11/18/2021 - By Dr. Tom Reed

Conclusion:

Field experiment to investigate the potential of Mn and B overdoses to improve the health of 10-year old HLB-infected Vernia sweet orange on rough lemon trees. Trees were grown on a four-application soluble program that continued throughout trial. Control was the standard soluble program. Additional treatments included soluble program supplemented twice a year with Harrell’s 12-3-9 controlled release fertilizer (CRF) at 0.9 kg/tree (2 lb/tree), B and Mn at 2x and 4x recommended (Tiger-Sul, Florikan) or a combination of 12-3-9 with the 2x micronutrient rates. As expected, all Harrell’s supplemented treatments increased yield compared to the control (not statistically significant), however had no effect on fruit quality. Cycle threshold values indicated reduced bacterial populations in trees receiving supplementation particularly those that received 4x Mn rate. Further studies with Harrell’s CRF fertilizer blends with micronutrient overdoses had similar results including HLB-infected those with Valencia sweet orange on swingle trees and Orie Lee clone/rootstock study. Supplemental applications of CRF containing an enhanced micronutrient package can help maintain tree health, good yields, high fruit quality and suppress Clas populations, which probably contributes to the improved tree performance.

Figure 1: Harrell’s 12-3-9 blend formulation (St. Helena’s).

Figure 2: Tree on left treated with Harrell’s CRF blend + Mn and boron overdoses.