Friend or Foe? Thrips

This article was originally written for the April 2021 edition of The Neighborhood Gardener.

Thrips are very small, yellow, black or brown slender insects. They use a "punch and suck" method to damage flowers and ornamental plants.

Thrips damage leaves, buds, flowers, and small fruit. Infested leaves dry out and sometimes have a silver-flecked appearance. Flower buds fail to open or the flowers are deformed. Thrips are at their peak in the spring. Several species of thrips can cause problems in Florida, including the Florida flower thrips, western flower thrips, chilli thrips, and ficus thrips.

Flower thrips Florida flower thrips are native and don't cause as much damage as western flower thrips. Roses and citrus are favorite hosts, particularly for the white varieties. Western flower thrips is an invasive species that attacks many ornamentals and vegetables.

Chilli thrips The invasive chilli thrips attack all aboveground parts of their host plants, but prefer the young leaves, buds, and fruits. Heavy feeding damage turns tender leaves, buds, and fruits bronze to black in color. The abundance of chilli thrips is low in the rainy season, but becomes high during the dry season. They are more active during the summertime.

Ficus thrips The species resembles the Cuban laurel thrips. Adults are generally dark brown. The thrips feed on expanding leaves causing purplish red spots on the lower leaf surface. The leaves become curled and galled.

If you think your plant has thrips, shake the flowers or leaves over a white sheet of paper. You can then use a 10X magnifying glass or hand lens to see them on the paper.

Insecticides can be used for controlling thrips, but several biological control pests have been found to be very effective.

Several arthropods help keep thrips populations under control, including green lacewing larvae, big-eyed bugs, damsel bugs, insidious plant bugs, ladybird beetles, parasitic wasps, other predaceous thrips, and predatory mites.

Also, a fungal pathogen may be purchased and used to reduce thrips numbers. Some thrips are parasitized by insect-parasitic nematodes.

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