Description of the Pest
Sweetpotato whitefly adults are tiny 0.06 inch (1.5 mm), yellowish insects with white wings. Their wings are held somewhat vertically tilted, or rooflike, over the body and generally do not meet over the back but have a gap separating them. Another species that may be present, bandedwinged whiteflies (Trialeurodes abutiloneus), have brownish bands across their wings.
Whiteflies are found mostly on the undersides of leaves. They fly readily when plants are disturbed. The tiny, oval eggs hatch into a first nymphal stage that has legs and antennae and is mobile. The legs and antennae are lost after the first molt and subsequent stages remain fixed to the leaf surface. The last nymphal stage, often called the pupa or the red-eye nymph, is the stage that is easiest to identify.
Last-instar sweetpotato whiteflies are oval and yellowish with red eye spots. The edge of the pupa tapers down to the leaf surface and has few to no long waxy filaments around the edge. In contrast, bandedwinged whitefly nymphs have many long waxy filaments around the edge, and the edge is somewhat vertical where it contacts the leaf surface.
Whiteflies are sucking insects and their feeding removes nutrients from the plant. As they feed, whiteflies produce large quantities of honeydew that reduce alfalfa hay quality because sooty molds (fungi that produce black spores) often grow on honeydew. Sooty molds are not known to harm cattle or horses, but resemble mold from water-damaged hay that produce toxins. Hay buyers are not likely to buy moldy hay or will discount the price of the hay. Sweetpotato whitefly can cause economic damage to alfalfa in the low desert regions of Southern California and Arizona from July through September.
Research continues to focus on developing commercial cultivars with resistance to whiteflies. If insecticides were registered for whitefly control in alfalfa, they would not be cost effective.