Silverleaf Whitefly
Bemisia argentifolii Bellows & Perring

There are several other whitefly species that already occur in landscapes and gardens throughout California. What makes the silverleaf whitefly such a concern is its broad host range and its tendency to rapidly develop extremely high populations. The whitefly has also been associated with some serious viral diseases in other states.

Host range. The silverleaf whitefly has been found on as many as 500 different hosts. Some preferred hosts are canna lilies, bearded iris, crepe myrtle, lantana, petunia, rose and bottle brush. And this may just be the tip of the iceberg! Many plants grown in northern California have not yet been studied for their ability to host the whitefly. However, it is important to note that some common garden plants, especially shrubs and trees, so far have not been affected.

Honeydew and sooty mold. The whitefly feeds by sucking sap from the plant and excretes a sticky exudate called honeydew. When populations are high, honeydew production is copious. Sooty mold often grows on the honeydew, blackening leaf or fruit surfaces.

Stunting and distortion of plant growth. The whitefly's feeding removes nutrients from the plant which results in stunting, poor growth, defoliation, reduced yields, and sometimes death. On certain plants the silverleaf whitefly causes specific damage symptoms such as silvering of leaves on squash, irregular ripening in tomato, whitestalk in broccoli and cauliflower, light root in carrots and white stem in poinsettia.

LIFE CYCLE

The whitefly spends its winters in weeds and ornamental plants, migrating to crops and gardens in spring and summer. Once temperatures warm up in the summer, populations can build rapidly with the highest populations probably occurring in late summer.

Whiteflies lay their tiny eggs on the undersides of leaves. The first stage has legs and antennae, but these are lost after the first molt and the flattened, oval-shaped larvae stay fixed at one feeding site, The last part of the fourth stage immature is the pupa and it does not feed. Adults emerge from the pupae through a T-shaped slit and soon mate and reproduce. There are many generations a year.

HOW TO RECOGNIZE IT

Whitefly adults are tiny (about 1/1 6 inch long) insects that may disperse in clouds when disturbed. Immatures are usually found in colonies on or beneath leaf surfaces. Distinguishing species is difficult and both immature and adults should be examined with a hand lens to confirm identification. Take any suspected silverleaf whiteflies and infested leaves to your county Agricultural Commissioner or University of California Cooperative Extension office to confirm identification.

Adults. Adult silverleaf whiteflies have white wings and a yellow body; they are slightly waxy with no dark markings or bands. Their wings are held somewhat vertically tilted like the peaked roof of a house, instead of flat over their bodies like the greenhouse whitefly. The yellow body is visible between the wings.

Pupae. Pupae of the silverleaf whitefly have no waxy filaments around their edges as do most other species of whiteflies. Most whiteflies produce a lot of white wax in their colonies; silverleaf whitefly has almost none.

MANAGEMENT IN GARDENS

Destroy heavily infested plant parts and alternate hosts. If leaves or plants are heavily infested, prune out infested parts and destroy them before the whiteflies can spread. If infestations become very serious, you may wish to replace heavily infested plants such as lantana, roses, jasmine, honeysuckle and petunia with other plants that are not attacked by the whitefly. Look out for infested weeds and be sure to destroy these as well; pigweed, ground cherry and field bindweed are known to harbor the silverleaf whitefly.

Destroy vegetables at harvest. Tear out and dispose of seasonal vegetables as soon as you are finished harvesting. Old plants can be a source of future infestations. Squash, tomatoes, pumpkins, melons, peppers, cucumbers, eggplant, broccoli, cauliflower, cabbage and okra are especially important hosts of the silverleaf whitefly.

Transplants. The silverleaf whitefly has been brought into new areas on transplants. Be sure to check transplants carefully for whiteflies before you plant them in your garden.

Insecticides. Whiteflies are very difficult to control with insecticides. Repeated applications may make the situation worse by selecting strains of the whitefly that are resistant to pesticides. If insecticide sprays are required, use an insecticidal soap or an insecticidal oil. These will provide partial control of immature whiteflies, but do less harm to natural enemies of the whitefly and other pests. Be sure to spray both the upper and undersurfaces of leaves and get good coverage. Repeat applications will probably be necessary.

Biological control. Whitefly nymphs are preyed upon by bigeyed bugs, lacewing larvae, and other general predators. Several tiny wasps can parasitize the whitefly. A ladybeetle, Delphastus pusillus, is being introduced into southern California to assist in biological control. It is important to preserve these natural enemies by avoiding sprays with broad spectrum insecticides that could kill them. However, at present, natural enemies alone will not control damaging populations of the silverleaf whitefly on their preferred hosts.

Planting times. If the silverleaf whitefly becomes a serious problem in the central valley of California, gardeners may have to adjust planting times for susceptible vegetables to avoid high populations of the pest. For instance, it may be necessary to delay planting fall gardens until migrating whitefly populations have diminished, and spring gardens may be planted early so produce can be harvested before whitefly populations build up in late summer.


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Parts of this material may be reproduced for educational use. Please credit "United States Department of Agriculture, WHITEFLY KNOWLEDGEBASE"