During greenhouse visits this week, thrips that fit the description of Thrips parvispinus (pepper thrips) were observed on vinca vines. Thrips parvispinus are native to southeast Asia and were first confirmed in the continental US in Florida, in 2020. Pepper thrips have now been observed in several other US states and Canada.
Pepper thrips are small dark thrips; smaller than other thrips. Females and males differ in size and color. Females are approximately 1 mm long, and males are almost half the size at 0.6 mm long. Males are yellow, while the females have a brown head, black abdomen, and a distinctive yellow thorax.
Thrips parvispinus feed on tender young growth but will also feed on flowers. When they feed on the foliage, they leave feeding scars that appear darker than the usual “silvering” feeding damage of western flower thrips. The feeding damage also causes deformation of new growth that resembles broad mite feeding. They are difficult to find on foliage due to their size and ability to hide in the deformed growth and between overlapping petals on the flowers.
There is not much known about how to control Thrips parvispinus, but research from University of Florida has shown that using foliar sprays of Conserve (2 times, 7 days apart) and rotating with Avid plus azadirachtin (2 times, 7 days apart) can help to control pepper thrips. Research on the use of biological control agents such as predatory mites Amblyseius cucumeris and A. swirskii, or predators such as Orius insidiosus and Atheta coriaria, has not been conclusive.
Also observed this week were damaging populations of western flower thrips sweet potato vine. The presence of these thrips was confirmed by visual observation of injury symptoms on plants and adult thrips on yellow sticky cards used for monitoring pests.
Western flower thrips (WFT) are one of the most common and most notorious pests of bedding plants in the greenhouse. They directly injure plants with their feeding, and can also carry viruses that infect many plants and make them unsalable. WFT feed on flowers and foliage by sucking fluids from cells. The feeding scars created reduce the aesthetic quality and marketability of ornamental plants. When WFT feed on developing tissues, affected cells are unable to expand, and mature leaves and petals are distorted. When WFT feed on expanded tissue, affected cells become filled with air, which imparts a silvery appearance. Western flower thrips is also an important vector of tomato spotted wilt virus and impatiens necrotic spot virus.
Biological control of WFT should be started early before populations increase. Commercially available biological control agents include: entomopathogenic nematodes (Steirnernema feltiae), predatory bugs (Orius species), predatory mites (specifically Amblyseius cucumeris and Amblyseius swirskii), as well as Stratiolaepsis scimitus (formerly Hypoaspis miles). Consult your biocontrol agent supplier for more information.
Some of the insecticides available for control of thrips include Aria, BotaniGard, Pylon, Mainspring Overture, Pradia, and Pedestal. Insecticides with contact or translaminar activity are more effective. Make sure to rotate between different classes to prevent resistance development. For more on insecticides available to control thrips please consult theNew York and New England Floriculture Guide (https://www.negreenhouse.org/pest-guides.html ). Make sure to always read and follow insecticide labels.
- Geoffrey Njue, Extension Specialist, UMass Extension Greenhouse Crops and Floriculture Program