waste product excreted by all sap-sucking insects. The amount of honeydew production can vary based on the host plant that the aphid feeds from.
Aphids need to consume a large amount of sap to get their daily requirement of amino acids, and in turn, secrete large amounts of carbohydrates in the form of honeydew waste. In fact, they are able to excrete 12 times their body weight in honeydew in just one day.
Honeydew can be a source of black sooty mold and ants (discussed in more detail below).
3. Black sooty mold
Black sooty mold can grow on any surface that has honeydew present. This is a fungal disease that doesn’t infect the plant directly but grows on the surface of the leaf. The dark colored mycelium covers the leaves and intercepts the sunlight, hindering the plant’s ability to photosynthesize. This can lead to chlorosis, stunted growth, and even premature leaf drop.
Many other sucking insects also produce honeydew (leafhoppers, mealybugs, psyllids, whiteflies, softscales etc.)
4. Presence of ants
Honeydew also attracts ants. Some species of ants use honeydew as a food source and will protect entire colonies of aphids against natural enemies in order to secure the supply. If ants are spotted near aphid colonies, they should be exterminated. To learn more about ant control, check out this resource by University of California IPM – Ants control
5. Leaves that are curling or wilting
Aphids tend to target new plant growth which may be due to ease of piercing or high concentration of amino acids available. Some species can cause leaf curling by injecting toxins into the leaf which distorts and curls the new leaves and buds as they grow. Aphid feeding can also lead to gal formations but it’s only caused by a select few species.
Leaf wilt can also be seen in plants with heavy aphid infestations. This usually occurs when a large amount of aphids are feeding on the plant for an extended period of time.
Although aphids rarely kill a mature plant, they can stunt plant growth, decrease yields, and transmit viruses. Suppressing aphid population to acceptable levels is important to keep plants healthy.
In our next blog post, we'll be discussing some natural ways to suppress aphids.
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