Tools Available to Growers

Summertime in Florida brings with it an important insect pest on blueberries — chilli thrips. This pest was first recorded in blueberries in Florida in July 2008, and typically feeds on new vegetative growth after post-harvest pruning. Damage on foliage can be significant when there are heavy infestations, and control can sometimes be challenging. Although chilli thrips are familiar to many growers, it’s a good idea to review what we know about it and the control alternatives that are available.

Chilli thrips adults are small (< 1/16 inch in length), around ¾ the size of flower thrips. They have pale yellow bodies with dark fringed wings and dark brown incomplete stripes on the abdomen (Figure 1). The lifecycle of chilli thrips(i.e., egg to adult) is short and typically lasts about 18-20 days at 77-81 OF. Eggs usually hatch in 5-8 days, larvae complete their life stages in 8-10 days, and pupa complete their life stages in 2-4 days on the underside of leaves, in leaf litter, or in soil. Adults live for 20-25 days at 77 OF. 

Chilli thrips are not strong fliers and are only able to move short distances on their own.  However, they can be dispersed over a wide area very quickly due to abiotic factors such as wind or being transported unintentionally by farm workers. They typically form “hot spots” in the fields, moving on to surrounding plants when the amount and quality of foliage available for feeding diminishes. Heavy infestations may occur during prolonged hot and dry periods (June - September) in blueberry.

Figure 1. Adult female chilli thrips.

Photo credits: Babu Panthi

Damage

Chilli thrips feed primarily on young blueberry foliage during late spring, summer, and early fall (usually beginning in June with the first post-pruning foliar flush). Adults and larvae feed on the cell contents of leaves, leading to tissue necrosis and death. Injury symptoms first appear as bronzing along leaf veins and petioles, with leaves gradually curling and distorting (Figure 2). Heavy infestations can cause leaf defoliation with significant curling of leaves. 

Figure 2. Feeding injury caused by chilli thrips feeding on blueberry leaves.

Photo credits: Babu Panthi

Management and Control

Early detection is essential for effective chilli thrips control. Although the appearance of bronzing on new leaves may be the first indication of chilli thrips presence in blueberry fields, by that time damage has already begun to occur. Scouting or monitoring can be done by checking for adults on young leaves with a 10X hand lens, tapping young foliage onto a white sheet of paper, or using white or yellow sticky cards. Chilli thrips may have an irregular distribution within a field, so the sampling area should be random and broad enough to accurately estimate the population in the field. 

An integrated management plan to control chilli thrips includes cultural, biological, and chemical controls. Host plants (including weeds) in or near production fields that support the development of chilli thrips should be removed. Natural predators such as Orius insidiosus (minute pirate bug), which feeds on all life stages of thrips, Amblyseius swirskii (predatory mites), and Geocoris spp. (big-eyed bugs) have shown some effectiveness in managing chilli thrips.

Chemical insecticides are the primary way to manage chilli thrips in blueberry. Insecticides registered for controlling chilli thrips in blueberry include Delegate® (spinetoram), Apta® (tolfenpyrad), Exirel® (cyantraniliprole), Rimon® (novaluron), Assail® (acetamiprid), and Sivanto® (flupyradifurone). Entrust® (spinosad) can be used to manage this pest in organic blueberry production. In a 2020 field trial, Apta® and Assail® were the most effective of the insecticides evaluated. Historically, Delegate® has also been effective against chilli thrips.  Several factors could have affected the effectiveness of Delegate during our 2020 trial, including age and storage of the product prior to use, error in the application rate, and over-use of Delegate in the system. Based on its past performance, we are still recommending the use of Delegate, but we strongly recommend rotation among pesticide classes for all products that growers are using. Delegate has systemic activity, allowing the chemical to be absorbed into plant tissues relatively quickly, and has been shown to be effective in controlling all life stages of chilli thrips. When mixed with Rimon® it prevents egg development and curtails larval activity. A list of products registered for managing chilli thrips in Florida blueberries along with their active ingredients and insecticide classes are provided in Table 1. Be sure to follow all insecticide label instructions, including rotating appropriate products with different modes of action to help minimize the development of insecticide resistance. 

Additional information on chilli thrips can be found in UF EDIS Publication ENY-2053, Chilli Thrips on Blueberries in Florida (https://edis.ifas.ufl.edu/publication/IN1298). 

Table 1. Registered products for managing chilli thrips in Florida blueberries. 

credit:

OSCAR E. LIBURD, Professor and Program leader, Fruit and Vegetable Entomology, University of Florida

DOUG PHILLIPS, Blueberry Extension Coordinator, University of Florida