Nutrient Management Impacts on HLB-affected ‘Valencia’ Citrus Tree Growth, Fruit Yield, and Postharvest Fruit Quality

Since the first occurrence of Huanglongbing (HLB) in the Florida commercial citrus industry in 2004, fruit yield and yield components of HLB-affected citrus have declined in endemically affected citrus tree groves. Optimal fertilization is thus critical for improving tree performance because nutrients are vital for tree growth and development, and play a significant role in tree disease resistance against various biotic and abiotic stresses. The objective of the current study was to determine whether leaf nutrient concentration, tree growth, yield, and postharvest quality of HLB-affected citrus trees were improved by the split application of nutrients. The four micronutrient application rates were used as fixed factors and the three nitrogen (N) rates were used as random factors for leaf nutrient analyses, tree growth, fruit yield, and postharvest analyses. Significant leaf manganese (Mn) and zinc (Zn) concentrations were detected when trees received foliar and soil-applied micronutrients regardless of the N rates. There was a strong regression analysis of leaf Mn and Zn nutrient concentration and nutrient rates with R2: 0.61 and 0.59, respectively. As a result, a significant leaf area index associated with foliar and soil-applied micronutrient rates had a positive correlation with leaf area index and soil pH with R2: 0.58 and 0.63 during the spring and summer seasons, respectively. Trees that received a moderate (224 kg·ha−1) N rate showed the least fruit decay percentage and total soluble solids (TSS) of 8% more than the lowest (168 kg·ha−1) and highest (280 kg·ha−1) N rates, even though fruit yield variations were barely detected as these micronutrients promoted vegetative growth. Moreover, the TSS to titratable acidity (TA) ratio of foliar and soil-applied micronutrient-treated trees showed 2% and 7% greater values than the foliar-only treated and control trees, respectively. Although micronutrients exacerbated stem-end rind breakdown (SERB), these nutrients significantly improved fruit storage when the fruits were stored for extended periods (8–11 weeks). Thus, moderate N rate, foliar (1×), and soil-applied (1×) micronutrient treatments improved tree growth, fruit postharvest, and fruit storage characteristics

Micronutrients Improve Growth and Development of HLB-Affected Citrus Trees in Florida

Enhanced nutritional programs (ENPs) have improved citrus trees’ growth and development in the era of Huanglongbing (HLB). Studies conducted with variable rates of manganese (Mn) and Iron (Fe) on young HLB-affected citrus trees showed that applying double the standard recommendation increased growth and biomass accumulation. Since HLB is believed to cause deficiency symptoms of micronutrients in citrus trees, it is critical to ensure their optimal levels in the leaves. This could be achieved by soil application of either a Mn rate of 8.9 to 11.5 kg ha−1 as MnSO4 (31%) for young HLB-affected ‘Valencia’ (Citrus sinensis (L.) Osbeck) citrus trees or an Fe rate of 9.6 to 11.8 kg ha−1 as Ferrous sulfate heptahydrate (20%) for ‘Bingo’ (Citrus reticulata, Blanco) citrus trees. Maintaining optimal levels of these micronutrients may enable citrus trees to carry out photosynthetic activities to ensure growth and development. It may also help the tree in the regulation of various physiological processes as part of the antioxidant enzyme Mn-superoxidase dismutase (SOD). Micronutrient manipulation through variable rates of fertilizer application to influence nutrient availability is an important mitigating factor for HLB-affected citrus trees and an integral component of citrus production in Florida

Phosphorus Dynamics in Clementine Mandarin

The study sought to investigate the internal cycling of phosphorus (P) in Clementine mandarin (Citrus reticulata Blanco Clementine). The biomass formation, P concentration, P uptake and accumulation of different organs (bud, flower, fruit, leaf and branches) identified as active organs and found on 1-year-old shoots on fruit trees of bearing age were periodically examined for 2 years. The biomass value was similar between both production seasons. At the beginning of shoot activity, the biomass of annual shoots had a very low rate in the total biomass (0.4%). The biomass increased from 9.7 kg/tree at the beginning of the production season to 62.8 kg/tree at harvest. The P concentrations were in the ranges of 0.11-0.22% in the branches of <1-year-old shoots throughout the 2 years, 0.07-0.15% in the branches of 1-year-old shoots, 0.17-0.31% in the leaves of <1-year-old shoots and 0.13-0.26% in the fruits of <1-year-old and 1-year-old shoots. The total P accumulation at harvest was 82 and 107 g/tree in the first and second years for <1-year-old shoots, respectively, while it was 44 and 48 g/tree for 1-year-old shoots, in the first and second years respectively. The mean daily P uptake amount was determined as 0.4 g/tree for both production years, and the highest daily P accumulation amount was between the fifteenth and twenty-eighth days for both production seasons

Cold Acclimation and Freeze Protection for Florida Citrus

In preparation for winter in Florida, citrus growers must first understand some essential concepts related to protecting citrus from freezing temperatures. Specifically, growers need to know when and how to protect my citrus trees from freeze damage? This two-part question can be answered by looking at each part independently and then developing a freeze protection strategy. Peer reviewed through UF/IFAS Citrus Research and Education Center; published in Citrus Industry Magazine.

