Reduction in Psyllid Populations Using Supplemental Calcium to Trees Grown in High Calcareous Soils.

Citrus orchard producers throughout the world are challenged to find ways to reduce a pest known as the Asian Citrus Psyllid (ACP) that transfers a devastating phloem plugging disease called Huanglongbing (HLB).  This is especially challenging for organic producers that cannot rely on the use of conventional pesticides to combat ACP populations.  The soils in South Texas are heavy clay soils and highly calcareous.  Preliminary studies inadvertently found that compost material high in calcium (Ca) led to decreased ACP populations in the trees where this compost source was applied.  The objective of two separate studies was to determine if supplemental application of soil or foliar applied forms of Ca would reduce ACP populations in trees growing in high calcareous soils.  A randomized split plot design was developed and a ‘mixed model analysis’ was used to evaluate the effects of soil and foliar treatments and their interactions on ACP population densities.  Correlation analysis was established to identify relationships between nutrients and ACP pest densities using least squared means.  We observed a positive correlation between lower ACP infestations in trees receiving additional calcium application when this macro-nutrient was applied to either the soil or to foliage.    Supplemental calcium additions significantly reduced the ACP population in field trials from 16 to 25% compared to equivalent treatment without Ca.  The findings observed in South Texas’ high calcareous soils may be even more pronounced in areas like Florida where soils are sandy and non-calcareous. With an increased threat of HLB disease and other insect related diseases facing citrus growers, we anticipate that this data may allow us to find another aspect of decreasing this threat to the industry without the use of bio-pesticides.  These results are encouraging for organic producers and home owners as a nutritional management plan may lower the spread of HLB disease.