To detect a whitefly infestation, one should:

To effectively detect a whitefly infestation, examining the underside of leaves is critical. Whiteflies typically reside on the lower surfaces of leaves, where they can feed on plant sap and lay their eggs. Their presence is often indicated by tiny, white, winged insects, as well as by the sticky residue they leave, known as honeydew, which can attract other pests and lead to sooty mold.

Inspecting the soil moisture is less relevant for identifying whiteflies specifically, as whiteflies do not typically reside in the soil. While culling affected plants might be a necessary management step after detection, it does not aid in the initial identification of an infestation. Additionally, checking for leaf drop could indicate a variety of plant health issues, but it does not pinpoint the specific presence of whiteflies, which primarily damage the foliage rather than directly cause leaf drop. Hence, looking on the underside of leaves is the most direct and effective method for determining if a whitefly problem exists.