Thrips are small, slender insects with fringed wings that feed by puncturing plants and consuming cell sap. They belong to the order Thysanoptera. The Western flower thrips (Frankliniella occidentalis) is the most commonly observed species in greenhouse rose plants and summer flowers.
The Western flower thrips, scientifically known as Frankliniella occidentalis, primarily affects herbaceous ornamentals, including rose plants. These pests cause significant damage by stippling and scarring petals, leaves, and other plant parts. Adult thrips appear with a brownish to black body and have thick bristle-like hairs at the tip of the abdomen, with the abdomen extending beyond the wing tips when at rest. The larvae are characterized by their yellow to orange bodies.
Life cycle and damage
The life cycle of thrips includes several stages: egg, two actively feeding larval stages, nymphal stages, non-feeding prepupal and pupal stages, and adult. Females lay tiny eggs inside flower buds, which hatch into larvae that feed on the buds, causing damage. The larvae develop into pupae, which drop into the soil or leaf litter. Pupae then mature into adults, which return to the plant to feed and lay eggs.
The life cycle of the Western flower thrips progresses through several stages: egg, 1st instar, 2nd instar, propupa, pupa, and adult. Under optimal conditions, this complete cycle lasts about two weeks. The damage caused by thrips can be severe, with affected flower buds potentially becoming deformed and failing to open. Petals may exhibit brown streaks and black spots, while young leaves can develop tiny scars and roll back. Severe infestations may result in stunted plant growth.
Favorable conditions
Thrips thrive in hot, dusty, windy, and dry weather conditions. Poor sanitation, such as the presence of dry fallen leaves, weeds, open flowers, and infested flower buds, can exacerbate the problem. Weeds and flowering shrubs or trees around greenhouses can serve as secondary host plants.
Management and control
Monitoring:
Regular monitoring is essential to detect any entry of adult thrips from outside. This can be achieved by using sticky traps and a well-organized scouting system. The detection of even a single adult should prompt immediate chemical intervention before egg-laying occurs.
Cultural practices for managing Western flower thrips include removing fallen plant debris and leaves where pupation occurs and eliminating open flower buds that might attract adults. It's also important to remove weeds that act as alternate hosts. In cases of mild infestations, infested buds should be removed to eliminate eggs, larvae, and adults. Affected plant parts should be disposed of in designated areas to prevent cross-contamination. Additionally, knocking buds in the morning and cutting stems in the evening are recommended, along with showering plants to lower temperatures.
Chemical control
Chemical control should be applied at the first sign of damage or during favorable weather conditions. Careful selection and mixing of chemicals are essential. Controlled showering before chemical application can enhance effectiveness, similar to other contact insecticides. For heavy infestations, applying chemicals to the soil or tuff is recommended to target the pupal stage, ensuring the media is well-moistened for effective chemical penetration.
Source: Greenlife