Skip to content.
Français

Some features of this website require Javascript to be enabled for best usibility. Please enable Javascript to run.

Ministry of Agriculture, Food and Rural Affairs

Thrips

Thrips Thrips adult Thrips damage on cabbage
Click to enlarge.

Beginner

Scientific Names
Thrips tabaci, Frankliniella occidentalis

Identification

  • Small (< 3mm, 1/8 in.), soft-bodied insects
  • Cream to light brown in colour
  • Thrips have sucking-rasping mouth parts and cause tissue damage when they feed on the leaves
  • The plant responds by forming scar tissue at the feeding site, giving the leaf a rough, rusty, warty appearance

Often Confused With
Oedema

Period of Activity
Thrips overwinter on grasses (especially winter wheat) and alfalfa. They migrate into brassica crop fields as the weedy roadsides dry down and the winter wheat and alfalfa are harvested.

Scouting Notes
Monitor for thrips as you walk through the 5 x 5 pattern for other pest counts. Record their presence or absence without an actual count of their numbers. It is important to look for thrips before the cabbage reaches tight cupping as this is the only window for control available to growers.

Thresholds
None established.

Advanced

Scientific Names
Thrips tabaci, Frankliniella occidentalis

Onion thrips are predominant among several thrips that infest brassica crops in Ontario.  This insect is especially damaging to late season cabbage but can also damage the curds of cauliflower and leave them unmarketable.  Not every cabbage field will be infested.  Whether or not this insect presents a problem depends on the surrounding vegetation and on the variety of cabbage grown.

Identification
Thrips are a small soft-bodied insect, less than 3 mm (1/8 in.) in length - about the width of a pencil lead.  They are creamy to light brown in colour.  With a hand lens, their four slender, fringed wings can be seen folded across their backs.  Without magnification, thrips can be identified by their small size and rapid movement.  Because of their small size they can be easily overlooked.  On crops that are susceptible to thrips damage, care should be taken to examine the leaves closely.

Thrips have sucking-rasping mouth parts and cause tissue damage when they feed on leaves.  On cabbage, the plant responds by forming scar tissue at the feeding site and these scars can give the leaf a rough, rusty-looking, appearance.  Severe scarring appears warty.  On cauliflower, the curd can be damaged by thrips feeding.  Light brown to tan streaks will be evident on the white head.  Tissue damaged by thrips feeding is open to attack by disease organisms such as soft rot bacteria and Alternaria.

Often Confused With
Oedema

Biology
Thrips do not survive on cabbage residue in the field during the winter, but rather overwinter on winter wheat and alfalfa.  When they move into cabbage fields, they will first be present on the outer leaves, often on the upper surface.  When the cabbage begins to cup, they move into the heads and seek shelter between the leaves.  Thrips can produce offspring without mating.

The habit of sheltering between leaves is of special concern in storage cabbage.  Thrips can survive in the low temperatures of storage rooms and will continue to feed and damage leaves into the spring. Thrips have been found alive and active on cabbage removed from storage as late as April.

Period of Activity
Early in the season, thrips prefer grasses, especially winter wheat, alfalfa and clover.  They can also be found in abundance along roadside ditches.  As the weedy roadsides dry up and the winter wheat and alfalfa is harvested, the thrips migrate into brassica crop fields. If thrips remain on the crop through the time of storage, they can survive in the low temperatures into the spring. Otherwise, come winter, the small pests will move back into the common overwintering host. 

Scouting Notes
Monitor for thrips as you walk through the 5 x 5 pattern for other pest counts. Record their presence or absence without an actual count of their numbers. Their presence on cabbage is a threat, whether that cabbage is for processing or long-term storage.  It is important to look for thrips before the cabbage reaches tight cupping as this is the only window for control available to growers.

Thresholds
None established.

Management Notes

  • If thrips are a problem in your area, the first line of defence is the use of thrips-tolerant varieties of cabbage.  There are no varieties currently available that are totally resistant to thrips; there are a number of commercial varieties that exhibit various levels of tolerance.  Thrips-tolerant varieties do not repel thrips.  Instead, the thrips do not penetrate as far into the head as they would in susceptible varieties.  As well, these tolerant varieties exhibit less scarring from thrips feeding.
  • It is imperative to control this insect BEFORE it moves into the head for shelter.  Once it has penetrated between the head leaves, it is virtually impossible to achieve coverage adequate for control.  Because of the mobility of this insect, populations will continually move in and out of the field throughout the season.  All blocks should be diligently checked for the presence of thrips at the time of cupping.
  • Weather can also play a role in thrips control.  Frequent rains will physically wash the thrips off the leaves and temporarily reduce the population.