Description of the Pest
Ash whitefly is commonly found in orchards and may cause damage if not quickly controlled by parasites. Sweetpotato whitefly may become a problem if orchards are bordered by other crops such as cotton or melon, where sweetpotato whitefly is a serious pest. Whitefly adults are tiny (0.06 inch, 1.5 mm long), yellowish insects that derive their name from the white wax covering their wings and body.
While the adults of different species are similar in appearance, the immature stages are more distinctive. The last nymphal stage, often called the pupa or the red-eye nymph, is the stage that is easiest to identify. Ash whitefly pupae have a covering of dense longitudinal wax tufts on the back and short tubercular structures around the edge that exude a glassy wax. Sweetpotato whitefly pupae are oval, whitish, and soft. The edge of the pupa tapers down to the leaf surface and has few to no long, waxy filaments around the edge.
Whiteflies are found mostly on the undersides of leaves. The tiny, elongated eggs hatch into a mobile first stage immature that has legs and antennae. Both legs and antennae are lost after the first molt and subsequent stages remain fixed to the leaf surface. The adults fly readily when leaves are disturbed.
Both the ash whitefly and sweetpotato whitefly occur on pomegranates in California, but ash whitefly is more common. Whiteflies sometimes reach nuisance levels, depositing honeydew on leaves and fruit. If orchards border cotton, such as in Kern County, the sweetpotato whitefly may migrate into pomegranates in July and August in such large numbers that severe damage may result from honeydew and sooty mold.
Parasites control low to moderate infestations in most orchards, particularly for ash whitefly. However pesticide applications may be necessary.
The parasite Encarsia inaron is the most effective biological control agent of ash whitefly. Generalist predators such as lacewings and lady beetles will prey on whiteflies, but are not as reliable at reducing whitefly numbers as parasites.
Check for parasite presence by looking with a hand lens for dark parasitized pupae, empty pupae with round exit holes, and adult parasites. If parasites are present, expect control of whiteflies in a few weeks.
Monitoring and Treatment Decisions
Whiteflies are present at any time of year, but they tend to reach high numbers in July and August. Watch for the tiny, fluttering adults, for the nymphs and pupae on the undersides of leaves, and for honeydew and sooty mold on fruit and leaves. Check also for the presence of parasites.
Treat in late summer or early fall only if numbers are threatening economic damage due to sooty mold and parasites are not adequate for control. In this case, whiteflies can be controlled with buprofezin, foliar imidacloprid (fall only), or soft chemicals with short residuals such as neem (Trilogy).
|Common name||Amount per acre||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|(Movento)||8–10 fl oz||24||1|
|MODE-OF-ACTION GROUP NUMBER1: 23|
|MODE-OF-ACTION GROUP NUMBER1: 16|
|COMMENTS: Apply at early nymph threshold. Good coverage is essential.|
|(Admire Pro)||2.8 fl oz||12||7|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|COMMENTS: Can be disruptive to natural enemies. Do not apply prebloom (during bud elongation; March–April), during bloom (May–August), or when bees are actively foraging. Do not apply when fruit are present (June–October).|
|(Lannate SP)||1 lb||48||14|
|MODE-OF-ACTION GROUP NUMBER1: 1A|
|COMMENTS: Disruptive to natural enemies of mealybugs, caterpillars, soft scales, aphids, and other pests. Use of this pesticide may result in outbreaks of these pests. Methomyl is also toxic to bees and should not be applied when bees are actively foraging.|
|MODE OF ACTION: — (a botanical insecticide)|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.|
|1||Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers ("un"=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).|
|*||Permit required from county agricultural commissioner for purchase or use.|