Ultra High Performance Liquid Chromatography – Pesticide Residue Analysis (September 2013 Update) Work continued to compare protocols for analysis of potential insecticide residues in citrus nectar. Analysis of nectar samples collected from early in 2013 continued. More than 100 samples collected were analyzed and the results then compared with laboratories outside UF to compare results. The results from our lab in some cases were comparable to that of outside labs running the same samples, however, over a series of runs, the sensitivity of our analysis decreased such that we lost confidence in the results obtained. After running more samples, the LC-MS ultimately could no longer detect any chemcial standards injected. We are currently awaiting a specialist trouble shooter from Thermo to arrive to assist in diagnosing the problem with the machine.
Report for period ending 3/31/14 Activities of the CHMA program assistant (1/1/14 – 3/31/14): During this reporting period, the CHMA program assistant provided support to the CHMA effort by attending various local CHMA meetings as well as statewide and multi-state meetings. Specifically, Mr. Page attended ten (10) such meetings which included the following: (1/10/14) Volusia CHMA meeting, (1/14/14) Gulf CHMA meeting, (1/15/14) Valdosta CHMA meeting, (1/28/14-1/30/14) Citrus Show in Ft. Pierce, (1/31/14) Hardee CHMA meeting, (2/7/14 – 2/8/14) Alabama fruit and vegetable conference, (2/13/14) East Pasco OJ break, (2/19/14) Hardee CHMA meeting, (3/25/14) Hillbillies, (3/26/14) Dow sponsored CHMA meeting. On 2/20/14, Mr. Page also gave a presentation on the CHMA program for Congressman Tom Rooney who was visiting the area. The presentation informed the congressman of the importance of coordinated psyllid control efforts and the value to the Florida citrus industry. In addition to attending meetings, Mr. Page spent time providing support to the CHMA program by assisting CHMA captains in identifying hotspots of psyllids within their CHMAs, creating seasonal trend graphs for all the CHMAs, and updating the cycle data on the CHMA website. Mr. Page also worked with the computer programmers to rework the CHMA mapping website so that growers no longer must enter a password to view the psyllid count information. This was done to make the website more user friendly.
Entomopathogenic nematodes: Amending soils to increase biological control of insect pests We repeated moisture trials (described in September report) two additional times using both oven dried vs autoclaved soil. We unexpectedly, but consistently, found Catenaria sp. but no other nematophagous fungus survived desiccation in oven dried soil. The series of experiments reported here and in September 2013 demonstrated that S. diaprepesi and H. zealandica survived poorly in saturated soil compared to well-drained soil, whereas only Steinernema sp. survived better in saturated than in well-drained soil. The soil moistures used in these trials did not consistently effect the survival of H. indica. These results from controlled experiments support a recent report (Soil Biology and Biochemistry, 2013, 66:163-174) that the spatial patterns of these four EPN species in Florida citrus orchards were best explained by soil variables related to soil moisture (clay and organic matter content, water holding capacity, depth to groundwater). Comparative proteomic analysis revealed differences in protein expression by S. diaprepesi and Steinernema sp. maintained in well-drained and saturated soil. Detected proteins will be identified by LC-MS-MS to understand mechanisms of habitat adaptation. We found additional evidence for the hypothesis that soil moisture affects EPN community composition by sampling EPNs in 100 field plots from an experiment reported in 2013 (Biological Control 64:26-36). Briefly all four species of EPNs were added to native soil or to sandy soil used to fill tree planting holes in 2007 and again in 2010. The site is poorly drained with groundwater very near the surface and was originally inhabited only sparsely by H. indica. During the 4 year experiment, H. indica and the introduced S. diaprepesi dominated the EPN communities. However samples taken during this December reporting period (3 years after the original experiment terminated) revealed that H. indica and Steinernema sp. are both very abundant in native soil and in sand to the exclusion of S. diaprepesi and H. zealandica. The species specific effect of soil water potential on these Florida EPN natives appears to be the most robust physical variable studied to date for explaining, and potentially manipulating, naturally occurring EPN community structure. Plant parasitic Nematodes: Characterizing a new nematode pest and the prevalence of resistance breaking populations of the citrus nematode. Sampled soil and harvested fruit in 118, 4-tree plots at Ft. Pierce site. Between July and December, the numbers of X. vulgare more than doubled in untreated plots, compared with just a 15% increase in plots treated with oxamyl; however, the difference was not significant (P>0.05). Neither the oxamyl, nor the two experimental compounds reduced numbers of X. vulgare significantly compared to untreated controls. Treatments did not affect fruit yield per tree. However, the incidence of tree loss to citrus greening was especially high (20%) in untreated trees on one of the double-row beds where loss of trees treated with one of the experimental nematicides was just 4.0% (P=0.008). We characterized X. vulgare population densities in 20 sections of a heavily infested grove near St. Cloud and found no relationship between nematodes and either tree condition or root mass density. Soils are being analyzed to determine if there are physical or chemical properties related to the nematode population density or tree quality.
