University of Maryland Extension

Whiteflies - Vegetables

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Back to leaf yellowing - seedlings and transplants

whiteflies on leaf
Adult whiteflies (Family Aleyrodidae) on leaf
Photo: Central Science Laboratory, Harpenden Archive, British Crown, Bugwood.org

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.

adult whitefly
Closeup of adult whitefly

whitefly nymphs
Whitefly nymphs

Life Cycle/Habits

  • Whiteflies cannot overwinter outside in Maryland's cold temperatures, but may successfully overwinter inside heated greenhouses.
  • They are generally reintroduced to the garden each year from infested greenhouse-grown transplants.
  • 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, most commonly bean, cucumber, eggplant, lettuce, okra, potato, tomato, squash, and sweet potato.

whitefly on squash
Whiteflies on underside of squash leaf

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.


Whiteflies grooming
Video: Dr. Mike Raupp

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.

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