Citrus trees infected with Huanglongbing (HLB) bacteria become weak and develop dieback, resulting in lost production. These trees eventually decline to a production level that is not economical to maintain in a citrus operation. Sixteen-year-old ‘Valencia’ (Citrus sinensis Macf.) orange trees on Swingle citrumelo rootstock [C. paradisi × Poncirus trifoliata (L.) Raf.], 100% infected with HLB, in decline and losing production, were severely pruned (buckhorned) to stimulate regrowth and the new flush treated with foliar nutritional sprays. Nutritional sprays included the “Boyd cocktail” and two other nutrient treatments that contained phosphites plus nickel and cobalt. Heavily pruned trees and unpruned standard control trees were compared for shoot growth and canopy development.
Citrus is the main fruit tree crop in the world and therefore has a tremendous economical, social and cultural impact in our society. In recent years, our knowledge on plant reproductive biology has increased considerably mostly because of the work developed in model plants. However, the information generated in these species cannot always be applied to citrus, predominantly because citrus is a perennial tree crop that exhibits a very peculiar and unusual reproductive biology.
Citrus greening has devastated the Sunshine State’s orange industry. Researchers and pioneering farmers see cover crops as a road to recovery.
For the last couple of decades, a tiny insect called the Asian citrus psyllid has fed on the stems and leaves of the orange trees in Florida, infecting them with bacteria that cause a lethal disease called citrus greening. The bacterial disease, huanglongbing (HLB), originated in China and has destroyed 90 percent of the state’s groves, devastating its $9 billion citrus industry.
The presence of Diaphorina citri (Asian citrus psyllid, or ACP), the primary vector of the dreaded Huanglongbing disease (HLB, or Asian Citrus Greening), was first reported in east Africa in Tanzania (2015) and Kenya (2016). Surveys that CRI conducted in collaboration with local scientists, confirmed the presence of ACP in the eastern regions of Tanzania. Recently HLB, previously known to occur in some parts of Ethiopia, was detected on the east coast of Kenya (Fig. 1). The recent detection of HLB in Kenya brings it considerably closer to citrus production in Southern Africa. CRI has engaged in a process with Department of Agriculture, Land Reform and Rural Development (DALRRD) to encourage Kenyan partners to scope the possibility of containing and eradicating the disease in the region.
A strong increase in global demand for citrus has so far been evident in the 2020 export season, according to Justin Chadwick, CEO of the Citrus Growers’ Association of Southern Africa.
In a statement, Chadwick said increased global demand for lemons had resulted in 4,5 million 15kg-equivalent cartons being shipped to date. This was double the 1,8 million cartons exported during the same period in 2019.
Assessment of unconventional antimicrobial compounds for the control of ‘Candidatus Liberibacter asiaticus’, the causative agent of citrus greening disease.
In this study, newly identified small molecules were examined for efficacy against ‘Candidatus Liberibacter asiaticus’ in commercial groves of sweet orange (Citrus sinensis) and white grapefruit (Citrus paradisi) trees. We used benzbromarone and/or tolfenamic acid delivered by trunk injection. We evaluated safety and efficacy parameters by performing RNAseq of the citrus host responses, 16S rRNA gene sequencing to characterize citrus-associated microbial communities during treatment, and qRT-PCR as an indirect determination of ‘Ca. L. asiaticus’ viability. Analyses of the C. sinensis transcriptome indicated that each treatment consistently induced genes associated with normal metabolism and growth, without compromising tree viability or negatively affecting the indigenous citrus-associated microbiota.
In organic systems, soil fertility, crop nutrient status, and groundcover management are closely linked. As specified under the National Organic Program (NOP), “Organic producers must rely upon animal manures, compost (organic matter of animal and/or plant origin that has been decomposed by microorganisms), and cover crops to supply some, if not all, of the required nutrients for healthy crops.”
Naturally derived soil amendments have variable nutrient levels depending upon the sources from which they were derived. Therefore, nutrient availability from composts and cover crops will be specific for the soil type and crop demand in each orchard. Besides supplying nutrients, soil amendments can increase soil organic matter, balance pH levels, increase microbial activity, improve soil structure and tilth, improve drainage in clayey soils, improve water-holding capacity in sandy or gravelly soils, and help to suppress some root diseases.Read More
Cover crops can be one component of orchard floor management, but are not a “system” alone. Cover crops are important in maintaining soil structure, encouraging water infiltration, reducing erosion, reducing mud and dust, and maintaining an acceptable driving surface for equipment. A good cover crop can be established with grasses, broadleaf plants such as legumes, or both, although a uniform plant stand is often easier to manage than one made up of multiple crop species. A cover crop should establish itself quickly and thereafter should not require much maintenance. It should be chosen and managed so that competition with trees is minimal.
Grasses are the most common cover crops in orchards. Many different grasses and grass mixtures are available, so orchardists can choose what is best suited to each particular situation. Several low growing perennial rye grasses are available and allow easy orchard access even when headed out.
Response of Navel Lane Late citrus trees to regulated deficit irrigation: Yield components and fruit composition
Response of Navel Lane Late citrus trees to regulated deficit irrigation: Yield
components and fruit composition
The effects of mid-summer regulated deficit irrigation (RDI) treatments were investigated on Navel Lane Late citrus trees over four seasons. Water restrictions applied from July until mid-September were compared
with irrigation at full crop evapotranspiration (ETc). Two degrees of water restrictions were imposed: (1) RDI-1, irrigated at around 50% ETc and, (2) RDI-2, irrigated at 30–40% ETc. In addition, threshold values of midday stem
water potential (Ws) of -1.3 to -1.5 MPa for RDI-1 and of -1.5 to -1.7 MPa for RDI-2 were also taken into account.
Results showed that Navel Lane Late is a citrus cultivar sensitive to water deficit since both RDI strategies reduced fruit size every year and water use efficiency in RDI trees was similar to control trees. However, the RDI-1 strategy allowed water savings up to 19% without reduction in yield when the water stress integral did not surpass 70 MPa day.
Beneficial microorganisms are becoming increasingly important in the biological control of citrus pests, as a complement to the release of auxiliary insects. Proof of this is the research carried out by Koppert Spain, which aims to confirm the efficacy of an entomopathogenic fungus that could help control Trioza erytreae, one of the insects that transmits huanglongbing (HLB), or citrus greening. “Koppert’s objective is to develop a biological solution that may be available to producers if the insect that transmits the HLB arrived in Spain,” said Javier Calvo, researching entomologist at Koppert, in the framework of a Citrus Technical Conference held in El Rompido (province of Huelva) and Palma del Río (province of Cordoba).