Western flower thrips (Frankliniella occidentalis) are serious pests that can be found in greenhouses, nurseries, and landscapes. They thrive in warm, dry conditions and feed on a wide variety of plants by sucking out the contents of the plant's cells with their piercing mouthparts. Their feeding also transmits diseases as they feed and fly from plant to plant.
LIFE CYCLE
Adult thrips are tiny, slender winged insects that range in color from pale yellow to dark brown. They have a high reproductive rate and develop in six stages - egg, two larval instars, prepupa, pupa, and adult insect.
First, the small, oval eggs are inserted into plant leaves, petals, and stems. Then the first two larval stages feed on plant tissue before pupating in the ground. Larvae and adults pierce the leaves surface with their sucking mouthparts and feed on plant juices.
DAMAGE
Thrips feeding results in white or silvery gray patches on leaves and petals. When populations grow and damage is extreme, the patches merge together creating large brown areas. The loss of chlorophyll reduces plant vigor and serious infestations can cause the leaves to shrivel. Often, buds fail to open, or only partially open with damaged petals and unsightly flowers. Thrips can also carry certain viruses from infected plants to healthy ones making their control vital.
Inspection of flowers is the fastest way to check for the presence of thrips. Place a sheet of white paper underneath an infected flower. Gently shake the flower to dislodge the insects onto the white paper. The presence of dark fecal specks on the plant also indicates a thrip infestation.
CONTROLLING THRIPS
Since stressed plants are prone to thrips infestations it’s vital to start with healthy plants. Then maintain a healthy crop by providing proper spacing, a clean environment, and drip irrigation vs.
overhead water. Reflective mulches, such as aluminum or silver-colored mulches, can deter thrips by confusing their orientation and disrupting their ability to locate suitable host plants.
Additionally, reduce overwintering sites by removing old crops and weeds. Thrips tend to hide and reproduce in plant debris, so eliminating these potential breeding sites helps disrupt their life cycle.
BIOLOGICAL PESTS
Biological pests are small insects or mites that feed on thrips. They can be purchased from many horticulture companies and usually come in sachets that can be hung on your plants. Amblyseius cucumeris or swirskii are predatory mites often used for thrips. Beneficial nematodes can be used on the pupal stage of thrips. These can be mixed with your irrigation water and applied to the soil around the roots of your plants.
Fungal pathogens, such as Beauveria bassiana, will also kill thrips and other pests. These fungi are naturally occurring in most soils around the world, and don’t negatively impact pollinators. Avoid the use of pesticides since disrupting natural predators with insecticides is often a cause of thrips outbreaks.
There is no one cure for thrips. However, starting with healthy plants, maintaining good sanitation and irrigation, and employing swift multitiered biological and fungal controls can decrease populations.