Entomopathogenic nematodes: Amending soils to increase biological control of insect pests EPN communities in the Bartow pH trial were characterized by qPCR in February, Two years after pH was reduced from 7 to 6 or lower by application of elemental sulfur. The composition of EPN communities in untreated and treated plots was similar to that reported in Feb and March 2013. Numbers of S. diaprepesi were nearly threefold higher (NS) and dominated the EPN community (P=0.001; Sd/total EPNs) in sulfur amended compared to non-amended plots. Numbers of H. indica (P=0.001) were sevenfold higher in the non-amended plots. The effects of sulfur were likely independent of EPN infestation by Paenibacillus sp. because the numbers of bacterial spores per plot did not differ between treatments. Although the number of spores per nematode in untreated plots was half that in the sulfur amended plots, the difference was not significant. Effects of EPNs in those plots on sentinel weevils will be evaluated in May. We repeated laboratory assays (reported 12/13) of EPN survival at different water potentials and pH levels. Use of field soil from Bartow experiment produced results consistent with those using soil from the APS experiment. Moisture and pH did not interact for any EPN species. S. diaprepesi and H. zealandica persisted better in dry soil, whereas soil moisture had no significant effect on H. indica or Steinernema sp. in one trial, but saturated soil favored survival of Steinernema sp. in a second trial. Based on the effects of soil moisture and pH on Florida EPN species tested individually, these physical properties appear to be variables that are manageable in orchards in ways that may enhance conservation biological control. We initiated experiments to test whether EPN community structure can be engineered by managing these properties. Mixtures of Sd, Sx, Hi, and Hz were incubated in soil with factorial treatments of low and high pH and low and high water potential. After various times, surviving nematodes were added to columns of soil (maintaining the different soil properties) with weevil larvae. EPNs that recycle in weevils in these columns will be periodically added to fresh columns with weevil larvae for several generations. EPN community composition of each generation in the different soils will be characterized. Field sites will also be identified based on moisture variablilty and soil types to implement field trials that manipulate both moisture and pH. Drafts of two manuscripts were initiated: ‘Soil pH modulates Paenibacillus spore adherance to Steinernema diaprepesi and the longevity of infective juvenile entomopathogenic nematodes’ and ‘Soil water potential and pH structure entomopathogenic nematode communities in microcosms.’ Plant parasitic Nematodes: Characterizing a new nematode pest and the prevalence of resistance breaking populations of the citrus nematode. Treated plots with oxamyl and and two experimental nematicides in Feb-March. Will sample and evaluate effects in May. Analyzed soil texture and fertility in samples from a heavily infested grove near St. Cloud (reported 12/13) and found no relationship with population density of X. vulgare. Established cultures of this species on citrus seedlings in the greenhouse for controlled studies of pathology and comparative root symptomatology. Detected putative resistance breaking biotype of Tylenchulus semipenetrans from orchard on Swingle citrumelo which will be cultured on indicator ‘host range’ rootstocks for comparison to populations recovered from non-Poncirus rootstocks.