Evaluating seasonal soil water dynamics using a simple soil water balance model in northern Ghana

Soil water management is critical for sustainable crop production, particularly in drought-prone environments. A range of strategies can be used to address spatial (need to improve in-situ infiltration) and temporal (need to improve water holding capacity /storage) to increase soil water availability for crop water uptake and improved yield production and productivity. This paper presents the results from field studies of rainfall and run-off monitoring in rainfed maize-based cropping systems in northern Ghana. Rainfall was measured using rain gauges and run-off was estimated using run-off pits in selected fields plots. Long-term 20-year weather data were used in simulation experiments using a deterministic water balance model to represent smallholder rainfed maize crop system. The field studies in the three regions of northern Ghana resulted in the development of regression rainfall-runoff relationships with R2 in the range 0.75 to 0.97 for fields with/without in situ. Further, estimation of size of water conservation/storage structures could be designed based on long-term rainfall-runoff relations to increase timely crop water availability and reduce spatial losses of water through surface runoff

ACP Management With UV-Reflective Mulch and Flush-Timed Sprays

The future of the Florida citrus industry depends on successfully replacing the present bearing tree inventory with new plantings and transitioning them into crop production. This would be a relatively routine process were it not for the ubiquitous presence of huanglongbing (HLB) and its vector, Asian citrus psyllid (ACP)

Effect of Growing Media pH on Performance of Huanglongbing-Affected Young Citrus Trees

Since the advent of Huanglongbing (HLB) disease, Florida’s citrus production has dropped by 70%. HLB-affected trees decline rapidly under high pH growing conditions. Limited nutrient availability at high soil pH has been speculated to be the cause of such rapid decline in HLB-affected trees; however, such decline is not observed in healthy citrus trees. Therefore, the objective of this study was to understand the nutrient uptake, physiological, and molecular responses of healthy (HLY) and HLB-affected (HLB) sweet orange (Citrus sinensis (L.) Osbeck) trees when grown in media maintained at different pH levels 6.0, 7.0, or 8.0. Overall, the performance of HLY and HLB trees decreased with the increase in pH conditions. HLB trees showed a significant inverse correlation between growth parameters (leaf number, shoot growth, SPAD value, stem water potential) and growing media pH whereas no such correlation was observed for HLY trees. Interesting, superior performance of HLB trees at pH 6.0 coincided with higher accumulation of Fe, Mn, and N in whole plant body as compared to high pH treatments. In contrast, HLY tree performance was significantly better at pH 7.0 compared to other pH conditions. At pH 7.0, stress related genes were upregulated in HLB leaves as compared to HLY leaves, indicating the stress response in terms of leaf abscission, reduced growth, and natural aging process was exacerbated in HLB trees at higher pH treatments. Altogether, all the physiological and molecular observations supports an interaction between HLB trees and pH, where HLB trees at pH 6.0 perform better than at higher pH

Effect of Growing Media pH on Performance of Huanglongbing-Affected Young Citrus Trees

Since the advent of Huanglongbing (HLB) disease, Florida’s citrus production has dropped by 70%. HLB-affected trees decline rapidly under high pH growing conditions. Limited nutrient availability at high soil pH has been speculated to be the cause of such rapid decline in HLB-affected trees; however, such decline is not observed in healthy citrus trees. Therefore, the objective of this study was to understand the nutrient uptake, physiological, and molecular responses of healthy (HLY) and HLB-affected (HLB) sweet orange (Citrus sinensis (L.) Osbeck) trees when grown in media maintained at different pH levels 6.0, 7.0, or 8.0. Overall, the performance of HLY and HLB trees decreased with the increase in pH conditions. HLB trees showed a significant inverse correlation between growth parameters (leaf number, shoot growth, SPAD value, stem water potential) and growing media pH whereas no such correlation was observed for HLY trees. Interesting, superior performance of HLB trees at pH 6.0 coincided with higher accumulation of Fe, Mn, and N in whole plant body as compared to high pH treatments. In contrast, HLY tree performance was significantly better at pH 7.0 compared to other pH conditions. At pH 7.0, stress related genes were upregulated in HLB leaves as compared to HLY leaves, indicating the stress response in terms of leaf abscission, reduced growth, and natural aging process was exacerbated in HLB trees at higher pH treatments. Altogether, all the physiological and molecular observations supports an interaction between HLB trees and pH, where HLB trees at pH 6.0 perform better than at higher pH

Understanding the Fate and Persistence of Herbicides in Soils

Chemical weed control, using herbicides to manage weeds, is an important production practice in citrus groves. Herbicides applied in groves can end up in the soils when the spray hits the soil surface or when herbicides or their metabolite (degradation products) are released from decomposing weed tissues. Subsequently, their fate and persistence in citrus groves are determined by processes such as soil binding, leaching, and degradation. Understanding these processes helps growers in selecting an effective chemical weed management strategy while minimizing the impacts on the crop and environment. Peer reviewed through UF/IFAS Citrus Research and Education Center; published in Citrus Industry Magazine.

Comparison of ACP/HLB management tools for citrus resets

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