Absence of windbreaks and replanting citrus in solid sets increase density of Asian citrus psyllid populations

Densities of an herbivorous pest may be impacted by landscape and orchard architecture. We present two orchard experiments where the densities of the Asian citrus psyllid (Diaphorina citri) were compared depending on: (1) the presence or absence of a windbreak and (2) if the orchards consisted of a solid set re-planting or an orchard with a mixture of mature and reset-replacement trees. Psyllid abundance was measured on the edges of five orchards. The factor investigated was the presence or absence of a windbreak. We observed significantly fewer psyllids on the edges of orchards with windbreaks as compared to those without windbreaks. We found no significant difference in the number of natural enemies between the edges with or without windbreaks, suggesting that windbreaks do not affect densities of psyllid natural enemies. Also, during two consecutive years, we compared the densities of psyllids on young trees less than 3 years of age in a solid set re-planting versus on resets (trees planted in replacement of dead or huanglongbing-infected trees) present randomly within mature orchards. This was conducted in four orchards and among three citrus varieties. More psyllids were found in the solid set re-plantings as compared with on the resets within mature orchards. To our knowledge, this is the first report to demonstrate that the planting strategy of new trees in orchards may impact the populations of a horticultural pest. Overall our data suggest that establishment and conservation of windbreaks might be beneficial to protect orchards from D. citri. The data also suggest that D. citri populations increase more within uniform landscapes of seedling trees as compared with mature orchards with randomly interspersed young seedlings.