Florida growers have reported that enhanced nutritional programs (ENPs) maintain productivity of HLB-affected trees. However, efficacy and sustainability of the nutritional approach for HLB disease management remains uncertain. Complementary studies of multiple ENPs and their individual components compared to the standard nutritional program (SNP) on nursery and field trees were initiated in 2010. ENPs did slow the development of nutrient deficiency in HLB-affected trees, but it did not prevent the development of deficiencies as HLB incidence and severity increased over the 3 years. The slowed nutrient deficiency was not reflected in a slowed yield decline. The trees were 8 years old at the beginning of the study and should have been experiencing yearly yield increases, this stalled for all treatments in the second year harvest and converted to a yield decline in year 3. In both field and greenhouse trees, treatment of HLB-affected trees with ENPs resulted in a reduced fibrous root density compared to trees under the SNP. An opposite trend was observed in healthy trees where those treated with ENPs had a slight increase in fibrous root density compared to SNP. With recent advances in the understanding of HLBs affect on root health, this finding is very concerning. ENP treatment of HLB-affected trees may accelerate fibrous root loss, increasing the susceptibility of the trees to abiotic stress such as drought. In the nursery trial, ENPs reduced the intensity of visual foliar symptoms, but not the percent of canopy with symptoms. Much of this reduction appeared to be attributed to increased HLB associated leaf drop, quantified by comparison of new leaves produced and the final number of leaves on the tree. It is likely that ENP treatments cause symptomatic leaves to drop earlier, improving the general green appearance of the canopy, but not improving the actual health of the tree. In other words, these results suggest that ENPs are masking HLB damage to the tree by decreasing the percentage of canopy with easily visible yellowing, but not improving the biomass or health of the tree, which is reflected in the lack of yield response in the field trial. No changes in infection rate or the speed of distribution through the tree was detected among treatments. However, all treatments containing phosphite did favor earlier infection of the root system compared to the canopy. This was only observed early in infection, during the first or second sampling period in which bacteria were detected in the tree. By 4 months after initial Las detection most trees had bacteria in all tissues tested. The significance of this phosphite effect on early bacterial movement in relation to yield and long-term tree health is uncertain. It is worth noting that the phosphite alone treatment consistently had the lowest yield of all treatments. Looking at all biomass measures (leaf count, leaf area, fibrous root mass, branch and structural root mass) there was a consistent trend that ENP treated trees had the most biomass in healthy trees, but the least biomass in HLB-affected trees. This suggests that ENP treatments are actually dwarfing the growth of HLB affected trees more than the dwarfing and decline caused by HLB alone under SNP. In summary, no improvement in yield or disease progress was observed with any of the ENPs tested. While we confirmed the usefulness of chelated micronutrients for efficient uptake of foliar applied nutrients, they did not prevent HLB-induced nutrient deficiencies. Biomass data suggests that ENPs may have unintended consequences in reducing the abiotic stress tolerance of trees that are already stressed by normal HLB development. The manuscript describing the results of this project is currently under revision for publication in a peer-reviewed journal.
Abandoned citrus groves in US citrus-producing regions are potential sources for both Asian citrus psyllid (ACP), and Candidatus Liberibacter asiaticus (CLas), the bacterium that causes Huanglongbing (HLB). In Florida and Texas where grower-driven area-wide management programs are underway in commercial groves, no psyllid control is being implemented in abandoned citrus. Since ACP adults are highly mobile, they can disperse from abandoned to productive citrus groves. If not controlled, these psyllids will stymie the effectiveness of area-wide management programs aimed at containing the spread of HLB in commercial citrus. ACP is susceptible to a native entomopathogenic fungus, Isaria fumosorosea (Ifr). For our project, we are developing a novel autodissemination system that will inoculate ACP with Ifr and use these infected psyllids to instigate epizootics and rapidly reduce ACP populations in abandoned groves. Our proposed objectives for Year 1 of our project were to evaluate: (1) Impact of Ifr dispensers on ACP populations in abandoned and managed citrus trees, and (2) Effect of time and exposure on Ifr dispensers. However, as of June 30th of 2013, Texas A&M University Kingsville and the Citrus Research Development Foundation were still in negotiation over the contract for this project. As a result, no official work or field activities could be started because neither funding nor contract for our project were in place.
