These insecticides are typically mixed with water and then poured around the base of the plant. If mulch is present over the treated area, it should be removed prior to application, but can be replaced afterwards. After application, the soil should be kept slightly moist to allow the insecticide to move through and be absorbed by the roots. There will be some delay between the time of application and the time that the insects will be killed by a soil application of imidacloprid. Normally this will take a couple of weeks if conditions are suitable for root uptake (warm temperatures, moist soil).
Once the insecticide has moved inside the plant, these treatments will usually be able to kill aphids and other susceptible insects for several weeks, perhaps dating data a couple of months. This long persistence can provide very good control of aphids. However, it can also increase the potential for harming beneficial insects. In particular, insects that feed on pollen and nectar, such as bees and some natural enemy insects, since imidacloprid can appear in pollen and nectar. To avoid injury to pollinators, soil-applied systemic insecticides should not be applied to plants that are flowering or soon to be flowering.
1 Entomologist and professor at Colorado State University Extension, agricultural biosciences and pest management. 4/96. Revised 1/19.
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