Field evaluation of integrated management for mitigating citrus huanglongbing in Florida

Authors: ZHANG, MUQING - University Of Florida; YANG, CHUANYU - University Of Florida; POWELL, CHARLES - University Of Florida; PASCO, AVERY - University Of Florida; WANG, JIHUA - University Of Florida; HUANG, YOUZONG - University Of Florida; Duan, Ping

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2018
Publication Date: 1/31/2019
Citation: Zhang, M., Yang, C., Powell, C., Pasco, A., Wang, J., Huang, Y., Duan, Y. 2019. Field evaluation of integrated management for mitigating citrus huanglongbing in Florida. Frontiers in Plant Science. 9(1890):1-12. https://doi.org/10.3389/fpls.2018.01890.
DOI: https://doi.org/10.3389/fpls.2018.01890

Interpretive Summary: Citrus huanglongbing (HLB) is currently the most devastating citrus disease and has caused enormous economic losses to many citrus growing regions of the world. Effective strategies against HLB bacterium in citrus production are still limited. Based on our previous accomplishments for HLB control, we implemented an integrated strategy to combat citrus HLB in Florida field trials, which includes chemotherapy, thermotherapy, and additional nutrition treatment to mitigate citrus HLB. The results indicates some chemicals such as penicillin G potassium, Oxytetracycline Calcium Complex and Silver Nitrate were better than the others with cumulative effects shown in year three. While heat and additional nutrition treatments did not eliminate or suppress Las bacteria over the long term, these treatments did positively affect tree growth and recovery in the short term. This three years field evaluation of integrated management provides new insights into HLB control method and strategy.

Technical Abstract: Citrus huanglongbing (HLB) is extremely difficult to control because the Psyllid-transmitted bacterial pathogen resides inside the citrus phloem and the disease is systemic. In Florida, the nine billion dollar citrus industry has been significantly impacted by severe HLB epidemics. To combat citrus HLB, in this study we implemented an integrated strategy that includes chemotherapy, thermotherapy, and additional nutrition treatment in three field trials over three years. In these trials, only trees already showing HLB symptoms with Ct values ranging from 25.1 to 27.7 were selected for treatments. To assess the complex interactions, we used several methods for evaluating the effectiveness of integrated management, including the slopes (b) of the Ct increase (dy/dt), the pathogenic index (PI) and the decline index (DI) from Ct value and tree scores, and the antimicrobial efficacies from PI and DI. This comprehensive analysis showed that most of the tested chemicals were effective to some degree in killing or suppressing the Las bacterium, with higher efficacies seen for Grove B, where citrus trees were severely affected by HLB, and they had a higher number of psyllids, relative to Grove E and P in the first two years. Trunk-injected penicillin G potassium (PEN) was the most effective chemical treatment in all groves, followed by Oxytetracycline Calcium Complex (OXY), and Silver Nitrate (SN) delivered as foliar sprays. Although the steam heat treatment and additional nutrition did not eliminate or suppress Las bacteria over the long term, these treatments did positively affect tree growth and recovery in the short term. Overall, our results provide new insights into HLB control method and strategy for integrated management for HLB epidemic plantations.