First Sign: Tiny, pure white "moths" resting on leaf surfaces. When disturbed, these moth-like flies quickly flutter up, then settle back down onto plants. Leaves may appear shiny with honeydew. A magnifier reveals clear-white "scales" (the pupae) on the undersides of leaves. All stages of Whiteflies suck plant juices.
Most Common Species: Greenhouse Whitefly & Sweet Potato Whitefly. It's so difficult to be certain which species you have, that we advise either consulting your county agent to be sure, or simply widening your predator strategy to cover both species - it's not uncommon to have both pests together.
Special Species Notes: What finally kills plants with a Whitefly infestation isn't usually the Whiteflies, but a black sooty mold that grows on their accumulated honeydew. By this stage, there'll be clouds of Whiteflies. This is the time to rinse any shiny honeydew off the plants with a strong soapy water spray to prevent sooty mold from growing.
Tiny Whitefly Parasites (Encarsia formosa) lay their eggs inside developing Whitefly pupae, so a Whitefly Parasite hatches out instead of a Whitefly. You'll need a magnifier to see them, but they spell death for Greenhouse Whiteflies, and they provide some limited control of Sweet Potato Whitefly as well.
Whitefly Predators (Delphastus pusillus) eat from 150 up to 600 Whitefly eggs a day! It takes them about 30 seconds to eat a Whitefly egg; slightly longer to eat a larva. They especially prefer the eggs of Sweet Potato Whitefly and Silverleaf Whitefly.
Other Controls: Some customers also report good results with Green Lacewings or Pirate Bugs.
Greenhouse Whitefly Control:
Four Parasite Releases, Two Weeks Apart.
Sweet Potato Whitefly Control:
Six Predator Releases, Two Weeks Apart.
Parasites - 1,000-3,000 per 1,000 Sq Ft.
Predators - 300-500 per 1,000 Sq Ft.
Your Whitefly Parasites arrive packaged, ready to hatch, glued to small, perforated cards which you hang among plant foliage. Parasites work best when temperatures average at least 68 F. (add daytime & nighttime temperatures and divide by 2). Parasites emerge as adults within 2 weeks and fly off to hunt for more Whitefly pupae to parasitize.
Simply shake them out of the container they come in, onto plant foliage. Best at 65 - 90 F.
Sticky Yellow Traps.
Whiteflies are strongly attracted to the color yellow. In fact, you really shouldn't wear yellow clothing around Whiteflies or you're almost sure to carry them from plant to plant. Our Yellow Whitefly Traps are coated with a long-lasting sticky substance and the Whiteflies just fly right to them! This is an excellent secondary tactic, especially when intense infestations need to be knocked down in a hurry.
Do I Have Greenhouse Whiteflies or Sweet-Potato Whiteflies?
Both these whitefly species show up in greenhouses, often at the same time. The difference is important, because whitefly parasites (Encarsia formosa), our least-expensive whitefly control, work better when used against greenhouse whiteflies than when used against sweet-potato whiteflies. With sweet-potato whitefly, additional parasite releases are required (perhaps continuously as often as every 2 weeks), and at higher dosages, and other controls such as Whitefly Predators and Yellow Traps may become needed as well. Monitoring Whitefly Parasite progress against sweet-potato whitefly is also more difficult, because the pupal stages of sweet potato whitefly don't turn "jet" black in appearance like greenhouse whitefly pupa do when parasitized, instead changing only slightly to a milky, somewhat darker color. To really tell these whitefly species apart, it helps to know a little about whitefly biology.
Whiteflies lay eggs on the bottoms of leaves, each one on a short stalk. Eggs are pearly white when first laid, and greenhouse whitefly eggs gradually become brown before hatching, while sweet-potato whitefly eggs age to a dark grey color instead. Young nymphs of both species resemble tiny mealybugs or aphids when first hatched, and don't move very far before settling down to a sedentary existence. After the first molt, they lose their legs and resemble small, white scales. These nymphs are oval, flattened, and appear translucent, with a white, green, or yellowish cast.
After nymphs molt through a total of four 'instar' or growth stages to a pupa-like stage, the adult whitefly emerges through a T-shaped slit cut in the outer skin. All four stages look similar in appearance, growing a little larger with each molt. The last part of the fourth nymphal stage is commonly referred to as the pupal stage. This pupal stage is the most reliable difference between greenhouse whiteflies and sweet-potato whiteflies. The pupa of greenhouse whitefly is oval with straight, flat sides that are perpendicular to the leaf surface, forming a distinct "rim" with a fringe of short hairs around the top edge. The sweet-potato whitefly pupa is oval too, but appears more rounded, or dome-shaped from the side view, and lacks the fringe of hairs. Both species have several pairs of longer hairs rising from the top of the pupa, which are usually longer with greenhouse whitefly than sweet-potato whitefly, but these aren't considered reliable for identification.
When resting, adult whiteflies hold their wings differently, another clue in identification. Greenhouse whitefly adults are slightly larger than sweet-potato whitefly adults, and hold their wings fairly flat over their bodies, nearly parallel to the leaf surface. Sweet-potato whiteflies are slightly more yellow, and hold their wings in a peak over their bodies, at a 45° angle to the leaf surface.