thrips

IDENTIFICATION

"Thrips, order Thysanoptera, are tiny, slender insects with fringed wings. They feed by puncturing the epidermal (outer) layer of host tissue and sucking out the cell contents, which results in stippling, discolored flecking, or silvering of the leaf surface. Thrips feeding is usually accompanied by black varnishlike flecks of frass (excrement). Pest species are plant feeders that discolor and scar leaf, flower, and fruit surfaces, and distort plant parts or vector plant pathogens. Many species of thrips feed on fungal spores and pollen and are often innocuous. However, pollen feeding on plants such as orchids and African violets can leave unsightly pollen deposits and may reduce flower longevity. Certain thrips are beneficial predators that feed on other insects and mites.  Thrips can readily move long distances floating with the wind or transported on infested plants, and exotic species are periodically introduced."  (J. A. Bethke, et. al., 2014)

Plant Damage

“Aside from seeking the thrips themselves, or looking for the disease symptoms they can cause, feeding damage may also be revealing. Silvery striations along the leaves are indicative of feeding. They feed on leaves somewhat like the way a person would mow a lawn: back and forth, or round and round, forming a pattern. The silvery patches are actually groups of individual, spent plant cells. The last sign is the presence of fecal matter. The feces show themselves as tiny black specks. Please bear in mind, if you see these signs of feeding damage, you have a great deal of these nasty pests — at least locally on the plant(s) on which the symptoms appear.” (GreenMethods)

Recommended controls for thrips

Each control will have its own set of parameters that will be best suited for individual environments.  Certain controls may only be available for commercial application.

  Commercial farmers are required to reference their own state laws to ascertain if the recommended controls fall within compliance of their states regulatory guidelines.

Beneficial Insects

Biological Controls

Botanical Controls

CHEMICAL CONTROLS

Trap Cropping

Thrips being attracted to a calendula flower at a CHA research site

Thrips being attracted to a calendula flower at a CHA research site

Thrips are capable of being controlled through Trap Cropping. Traditional flowering plants used for thrips are calendula and marigolds. When high densities of thrips are observed in the flower (15-20+ thrips), the flowers can either be removed and discarded or a predator such us Orius insidiosus (Pirate Bug) can be introduced if it is not already observed.

One study had this to say about trap cropping thrips:

“This study shows that keeping marigolds in the greenhouse as thrips traps and Orius habitat will not increase thrips infestation of the crop, if managed properly, and can maintain a population of Orius. Growers that purchase Orius for thrips control spend approximately $50 per 500 plus overnight freight (approximately $30). For greenhouses that have no plant habitat suitable to hold the Orius in the greenhouse, this investment can literally disappear within a few days, so weekly infusions of Orius are required. Some greenhouse growers do indeed make this weekly investment. For small growers, however, regular purchases of Orius are too expensive. By adding Guardian Plants such as marigolds, they can influence the Orius to stay and multiply. Marigold seed is inexpensive, the marigolds are quick to grow and flower, and they happen to also serve as trap plants for thrips. For greenhouse managers already in the business of growing large quantities of plants on schedule, their decision to invest time, materials, space and unique watering requirements in marigolds is balanced against the cost of the Orius. Some growers choose the marigolds or other suitable habitat, while others make regular purchases of Orius. Yet even those growers that make regular purchases are providing habitat to maintain and grow their investment.” (Live Thrips Traps: Using Inexpensive Marigolds to Draw Thrips Away from Greenhouse Crops)

Selected References

Pest Notes: Thrips. UC ANR Publication 7429. Authors: J. A. Bethke, et. al., 2014.

National Center for Appropriate Technology

UCONN - IPM

Oregon State University - IPM