All you need to know about the thrips in your garden
Almost microscopic in size, thrips feed by rasping soft flower and leaf tissue, then drinking the plant juices. Leaf surfaces often take on a shiny silvery or tan cast; on their undersides, you'll find black, varnishlike fecal matter. Thrips infest a wide variety of plants. In severe cases, blossoms and leaves are often twisted or stuck together.
Plants under stress, especially those that are underwatered, are most susceptible to thrips. During dry, hot periods, hose down the leaves of plants that prefer moist environments (such as rhododendrons). Thrips are effectively managed by natural enemies, including ladybugs, lacewings, and predatory mites. Soap sprays can also be effective.
Chemical controls include acephate, diazinon, chlorpyrifos, and malathion.