Thrips on a Dwarf Gardenia

Dwarf gardenias (Gardenia jasminoides "Prostrata") and other compact or prostrate gardenia cultivars grow in U.S. Department of Agriculture plant hardiness zones 8 through 10 as ground covers or small shrubs. They have evergreen foliage and fragrant white flowers. Various insects may bother a dwarf gardenia, including several species of thrips, whose damage you'll usually notice before you see the insects responsible.

Thrips feed on the flower buds and furled leaves of dwarf gardenias and other plants using a rasping mandible to scrape plant cells open and feed on cell contents. Feeding damage appears on expanding leaves as a silvery, white or reddish stippling and a curling or rolling of the leaf, followed by premature leaf drop. Infested gardenia flower buds may die before they open or the flowers may open with deformed, streaked or discolored petals. You may see black specks of excrement where thrips are feeding.

Adult thrips are tiny, slender insects that measure less than 1/20 inch long and have long, fringed wings. Thrips are weak fliers but can float on the wind for long distances. Thrips color varies among species. Immature thrips resemble adults in shape but lack wings. Thrips eggs are relatively large in comparison to the size of the adult female and are cylindrical or kidney-shaped. A magnifying hand lens will make it easier to spot thrips. Holding a sheet of stiff white paper under injured parts of the gardenia and tapping that part of the gardenia will knock thrips onto the paper, which will be barely visible moving around on the paper.

Adult female thrips generally insert eggs into the tissue of leaves or flower buds. The egg squeezes out of the plant tissue just before it hatches and a larva emerges. The larvae go through two stages before pupating in the soil and emerging as adults. When weather is warm, the entire life cycle may take less than two weeks to complete, allowing these pests to have several generations each year. Multiple species of thrips potentially feed on gardenias including Western flower thrips (Frankliniella occidentalis) and flower thrips (Frankliniella tritici). Not all thrips are plant pests. Some species are beneficial, predatory insects while others feed on pollen and fungal spores.

Healthy, vigorous dwarf gardenias can generally withstand and recover from some amount of thrips feeding. Thrips have many natural enemies. Avoid using broad-spectrum, persistent pesticides in the area and occasionally alleviate dusty conditions by spraying the gardenia with water to maintain and encourage thrips predators and parasites. Keep nearby areas free of weeds that can harbor thrips. Provide the dwarf gardenia with good care, including adequate water, and avoid excessive nitrogen fertilizer applications. Blue sticky traps placed around the infested gardenia effectively capture Western flower thrips. If the damage is isolated on just a few sections of the gardenia, pruning off, bagging and disposing of the infested portions can reduce thrips numbers.