The bacterial pathogen associated with citrus huanglongbing (HLB) resides in the phloem of affected trees. The widespread abundance of the vector in Florida, the Asian citrus psyllid ( Diaphorina ...citri ), and the location of the pathogen in the tree vascular tissue limits the efficacy of foliar-applied therapies. Trunk injection is a crop protection strategy that applies therapeutic compounds directly into the tree vascular system, enabling their systemic distribution within the tree. However, limited information is available on the most effective methodology for implementing trunk injection at the commercial scale and the extent of damage inflicted by the injection. In this study, 5-year-old HLB-affected ‘Midsweet’ sweet orange ( Citrus sinensis ) trees were injected with the insecticide imidacloprid, the antibacterial oxytetracycline, or water. Injections occurred in Jun and Oct 2020 using three trunk injection techniques. Trees were monitored for external wounding and internal damage associated with injection, as well as tree health, bacterial titers, and yield for two production seasons. Low-pressure injection caused the least damage; however, it was less effective at delivering the tested compounds than medium- or high-pressure injection. Despite causing the greatest extent of external and internal damage at the injection site, injection of oxytetracycline significantly improved tree health, reduced bacterial titers, and increased yield in the two seasons of this study. Imidacloprid injection caused less wound damage but did not result in any lasting benefits to the trees. These results suggest that trunk injection of oxytetracycline could be an effective strategy for managing HLB and that the damage inflicted by this crop protection strategy can be reduced by selecting a suitable injection technique.
Huanglongbing (HLB), which is associated with the phloem-limited bacteria Candidatus Liberibacter asiaticus ( C Las), is a devastating disease that affects citrus trees worldwide. Because of the ...pervasiveness of the bacteria and psyllid vector, the disease is considered endemic in Florida. Although the effects of C Las on tree growth and physiology have been investigated for decades, most studies compared infected and noninfected trees under greenhouse conditions. This study used newly planted field-grown ‘Valencia’ sweet orange ( Citrus sinensis ) trees on two different rootstocks to monitor the distribution and accumulation of C Las in aboveground and belowground tissues following natural psyllid colonization and assess tree physiological responses and biomass reductions under HLB-endemic conditions. Trees were transplanted into the field with individual protective covers (IPCs), which are used to exclude psyllids and prevent infection. Openings were cut in the IPCs of half of the trees; to promote infection, these IPCs were temporarily removed during the main vegetative flushing period when psyllid populations were high. All trees that were exposed to psyllids became infected and displayed the symptoms typically associated with HLB. Throughout the study, higher levels of C Las were detected in the leaves compared with those in the fibrous roots. Trees that were not exposed to psyllids remained noninfected and healthy. After 18 months, a subset of trees was excavated to assess biomass differences between infected and noninfected trees. Infected trees had root system reductions of 37% and shoot system reductions of 20%, thereby significantly reducing the belowground-to-aboveground biomass ratio. Fibrous root loss was 49% and more severe than the loss of the rest of the root tissue. This study is the first to demonstrate the full extent of damage caused by C Las infection under natural HLB-endemic conditions. The results confirm previous observations that suggested fibrous root loss as one of the major consequences of infection and colonization with C Las. They also reinforce the benefits of using IPCs to prevent infection of young citrus trees during the first years of growth in the field.
Traditional foliar spray and soil drench applications of crop protection compounds have been ineffective at managing huanglongbing (HLB) in citrus. Trunk injection is a technique that delivers crop ...protection compounds directly into the tree vasculature, which optimizes compound availability while minimizing drift, runoff, and damage to non-target organisms. Five-year-old HLB-affected ‘Valencia’ sweet orange (Citrus sinensis) trees were injected with the insecticide imidacloprid or the antibacterial oxytetracycline in October 2020 and April 2021. Trees were monitored for tree health, psyllid colonization, bacterial titers, fruit quality, fruit drop, and yield for two production seasons. Imidacloprid injection caused 63% mortality of psyllid adults within one week and reduced progeny survival by 80%, though the efficacy waned within two months. Injection with oxytetracycline significantly improved tree health, reduced bacterial titers, and reduced preharvest fruit drop by more than 3-fold with corresponding increases in yield. Residue dynamics varied by injected compound and tissue analyzed. These results suggest trunk injection could be an effective delivery method for existing or novel therapeutics targeting either the insect vector or the pathogen causing HLB.
Trunk injection is a targeted delivery of pesticides, insecticides, nutrients, or other plant protection materials into the stem or trunk of woody plants as an alternative to spraying or soil ...drenching. Trunk injection has historically been used for disease and pest management of high-value forest tree species or ornamental plants when aerial applications are problematic due to spatial problems and health-related concerns. An interest in using the injection technique for protection of agricultural crops in commercial production systems has emerged more recently, where foliar applications and soil drenches have proven ineffective or pose environmental hazards. This review provides an overview of the basic principles of trunk injection and the plant physiological implications, its current use in commercial agriculture and other plant systems, and associated risks.
