Identification and monitoring
Adult whiteflies are 1 to 2mm, with white waxy wings and pale yellow bodies. They congregate on the underside of leaves and fly rapidly when disturbed. Egg clusters, immature nymphs, and the flattened oval puparia are all found on leaf undersides and are the life stages that indicate an established population.
Yellow sticky traps placed at canopy level are the primary monitoring tool. Adult whiteflies are strongly attracted to yellow and are captured readily on traps. Trap counts above a few adults per week indicate that a population is building.
Whitefly populations can be difficult to find during early establishment because feeding occurs primarily on older leaves in the lower canopy. By the time adults are visible on upper canopy leaves, the population on lower leaves is often significantly larger.
Honeydew, sooty mold, and harvest compliance
The compliance risk from whitefly follows the same pathway as aphids: honeydew deposited on canopy tissue becomes the growth substrate for sooty mold fungi, and the mold colonization contributes to TYM counts at harvest.
The scale of honeydew production is proportional to population size. A moderate whitefly infestation in veg produces manageable levels. A heavy infestation running through flower produces significant honeydew deposits on maturing flower tissue — deposits that the canopy carries to harvest and the testing laboratory detects.
Sooty mold growth on honeydew deposits is visible as a black powdery coating on leaf and bract surfaces. It is distinct from Botrytis and powdery mildew but is equally disqualifying in lab results. Sooty mold does not make the product unsafe to use; it does make it likely to fail the TYM standard.
Virus vectoring by Bemisia
Silverleaf whitefly (Bemisia argentifolii) is a persistent and documented agricultural vector for a range of plant viruses. Lettuce Chlorosis Virus (LCV) has been confirmed in cannabis plants in commercial facilities, and transmission was associated with Bemisia populations. The symptoms — yellowing, mottling, and interveinal chlorosis — closely resemble nutrient deficiencies and are easily misattributed.
This is not the primary risk in most cannabis facilities, but it becomes relevant in facilities near outdoor growing operations or with frequent incoming plant material from multiple sources, where whitefly populations are likely to carry diverse virus pressure.