Controlling citrus Huanglongbing based on soil remediation and biocontrol

Huanglongbing (HLB) is a devastating citrus disease that causes significant financial losses in the citrus industry. However, there is no cure by current control strategies. Damaged soils were observed in citrus orchards; root lesions and nematodes were observed in HLB-affected citrus tree roots. Bacillus subtilis (B. subtilis) makes a great contribution to pathogen control and has the potential to control HLB. Purpureocillium lilacinum (P. lilacinum) and Trichoderma harzianum (T. harzianum) can kill pathogenic organisms such as nematodes and Phytophthora spp. to protect roots. Restoration of the damaged soils and improvement of citrus root growth through the introduction of soil amendments and biocontrol agents (containing B. subtilis, P. lilacinum, and T. harzianum) may provide an efficient approach to controlling HLB. Results revealed that soil properties such as soil pH and organic matter content were improved. After three months of combination treatment of soil amendment and biocontrol agent through root drenches, the citrus grew new roots and its leaves changed from yellow to green. The percentage of HLB-positive citrus trees—Orah, Tangerine, and Navel Orange—decreased from 90 to 0%, 87.5% to 21.88%, and 81.25% to 0% over three years, respectively. Furthermore, the productivity of HLB-affected orchards was restored, and both production and quality saw significant improvement. These results suggested that combining soil remediation and biocontrol improved soil quality and protected citrus root growth, thus effectively controlling HLB.