Economic Injury Threshold of Chilli Thrips (Scirtothrips dorsalis Hood) on Knock Out Rose

Chilli thrips has become an established pest problem for ornamental plant growers and landscape managers in Louisiana and surrounding states. Defining its economic injury levels can help better manage this pest by scheduling insecticide sprays as needed (vs. calendar-based). In this study, we used Knock Out rose ‘Double Red’ to quantify chilli thrips injury symptoms and their relationship with chilli thrips population levels at 0, 3, 5, 15, 30, 50, or 75 thrips per plant. Injury symptoms including brown and grey lesion on leaf surface, dark brown leaf edges, puckering and deformed growth on expanding leaves were evaluated weekly, and a visual damage rating was assigned to plants at 4 weeks after inoculation. Number of leaves, flowers, and thrips, and plant dry weight were also recorded. Results indicated that chilli thrips can injure Knock Out rose at a low initial population (i.e. 3 to 5 thrips per plant) if allowed to develop on newly transplanted plants and left untreated for 4 weeks. Plant growth and quality can be more quickly affected at higher population levels such as 15 and above thrips per plant. If infested, newly transplanted plants need to be treated within 14 days to prevent crop loss from chilli thrips injury.