Advice on Thrips from Berkeley Horticultural Nursery

4 Sep

Tips on Thrips
Thrips has become a major pest in local 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 greater 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 the 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 and a refined Horticultural Oil, at recommended rates. Test the spray on a small portion of the infested plant. If no leaf damage occurs within a few days of your test, proceed to 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 predators.

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.

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