Relationship of flower thrips to hardlock of cotton.

摘要

Hardlock is a limiting factor for cotton yields in Florida, and appears as a failure of the fiber to expand outward following boll opening. Annual losses are typically 30 to 70% of the crop. Prior research has identified Fusarium verticillioides as a causal agent. It is believed to infect the flowers on the day of bloom, and sustain itself within the developing boll. It was hypothesized flower thrips may increase the chance of infection by carrying the spores into flowers or allowing better access by the pathogen due to their feeding damage.; To determine the extent to which thrips in the field transport F. verticillioides, thrips were captured and placed on media to isolate Fusarium. Approximately 10% of cotton flowers contained thrips that were carrying Fusarium. Frankliniella tritici was the most commonly found thrips species, representing more than 99% of individuals. Similar results were noted in samples from Louisiana, Alabama, and South Carolina. It was also determined that the average relative humidity from 1900 on the day prior to 1000 on the day of sampling was negatively associated with the number of thrips in flowers at 1000.; Field trials were performed to test the ability of insecticide and fungicide applications to reduce thrips numbers and hardlock. Insecticides reduced thrips number and hardlock severity, and sometimes improved yields. The number of thrips in a plot was positively associated with hardlock severity. Greenhouse experiments were performed to test the ability of Fusarium inoculation, thrips, or thrips exposed to Fusarium to cause hardlock. Thrips exposed to Fusarium resulted in the most severe symptoms. The effect of weather on hardlock was also explored. The average temperature between 0000 and 0600 on the day of bloom was negatively associated with hardlock severity in the resulting bolls. These findings demonstrate hardlock is associated with flower thrips and can be reduced by managing thrips numbers. Hardlock incidence is also influenced by temperature, and this information may allow control measures to be used when they would be most effective.