Systemic insecticides enter a plant's sap supply. Aphids seek their nourishment by penetrating the plant's tissue with their sharp mouths to suck the plant's nutrient-rich sap, which makes systemic insecticides highly effective for aphid pest control.
Aphids often congregate in the curling leaves of the plant or high in a tree's canopy. This makes it difficult to reach the insects with insecticidal sprays but using systemic insecticides provides an effective solution to controlling the aphids.
Systemic insecticides are applied to the soil in a granular form and watered in. The plant's root system readily absorbs the insecticide through its roots and it is transported throughout the plant by its sap production. Some systemic insecticides are sprayed on the plant's foliage and absorbed through its cells into its system.
Foliar-sprayed systemic insecticides containing the active ingredient acephate should never be used on food crops because of the toxic danger they pose when they break down. Care should be taken when using soil-applied systemic insecticides containing disulfoton because they are highly toxic to humans, according to the University of California. The systemic insecticide imidacloprid works well to control aphids in trees but needs to be applied two months before the insects occur.