9/27/2021 - By Dr. Tom Reed

It’s no secret that Florida citrus production has decreased significantly since citrus greening (Huanglongbing, HLB) has become prevalent in the state’s groves. Current research recommends a constant soil supply of nutrients to help enhance tree health and productivity of affected citrus. Harrell’s collaborated on multiple studies with Dr. Jude Grosser, University of Florida professor of plant cell genetics, to evaluate POLYON® controlled-release fertilizer (CRF) efficacy in improving HLB-affected trees.

A sweet orange rootstock selection trial for HLB tolerance has utilized Harrell’s POLYON® blends for years with a noticeable improvement in tree appearance. Recently, the large majority of rootstocks produced between six- and seven-pounds of solids per box for both scions (Vernia and Valquarius). Applied every six months, the Harrell’s CRF blends utilized in this study provide a constant supply of macronutrients as well as elevated levels of important secondary and micronutrients over time. HLB has been present throughout trial since 2009, and considering the reduced soluble solids encountered from many commercial groves around Florida, the juice quality data from this trial is quite relevant. The positive results achieved in multiple years are being attributed to the nutrition program. The excellent fruit quality is even being observed on trees with thin canopies.

Additional greenhouse and field studies being conducted by Dr. Grosser have investigated Harrell’s POLYON® blends with enhanced micronutrient concentrations to improve the health of several varieties of HLB-infected citrus trees. Results from these studies indicate CRF blends as the primary or supplemental souce of nutrients can help maintain tree health, good yields, high fruit quality and suppress bacterial populations, which most likely contributes to the improved tree performance

Harrell’s continues to collaborate with Dr. Grosser to improve citrus production, tree health and fruit quality. Harrell's POLYON® blends are engineered to provide nutrients over time at a predictable rate under specified conditions. To find the right POLYON® controlled-release fertilizer product for you, reach out to your Harrell's Rep.

Figure 1:  Typical fruit from CRF fertilizer study with enhanced micronutrients.

Figure 2:  Greenhouse HLB-infected trees after one year: control standard liquid fertilizer (left) and Harrell’s 16-5-10 plus 3x Mn rate (right).