Intensive use of external inputs in specialized industrial farming systems has created significant socio-ecological externalities, including water and air pollution from nutrients and pesticides, ...soil erosion and depletion of carbon stocks, biodiversity loss and rising production costs. Ecological intensification is a strategy for reducing reliance on inputs by intentionally designing agroecosystems to harness biological processes and ecological relationships for the sustainable functioning of the system. Incorporating perennials and diversifying systems are two avenues for achieving ecological intensification, and both are characteristics of agroforestry. This preliminary report uses examples of agroforestry in the US state of California as a proof of concept to explore the agronomic and economic feasibility and sustainability benefits of agroforestry in intensive irrigated and temperate farming systems. An exploratory study of farmers experimenting with agroforestry systems and other agricultural professionals identified eight different variants of agroforestry systems being practiced on prime agricultural land in California, ranging from simple use of winter cover crops in orchards to multi-storied cropping systems with integrated grazing. Respondents noted benefits of reduced inputs and production costs, and better nutrient cycling, soil health and pest control. Trade-offs and challenges included increases in labor requirements and management complexity. Knowledge gaps included lack of guidance in biophysical systems design, lack of clarity about economic tradeoffs, and lack of information about ecosystem services benefits. In light of interviewees’ responses, we discuss the constraints and factors needed to foster the successful expansion of agroforestry systems in California and other regions characterized by industrialized farming.
Among surface irrigation systems, long border and furrow are more adaptive to mechanized farming but may cause a non-uniform distribution of water and nutrients. In this study, field experiments were ...carried out in a flat silage corn field in Hebei, China to investigate the uniformity along the length of border or furrow to understand the spatial and temporal distribution characteristics of soil water, electrical conductivity, and nitrate. This will guide irrigation and fertigation management recommendations, land consolidation, and high standard farmland construction. Border and furrow irrigation were tested using fertilizer rates of 750, 600, 450 and 300 kg/ha. Low quarter distribution uniformity (DU
) and storage efficiency (E) were quantified to determine the distribution of soil water and soil nitrate content. The results indicate heterogeneity along the length of the border or furrow is weak for soil water content and is moderate for nitrate content, based on the uniformity coefficient (CV). The average low quarter distribution uniformity of soil water (DU
) was 96.34, there was a significant effect of irrigation type on DU
, and the DU
for border irrigation was 0.8% larger than that for furrow irrigation. The average low quarter distribution uniformity of nitrate content DU
was 79.04, and there was no significant influence of irrigation type and fertilizer rate on DU
. Spatial and temporal distribution analysis showed that the variation of soil water in the 0-60 cm soil layer was larger than that in 60-100 cm soil layer, and the electrical conductivity (EC) and nitrate content gradually decreased with increasing soil depth. There was a decreasing trend in soil EC and nitrate content with decreasing fertilizer rates. The storage efficiency of water (E
) for border irrigation was 56.63, and significantly lower than that for furrow irrigation over the whole growth duration. The nitrate storage efficiency (E
) was 65.47, and there was no significant effect of irrigation type or fertilizer rate on E
. Even with longer borders or furrows of 90 m, the uniformity of water and nitrate along the length of the border or furrow is weak or medium, which can create non-uniform conditions for crop growth. Furrow irrigation may store slightly more water in the top 60 cm of soil compared to border irrigation. Fertilizer rate had no significant effect on the uniformity and distribution of soil water or nitrate.
Key message
Trunk injection causes injury to trees and best practices must be established for use of this technology to manage vascular diseases such as huanglongbing.
Trunk injection is a technique ...for applying plant protection compounds that has demonstrated efficacy for management of huanglongbing (HLB), a bacterial disease which has devastated the Florida citrus industry. Recently, the antibacterial oxytetracycline has been approved for trunk injection in citrus in Florida. Despite its potential for restoring health of HLB-affected trees, little information is available on the trees’ ability to heal and compartmentalize the wounds caused by trunk injection and the interaction with season and other factors. In this study, 5-year-old HLB-affected sweet orange (
Citrus sinensis
) trees were injected bi-monthly to measure seasonal differences in the rate of uptake of injected water and to compare the external and internal wound reaction in both scion and rootstock. Also investigated was the wound reaction after trunk injection of an injectable formulation of oxytetracycline. Injection during spring and summer promoted more rapid wound closure compared to injection in fall or winter, and injection into the scion was less damaging than injection into the rootstock. Although citrus trees effectively compartmentalized wounds inflicted by injection of water, injection of oxytetracycline impeded wound healing and increased internal damage. Application of a fungicide or pruning sealant increased the size of the wound internally and externally. For trunk injection to be adopted for use in commercial citrus orchards, the benefits of injection must outweigh the risks of wounding associated with the application method. This study provides first insight on some of the best practices for effectively utilizing trunk injection in citrus as a crop protection strategy.
Antibiotics in Crop Production Archer, Leigh; Albrecht, Ute; Roberts, Pamela
EDIS,
05/2020, Volume:
2020, Issue:
3
Journal Article
Peer reviewed
Open access
This new 5-page article presents an overview of the use of antibiotics in agriculture. Several of the most severe bacterial diseases of tree fruit and other crops are discussed and their integrated ...management, which includes the use of antibiotics, is described. Antibiotic use for plant disease protection is compared with the use of antibiotics in livestock production, and their future and limitations in plant production are discussed. Written by Leigh Archer, Ute Albrecht, and Pamela Roberts, and published by the UF/IFAS Horticultural Sciences Department.
The final fruit yield and, ultimately, returns a grower receives from any given harvest is directly related to the number of viable flowers that are generated and the proportion of those flowers that ...produce fruit. A grower can improve the ability for their trees to consistently produce a profitable crop of fruit by understanding the steps involved in flowering and controlling the transition to reproductive growth. This new 6-page publication of the UF/IFAS Horticultural Sciences Department was written by Leigh Archer, Miurel Brewer, Bikash Adhikari, Eduardo Esteves, Christopher Vincent, and Tripti Vashisth.https://edis.ifas.ufl.edu/hs1399
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