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Comparison of Controlled Release Fertilizer (CRF) for Newly Planted Sweet Orange Trees under Huanglongbing Prevalent Conditions

Tripti Vashisth and Jude Grosser

The Huanglongbing (HLB) endemic has negatively impacted the Florida citrus industry. Currently, 80% to 90% of groves are affected by HLB, and there is yet to be a cure. Over the last few years, several preliminary studies have suggested that a constant supply of nutrients, preferably, all year round, is beneficial for HLB affected trees. These trees tend to look healthier, and produce more yield as compared to trees that do not receive optimal nutritional care. For decades, the use of controlled release fertilizer (CRF) has been demonstrated to be the most efficient strategy that provides constant nutrition to plants all year-round. However, citrus growers are confronted with a variety of CRF options without adequate decision-making information to make the most informed choice with limited budget. Our study was aimed at providing guidance to citrus farmers with regards to the CRF formulations that would be effective under HLB prevalent conditions. We compared five different CRF formulations that are popular among growers, and from three different manufacturers. We tested these formulations on the growth and development of a new plant of Citrus sinensis cultivar, Valquarius sweet orange, on rootstock US-897 under prevalent HLB conditions. The trial was carried out over the span of 4 years and, yields were measured in the fourth year. Using the five different CRF formulations, we found that there were no statistical differences in the yield and fruit quality. However, yields from all treatments were exceptionally high for a 4-year-old tree grown under high disease pressure. Overall, all the CRF formulations yielded good production and fruit quality. All the tested CRF formulations were similar in performance. Therefore, focus should be on constant supply of nutrition in managing groves under HLB prevalent conditions irrespective of manufacturer. Hence, the cost of fertilizer can potentially be a deciding factor for growers in selecting the CRF product for their grove fertilization program.