Thrips on the loose in your garden

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Image courtesy of UC Davis

With the onset of warm weather, we’re hearing reports of thrips damage. These destructive insects wreck havoc in gardens, so we’re devoting time to learning more about them.  — The Garden Guru

 

WHAT THEY LOOK LIKE: Thrips are tiny, slender sucking insects that feed on tissue surfaces. Adults are commonly yellowish or blackish and shiny. Thrips have several generations a year. Females lay tiny eggs within leaf tissue or in the curled or distorted foliage caused by feeding nymphs or adults. Pupae can occur on plants where active stages feed, or mature nymphs may drop and pupate near the soil surface. There are Citrus thrips, Cuban Laurel Thrips that feed on Ficus microcarpa (Indian Laurel Fig), flower thrips (they can damage roses and gladiolas) and greenhouse thrips. Thrips seem to like rhododendrons that are drought-stressed, so during warm, sunny, or windy weather, they need regular water and the occasional shower to be less hospitable to thrips.

DAMAGE: They feed on flowers, buds, under leaves, or other hidden areas of growing plant parts such as central terminals. This sneaky habit is what makes it hard to control them. Citrus thrips can occur on most fruit trees, California pepper trees and pomegranate. That infestation is indicated by yellow to brownish scabby feeding scars that form on fruit, often in a ring around the citrus stem. The damage from flower thrips can be discoloration, blasted (brown dry blossoms that fail to open) and stippling. The more common damage seen is the bleaching and stippling of leaves. The once green leaves take on a slivery appearance and when you turn the damaged leaf over you will notice the tiny black excrement specks. They look like tiny drops of oil. The stippling may also resemble similar damage from spider mites and lace bugs.

CONTROLS–

Biological Controls: Beneficial predators such as Dustywings, lacewings (sold in our stores), and predaceous mites will chow down on citrus thrips. Pirate bugs, lacewings, spiders and predaceous mites will help control plant-feeding thrips. Encourage naturally occurring populations of beneficials by controlling dust (hosing off foliage) and avoiding persistent pesticides. Spinosad is a biorational insecticide, which utilizes the fermentation by-products of Saccharopolyspora spinosa (an Actinomycete-yeast!) as it’s active ingredient. It must be ingested to work so it does not affect beneficials and is recommended for thrips, caterpillars, and beetles.

Mechanical Controls: Sticky Blue Thrip Traps can be hung near infested plants. Chemical Controls-Most insecticides have limited success since thrips reproduce year-round and they are protected from sprays by leaf curls or other plant parts that surround them.

For more info and actual pictures of thrips damage please bring a sample of the bug or damage and let Sloat’s senior staff diagnose the problem.

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