Most thrips in greenhouse are females. Adult females may live for approximately 30 to 45 days and lay from 2-10 eggs per day which are inserted into plant tissue. The first two larval stages remain protected in the tender young growth. After the 2nd instar larvae stops feeding, it migrates to the base of the plants and enters the growing medium to pupate. Adults emerge in two to five days, depending upon temperature. Thrips development occurs between 50˚F and 90˚F. They can survive cooler temperatures than 50˚F; however, there is no development at that temperature.
Begin treating when thrips populations are low. Thoroughly cover all plants parts. Insecticides with contact or translaminar activity are generally used. Repeated applications two to three times every 3 to 5 days (depending upon temperature) may be needed to reduce thrips numbers. Systemic insecticides do not move into the flowers, so only suppress thrips on the foliage.
Adult thrips numbers on cards tend to peak every two to three weeks. Try to time applications before this peak, so adults will be killed before they lay eggs. To successfully manage thrips, it is important to treat using small droplet sprays; repeat applications (two to three sprays about 5 days apart); and treat before you see a peak in adult numbers on yellow sticky cards.
Thrips resistance has been reported to chemical classes organophosphates, carbamate, pyrethroid, and spinosad (Conserve). To delay the onset of insecticide resistance, rotate between insecticides with different modes of action every two to three weeks, or after one generation (depending upon temperature).
Some options for pesticides include:
- Aria (flonicamid - Group 9C), Contact and systemic for thrips suppression.
- Avid (abamectin -Group 6), Contact and translaminar activity.
- Azatin O (azadirachtin- Group 18B), Primarily effective against immature thrips and best used in combination with another product such as Avid.
- Conserve (spinosad - Group 5), Contact and stomach poison. May still work for some growers.
- Mainspring (cyantranilprole- Group 28), Translaminar and systemic activity. Apply as a preventative.
- Mesurol (methiocarb - Group 1A), Contact activity. Reportedly continues to work reasonably well but has 24-hr REI plus it may leave an unsightly residue.
- Overture (pyridalyl-Unknown mode of action), Contact, translaminar and some ingestion activity. Labeled for thrips and caterpillars but may take from 7 to 14 days for control.
- Pedestal (novaluron- Group 15), Insect Growth Regulator (IGR) labeled for immature stages.
- Pylon (chlorfenaphyr - Group 13), Contact with translaminar activity.
- Safari (dinotefuran - Group 4A), (neonicotinoid), Contact and systemic activity.
- Suffoil X (horticultural oil), Contact activity. Thorough coverage important.
- TriStar (acetamiprid - Group 4A), (neonicotinoid) Contact and translaminar activity.
Important - Follow label cautions regarding plant safety.
The Rutgers IR-4 Program has a recent summary of what has been working based upon research reports across the country. According to this report, Mainspring (cyantranilprole), provided excellent control (it must be used preventively) and Aria, Avid, Overture, and Pylon all exhibited good to excellent control.
Photos: Western Flower Thrips and damage
Time for Thrips Already? E-Gro Alert, March 2015
For a complete list of insecticides labeled for use against thrips, see the New England Greenhouse Floriculture Guide.
Tina Smith, UMass Extension and Leanne Pundt, UConn Extension