Chilli thrips is a foliar pest of strawberry and blueberry causing feeding injury to new growth leading to stunted plant growth and reduced yield. Currently, repeated insecticide applications are made to manage this pest, however, with limited information on the thresholds and sampling techniques, control decisions made to manage this pest might be inaccurate. Thus, the goal of my Ph.D. was to develop a comprehensive sequential sampling plan in strawberry and a fixed-precision sampling plan in blueberry to improve the monitoring and decision making of chilli thrips and possibly reduce unnecessary insecticide applications in these berry crops.
Greenhouse and field-plot studies showed that chilli thrips move slowly from initially infested to adjacent plants once they arrive in the newly transplanted strawberry fields, providing a significant window for management actions to occur until the crop loss becomes severe. In a separate two-year field-plot study, we found that actively growing strawberry plants were able to compensate for the feeding injury caused by initial five, 10, or 20 chilli thrips adults per plant (one, two, or four adults per strawberry trifoliate), when treated with reduced-risk spinetoram, two weeks after the initial infestation compared to when treated four days after the infestation, with no reduction in plant canopy area, fresh plant biomass, and marketable yield of strawberry. This means initial insecticide application can be delayed for two weeks if the chilli thrips population is below an action threshold population. An action threshold of two adults or larvae per strawberry trifoliate was established in strawberry after relating feeding injury with chilli thrips densities in field cage studies. The action threshold was associated with a 10-30% plant injury, an injury level a plant seems to tolerate. Furthermore, 10 and 14 commercial strawberry and blueberry fields were surveyed, respectively, for chilli thrips by collecting leaf samples for two consecutive seasons to assess the spatio-temporal distribution of chilli thrips. Spatial and non-spatial models such as Taylor’s power law, probability distributions, Lloyd’s index, and Spatial Analysis by Distance IndicEs showed an aggregated distribution of chilli thrips within strawberry and blueberry fields. An action threshold-based sequential sampling plan of chilli thrips was developed for strawberry which requires a minimum of four sampling units (one sampling unit = 10 strawberry trifoliates) and a maximum of 27 sampling units to make a control decision. If a decision that no action is necessary is made, it is recommended to resample the field in 14 days. Furthermore, a fixed-precision sampling plan of chilli thrips was developed for blueberry which requires seven sampling units (one sampling unit = 10 young blueberry shoots with four to five leaves each) to estimate a nominal field mean density of 20 chilli thrips per sampling unit for an area of 2-6 hectares. Aggregations of chilli thrips remained stable over time allowing previous sampling sites to be revisited for resampling both in strawberry and blueberry fields. Further research is needed to incorporate population growth model into the management of this pest since cooler nights during early strawberry season seem to affect the growth and survival of chilli thrips. Overall, the impact of chilli thrips in strawberry is likely to increase in future season as early season production is favored but using accurate sampling methods and judicious insecticide applications coupled with ongoing chilli thrips research in Florida berry crops will help producers reduce input costs and remain profitable in an increasingly competitive market.
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