Aphids 411: How to Beat Them in the Garden

Aphids are literally born pregnant and a few dozen aphids will breed into thousands in a matter of weeks.

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Photo by: Image courtesy of Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Image courtesy of Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org

Aphids suck the sap from the leaves, stems, buds and, in some cases, the roots of fruit and vegetable plants, shade trees, ornamentals and flowers leaving them yellowed and distorted.

Aphids (Aphididae), common throughout North America, are small, pear-shaped insects often no larger than a sixteenth of an inch. Using slender mouthparts, aphids feed on fruit and vegetable plants, shade trees, ornamentals and flowers by sucking sap from leaves, stems, buds and, in some cases, plant roots. Although very small, they propagate quickly. Aphids are literally born pregnant and a few dozen aphids will breed into the thousands in a matter of weeks. An uncontrolled aphid population can leave plants yellowed and distorted, impacting both visual appeal and crop production.

The problems aphids bring to the garden are compounded by the ease in which viruses are spread during an aphid infestation and by the growth of sooty mold fungus as a result of the sweet sticky excretions left behind by this common garden pest. That sugary excretion, called honeydew, is not only unsightly and a mold danger, it also leads to an unlikely garden partnership.

The sugar excreted aphids is so attractive to ants they not only feed on the honeydew left behind on plants, they will even use their antennae to “milk” the honeydew from aphids. So valuable is this resource, ants will destroy the eggs of predatory insects like ladybugs or lacewings to protect their charge. When host plants are depleted of nutrients, ants will even carry the often wingless aphids to healthier plants so the cycle may continue. When aphid populations become too dense, aphids will develop wings so they may venture on their own. Even then, ants may be seen tearing the wings from their “cattle” to maintain control. Putting an end to this symbiotic relationship is the first step in controlling an aphid population that may be damaging cultivated plants.

Ants can be discouraged from a garden plot organically by planting repellent herbs like rosemary or geraniums. Sprinkling diatomaceous earth or cinnamon on the site. Spraying dish soap or diluted ammonia can wipe out the scent trails left by ant scouts mapping food sources. Fewer ants will slow the spread of an aphid infestation and encourage the return of those beneficial bugs to reduce their numbers. Ladybugs may even be purchased commercially to quickly re-establish balance.

Contending with aphids already visible plants is a straightforward process. Prune leaves or shoots that are yellowed, curled or otherwise beyond redemption. Using a garden hose, spray plants with a strong stream of water to knock off aphids and wash away residual honeydew.  Most aphids will be unable to return to the affected area. This process should be repeated over a period of days, inspecting plants to ensure the plants remain aphid-free. It is advised to spray plants in the morning to allow plants to dry quickly, reducing the risk of fungal diseases.

Although it is generally unnecessary in a garden that has been appropriately monitored, in extreme cases or if water spraying is ineffective, dish soap or insecticidal soap may be applied to plants. When applying soap, take care to coat both top and bottom of leaves.  Read labels carefully when using any insecticide to ensure it is safe for use on the affected plants. 

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