Thrips

by Nanette Londeree, Master Rosarian

SIGNS

Tiny, slender adult insects, less than 1/20 inch long, translucent white or yellowish to dark brown or blackish with long fringe around the margins of their wings
Larvae similarly shaped with a long, narrow abdomen and no wings

SYMPTOMS

Stippling on leaf surfaces that may become papery
Black specks of feces around stippled leaf surfaces
Flower buds that are deformed and fail to open
Petals covered with brown streaks and spots
Distorted plant parts

CAUSE

One of the species of Thrips, order Thysanoptera, most often Western Flower Thrip (Frankliniella occidentalis

OPTIMAL CONDITIONS

Many herbaceous ornamentals (impatiens, petunia); vegetables (cucurbits, pepper); fruits (grape, strawberry); some shrubs and trees (rose, stone fruit)
Prefer to feed in rapidly growing tissue
Spring to early fall; lifecycle may be as short as two weeks during warm weather

TREATMENT

Prevention:

Maintain good cultural practices and plant to attract natural enemies like green lacewings and minute pirate bugs
Keep plants well irrigated and avoid excessive applications of nitrogen fertilizer that may promote higher populations of thrips
Control nearby weeds that are alternate hosts of certain thrips
Select cultivars with sepals that remain tightly wrapped around the bud until just before blooms open

Elimination:

Knock pests off plants with a spray of water
Damage to leaves and blooms may be unsightly but does not usually warrant the use of insecticide sprays
No pesticide provides complete control due to thrips’ tiny size, great mobility, hidden feeding behavior, and protected egg and pupal stages
Narrow-range oil (Sunspray, Volck) and neem oil can be somewhat effective for temporary reduction of populations if applied when thrips are present and damage first appears

GOOD GUY / BAD GUY?

A bad guy if you exhibit roses; mostly a nuisance otherwiseThe photo of Thrips at the top of the page is by Baldo Villegas from the extraordinary website: http://members.tripod.com/buggyrose/irosepests.htm

Scroll to Top