closeup of adult and immature whiteflies on the back of a leaf

Whitefly adults and immatures. Photo: C. Carignan

Updated: April 27, 2021

Appearance

  • Eggs: Tiny, oval, suspended by short stalks on leaf underside, usually about 15 in a characteristic semi-circular pattern. Initially greenish-white, and then turning dark as mature.
  • Nymphs: Tiny, pale green to almost transparent, flattened oval-shaped discs which may or may not have a waxy white covering. There are 4 instars.
  • Pupae: Is the late 4th instar, which ceases feeding, is thicker and more opaque, and has long waxy filaments around the edge of body.     
  • Adults: Resemble tiny white moths with powdery wings, about 1/10th inch in length, triangular in shape when viewed from above because the wings widen from head to tail.
  • Melon foliage covered in honeydew and damaged by whitefly
    Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

    whitefly damage and sticky honeydew on melon leaf
  • Sweet potato whitefly nymph
    Photo: Charles Olsen, USDA APHIS PPQ, USDA APHIS PPQ, Bugwood.org

    Sweet potato whitefly nymph closeup

Life cycle/habits

  • Whiteflies are often introduced to outdoor plants from infested greenhouse-grown transplants. Cold winter weather used to prevent their ability to survive Maryland winters. However, they are overwintering in warmer parts of the state, including Central MD, due to climate change and the increased production of leafy greens through fall and winter under protective plastic and fabric covers.
  • Eggs are typically laid on the newest leaves.
  • Newly hatched nymphs move to a desirable feeding spot, where they fasten on and begin feeding; the other 3 nymph stages are immobile.
  • Both nymphs and adults aggregate, feeding together on leaf undersides by piercing and sucking out cell contents.
  • Nymphs are inconspicuous and easily overlooked, but adults fly up in swarms when disturbed, and then quickly re-land.
  • Whiteflies excrete a sticky substance, known as honeydew.
  • There are several generations each summer.

Host plants

  • Most common greenhouse vegetable hosts are cucumber, eggplant, and tomato.
  • In gardens, there are numerous hosts, the most common are bean, cucumber, eggplant, lettuce, okra, potato, tomato, squash, and sweet potato.

Signs/symptoms

  • Piercing-sucking method of feeding produces stippling of leaves, followed by yellowing; drying and distortion, and premature leaf drop in heavy infestations.
  • Heavy feeding may wilt and stunt plants.
  • A black fungus called sooty mold grows on the honeydew excreted onto leaf and fruit surfaces. Sooty mold can be washed off produce, but interferes with leaf photosynthesis and weakens plants.
  • Whitefly adults and immatures
    Photo: C. Carignan

    whitefly adults and immatures
  • Whitefly on squash leaf

    Whiteflies on underside of squash leaf

Monitoring

  • Before purchase, tap transplants (especially tomato, eggplant and cucumber) and watch for whiteflies taking flight. In the garden, be alert for whitefly swarms, as well as sticky honeydew or the resultant sooty mold on leaves.

Prevention/control

  • Do not introduce infested transplants: inspect before purchasing by disturbing leaves and watching for whitefly flights.
  • Yellow sticky traps will catch some adults.
  • Whiteflies have many predators and parasitoids that suppress numbers as the season progresses. Early problems may clear up. Parasitized whiteflies look like pepper specks.
  • For heavy infestations, insecticidal soap can be sprayed on leaf undersides and repeated as necessary. Avoid spraying in very hot weather or on very stressed plants. Read label carefully.
  • Horticultural oils, neem, and insecticidal soap can be used for nymphs on leaves; pyrethrins are more effective against adults.
  • Control weeds because some may serve as alternative hosts.
  • Avoid continuous planting of favored crops to extend season/harvest, as it enables whiteflies to move from older to younger plants.

Whiteflies grooming
Video: Dr. Mike Raupp