Thrips has become the number one pest in California gardens in recent years. Many people do not realize that their gardens are infested until the leaves of their plants are stippled and silver-colored with thrips damage. Colonies of these tiny sucking insects can be found on the undersides of infested leaves. The tiny white to yellow nymphs and yellow to black adults leave behind black spots of feces. Once leaves are damaged they cannot recover and are best removed.

Most thrips damage occurs during the warmer, drier months of the year. Plants in dry shady locations appear to be more susceptible with the lower leaves at greatest risk. Well-watered healthy gardens and plants with overhead watering tend to be less susceptible. Forceful streams of water on the undersides of infested leaves can help control this pest. Plants most susceptible to thrips include Azalea, Bergenia, ferns, Luma, Pyracantha, Rhododendron, Toyon and Viburnum. Recently Camellias and evergreens have shown damage as well.

The sooner this insect is detected, the easier it is to control. Spray with a solution of Insecticidal Soap or a Horticultural Oil, at recommended rates. Thoroughly spray your plant with special attention to the undersides of leaves and the lower branches. Because of their short persistence, oil or soap sprays are less disruptive of natural enemies.

Nuccio’s Nurseries, a grower of Camellias and Azaleas, uses a spring spraying of Horticultural Oil to control their thrips infestations. Any subsequent outbreaks are controlled by releases of Lacewing beneficial insects which they order from insectaries.

There is evidence that plants with good mulch around their bases are less prone to thrips infestations, and Earthworm Castings are our choice for this. Mulching may provide an environment for natural predators plus improve the overall health of the plant by conserving moisture. Removal of badly infested leaves and any plant debris from around the base of the plant is recommended before spraying.

While there is no magic cure for thrips, keeping a close watch on established plantings, selecting plants that are less susceptible, deep watering during the warm season, and immediate treatment when thrips are first detected will go a long way toward managing this widespread pest.