How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Whitefly adults are tiny (0.06 inch), yellowish insects with white wings. They are found mostly on the undersides of leaves. The tiny, oval eggs hatch into a first larval stage that has legs and antennae, which will be lost after the first molt. Nymphs are soft, oval, flat, and remain fixed at one feeding site.

Silverleaf whitefly adults immigrating into beet fields may build up to extremely high numbers on the underside of leaves. They fly in great clouds when disturbed.

DAMAGE

In the Imperial Valley,silverleaf whiteflies and sweetpotato whiteflies will feed and deposit eggs on sugarbeets, but the nymphs do not survive to the adults stage. In high populations, whiteflies can damage sugarbeet by sucking sap from plants and causing stunting and wilting. Large populations along with very hot weather may kill young plants. Whiteflies do not appear to be a problem in the San Joaquin Valley. While large numbers of adults may be seen on foliage in fall, especially in sugarbeet fields adjacent to cotton, they do not lay eggs on sugarbeet leaves.

The sweetpotato whitefly is a vector of lettuce infectious yellows virus, an extremely destructive virus of sugarbeet; the silverleaf whitefly, however, is not. The sweetpotato whitefly has been displaced by the silverleaf whitefly, and lettuce infectious yellows is currently not a major concern. Silverleaf whitefly does inject a toxin into the plant as it feeds, which causes the leaf petioles to turn white. Plants recover, however, when whitefly populations decrease with cooler weather in fall.

MANAGEMENT

Whiteflies only periodically need to be managed during fall on young sugarbeets, primarily in the Imperial Valley. Parasites and predators, in conjunction with not planting sugarbeets next to preferred whitefly hosts, are usually sufficient to keep whitefly populations below damaging levels.

Biological Control
Several wasps, including species in the Encarsia and Eretmocerus genera, parasitize whiteflies. Whitefly nymphs are also preyed upon by bigeyed bugs, lacewing larvae, and lady beetles. Silverleaf whitefly is an introduced pest that has escaped its natural enemies. Some indigenous native parasites and predators do attack it but do not keep it below damaging numbers. The lady beetle Delphastus pusillus is being introduced into southern California to assist in biological control.

Cultural Control
When possible, plant sugarbeets at least 1/2 mile upwind from key silverleaf whitefly hosts such as melons, cole crops, and cotton. Maintain good sanitation in areas of winter/spring host crops and weeds by destroying and removing all crop residues as soon as possible. Control weeds in noncrop areas including head rows and fallow fields and harvest alfalfa on as short a schedule as possible. In addition, allow the maximum time between whitefly host crops.

Monitoring and Treatment Decisions
Routinely check field margins for whiteflies; these areas are usually infested first. Be especially alert for rapid population buildup when nearby host crops are in decline. Allow beneficials an opportunity to control light whitefly infestations. If higher populations are present at the field margins than the field centers, then treat only the field margins. This approach will reduce treatment costs and help preserve beneficials in the field.

In the Imperial Valley treatment may be necessary in September if high populations of this pest are immigrating into sugarbeet. No economic thresholds are established. Insecticidal soaps and oils are not as effective as endosulfan and require frequent applications and good coverage. While good coverage is essential with oils and soaps, phytotoxicity may be a problem.

PUBLICATION

UC IPM Pest Management Guidelines: Sugarbeet
UC ANR Publication 3469
Insects and Mites
C. G. Summers, Entomology, Kearney Agricultural Center, Parlier
D. R. Haviland, UC IPM Program, Kern Co.
L. D. Godfrey, Entomology, UC Davis

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