The satsuma (Citrus unshui), also known as the satsuma mandarin or satsuma tangerine, is enjoyed for its easy-to-peel fruits, evergreen foliage, fragrant white flowers, nearly thornless nature and small form. The satsuma is among the most cold-hardy citrus species and is cultivated outdoor in U.S. Department of Agriculture plant hardiness zones 9 through 11, although its small size makes it suitable to keep as a container specimen in even cooler areas. Whether a satsuma is grown indoors in a pot or outside in the ground, it is potentially bothered by various pests and diseases including species of whitefly insects.
Symptoms of Whitefly Feeding
Light whitefly feeding on a satsuma tree may go unnoticed, but a heavy infestation can cause leaf yellowing or drying and drop. Typically most noticeable and problematic, however, is that whiteflies produce a liquid known as honeydew as a byproduct of feeding. Honeydew is a sugary substance that looks shiny or sticky and hosts the growth of unsightly sooty mold. It also attracts ants that feed on the honeydew.
Whiteflies tend to appear in clusters on leaf undersides where they feed on plant sap. The adult insects are tiny, with whitish wings and a yellow body and are covered with a white mealy wax. Immature whiteflies also feed on plant juices and appear as immobile bumps on leaf undersides. The population of this problematic insect increases most rapidly when weather is warm and conditions are dusty. Multiple species of whitefly potentially feed on satsuma including the citrus whitefly (Dialeurodes citri). Citrus whitefly adults are a plain white color, but older nymphs have a Y-shape marking on their backs.
Cultural and Mechanical Controls
Regular monitoring will allow you to recognize a whitefly infestation before the population becomes damagingly large. To control whiteflies, remove leaves that are heavily infested with immobile nymphs and pupae. Adults are knocked off by regularly spraying the infested satsuma with a forceful spray of water. Alternatively, use a handheld vacuum in the early morning to remove whitefly adults and place the vacuum bag in the freezer overnight to kill the pests. Removing all weeds from around the satsuma and other desirable vegetation and spreading a reflective plastic or aluminum foil mulch over the ground can repel whiteflies and is most effective when the satsuma is still small. Whiteflies are drawn to yellow sticky traps, which are commercially available or made at home by painting small squares of cardboard yellow and covering the yellow side with petroleum jelly.
Ants and Other Considerations
Where ants are feeding on the honeydew secreted by the whiteflies, control of the ants is necessary to allow whitefly predators to curb the pest population. Cutting back all satsuma branches that are touching structure or other plants to eliminate bridges and applying a commercially available ant-trapping sticky material in a complete band a few inches wide around the satsuma trunk will trap ants attempting to climb up into the satsuma's canopy. Avoiding the use of broad-spectrum, persistent pesticides on or near the satsuma is very important, as these chemicals have a damaging impact on beneficial whitefly predators and parasites. Chemical treatment of whiteflies is rarely warranted or necessary. Pesticides have limited effects on whiteflies and cultural and mechanical controls are far more effective.