Beginner

Scientific Name
Frankliniella occidentalis

Identification

• Found in flowers and on fruit.
• Tiny, yellow-brown insects.
• Long and narrow in shape, threadlike.
• Less than 2 mm (1/12 in.) long.
• Nymphs resemble adults in shape and colouring.
• Adults have fringe of hairs on their wings (visible with microscope) .
• Thrips have rasping sucking mouthparts and cause damage by scraping of plant tissue.
• Close inspection of damaged strawberry fruit reveals a necrotic flecking or bronzing of the seeds and fruits, especially beneath the calyx.
•  Symptoms of fruit bronzing occur when king berries reach 5- 10 mm (1/5- 2/5 in.) in diameter.
• The entire fruit may become bronzed and cracked.
• Seeds are prominent.

Often Confused With
Cyclamen mite damage
Two-spotted spider mites
Powdery mildew

Period of Activity
Thrips do not overwinter in Ontario but migrate each spring on air currents from the south.  They are attracted to white flowers and therefore to strawberry bloom that is open when the thrips arrive.  They do not cause problems on strawberries every year.

Scouting Notes
Shake blossom clusters into a white tray or dish.  If high numbers of yellow thrips appear, check developing blossoms and fruit for injury.

Use a hand lens to look closely for thrips.  Breathe gently on blossoms to encourage thrips to move out of the bloom.  Check under the calyx of small green fruit for thrips and rusty discolouration.

ThresholdsWestern Flower Thrips
There are no thresholds established for Ontario.
A threshold of 10 thrips per bloom is used in California.
A suggested limit is 25 thrips/ 50 fruit (PYO) and 5 thrips/ 50 fruit (shipping) in New Brunswick, in Quebec- 2- 10% of fruit with bronzing.

Advanced

Scientific Name
Frankliniella occidentalis

Identification
Thrips are tiny, yellow-brown insects, long and narrow in shape and less than 2 mm (1/12 in.) long.  Adults possess fringed wings but otherwise resemble nymphs in size and shape.  Both adults and nymphs can cause damage.  They are found in blossom clusters and under the calyces of developing fruit.

High numbers of thrips can cause flecking or bronzing of the seeds and fruits, especially beneath the calyx.  The entire fruit may become bronzed and cracked.  Seeds on damaged fruit are prominent.

Often Confused With
Cyclamen mites and two-spotted spider mites (Cyclamen mites and two-spotted spider mites can also cause fruit bronzing.  Distinguish thrips injury from these other disorders by the rusty discolouration on the underside of the sepals.)
Powdery mildew (Powdery mildew can cause fruit to crack and seeds to be raised.  Distinguish thrips injury by the rusty discolouration on the underside of the sepals.)

Biology
Thrips have sucking rasping mouthparts and feed on the developing seeds.  As the fruit expands they feed on the tissue between seeds which results in the death of surface cells and fruit bronzing.  Symptoms of fruit bronzing occur when king berries reach 5- 10 mm (1/5- 2/5 in.) in diameter.

Adult thrips lay eggs in plant tissue.  There are 2 active nymph stages and 2 inactive pupal-like nymph stages.  The entire life cycle is several weeks long and there are numerous generations per year.

Period of Activity
Thrips do not overwinter in Ontario but migrate each spring on air currents from the south.  They are attracted to white flowers and therefore to strawberry bloom that is open when the thrips arrive.  They can be more problematic on day neutral strawberries or other varieties with an extended bloom.  They are frequently problems in greenhouse production of strawberries.

Scouting Notes
Shake blossom clusters into a white tray or dish.  If high numbers of yellow thrips appear, check developing blossoms and fruit more closely.  Use a hand lens to check closely for thrips.  Breathe gently on blossoms to encourage thrips to move out of the bloom.  Take a sample size of 50 fruit/acre at early fruit maturity (5- 10 mm or 1 ½- 2 ½ in. in diameter).

Thresholds
There are no thresholds established for Ontario.
A threshold of 10 thrips per bloom is used in California.
A suggested limit is 25 thrips/ 50 fruit (PYO) and 5 thrips/ 50 fruit (shipping) in New Brunswick, in Quebec- 2- 10% of fruit with bronzing.

Management Notes

• Insecticides applied for control of strawberry clipper weevil and tarnished plant bug sometimes suppress thrips.
• Many beneficial insects, especially minute pirate bugs, feed on thrips.
• Late blooming varieties are often more affected than early varieties.