Objective 1: Assays of non-bearing trees soil drenched with the chelated copper formulations Magna-Bon (MB) and Copper Quik (CQ) confirm that copper concentration in leaves of non-sprayed field trees is well above nutritional concentrations. HLB preventative treatments of MB and CQ were applied at 3 month intervals during two growing seasons at 1,2,4,5 or 10 oz/tree in 8 oz of water as soil drenches to visually asymptomatic 1 and 2 year old Valencia trees on Volkamer lemon and Swingle citrumelo, respectively. The solid plantings, located in Sebring and Avon Park, were surrounded by adult trees with 100% incidence of HLB symptoms. After two seasons, leaf samples for determining PCR status of trees in each trial were collected in December 2013 and analysis completed in early 2014. In the 4 year old block of Valencia on Swingle, PCR positive trees across all treatments ranged from approximately 40 to 80% incidence and in the 3 year old block of Valencia on Volkamer lemon ranged from 8-15% incidence. Incidence of PCR positive trees drenched with MB or CQ drenches was not significantly different from untreated trees. Soil copper treatments will be continued in the 3 year old block of Valencia on Swingle for one more season. Second year PCR results are pending from a trial at USDA Picos farm in Ft. Pierce of MB, CQ and copper or zinc phosphite drench treatments of Hamlin on Swingle trees treated since planting.
Abandoned citrus groves in US citrus-producing regions are potential sources for both Asian citrus psyllid (ACP), and Candidatus Liberibacter asiaticus (CLas), the bacterium that causes Huanglongbing (HLB). In Florida and Texas where grower-driven area-wide management programs are underway in commercial groves, no psyllid control is being implemented in abandoned citrus. Since ACP adults are highly mobile, they can disperse from abandoned to productive citrus groves. If not controlled, these psyllids will stymie the effectiveness of area-wide management programs aimed at containing the spread of HLB in commercial citrus. Insecticide-based strategies are not feasible for ACP in abandoned citrus, but biological control of ACP could come from a combination of native or introduced arthropods and pathogens. Two Ifr strains highly pathogenic against ACP and available as spore formulations in the US are the commercial strain PFR97 WDG’ (Certis Inc.,USA) and a south Texas isolate (Ifr 3581). ACP is susceptible to a native entomopathogenic fungus, Isaria fumosorosea (Ifr). For our project, we are developing a novel autodissemination system that will inoculate ACP with Ifr and use these infected psyllids to instigate epizootics and rapidly reduce ACP populations in abandoned groves. Our proposed project objectives for Year 1 were to evaluate: (1) Impact of Ifr dispensers on ACP populations in abandoned and managed trees, and (2) Effect of time and exposure on Ifr dispensers. The efficacy of our management tactic will largely depend on the ability of our Ifr dispensers to attract adult psyllids to the dispensers’ spore-coated surfaces. To obtain an effective attractant for our dispensers, we evaluated blends of synthetic aromatic compounds that replicate the flush volatile profiles of host plants favored by ACP in southern Texas. By September of 2013, we had completed preliminary studies with six proprietary blends and selected the two most promising blends for field trials with our current dispenser design during the fall and early winter of 2013. A third recently developed blend was also selected for the field trials. We compared the number of adult ACP captured by dispensers with sticky surfaces instead of Ifr-spore coated surfaces, when the dispensers were hung in research citrus groves at the Texas A&M Citrus Center and augmented with one of the three proprietary blends. For controls, we used non-augmented dispensers. Three separate consecutive trials were completed during October to December of 2013. We found that the numbers of psyllids captured by dispensers augmented with one of the blends (Blend # 3) was 4 times greater than non-augmented dispensers (controls) and 3 times greater than dispensers augmented with the second most attractive blend. Based on these results, we will be using Blend # 3 for our 2014 field trials with dispensers coated with Ifr-spores. During December of 2013, we contacted the three collaborating USDA-ARS scientists on our project and made arrangements to have them meet with us at the Texas A&M Citrus Center in Weslaco during February 19-21 of 2014. Drs. Christopher Dunlap (USDA-ARS, Peoria, IL), Mark Jackson (USDA-ARS, Peoria, IL, and Joesph Patt (USDA-ARS, Fort Pierce, FL) will be attending the meeting. Our purposes for this meeting will be to evaluate potential field sites and refine project goals, protocols, and time lines. We will also be comparing our current Ifr dispenser design to a new dispenser design that Dr. Patt has been evaluating in greenhouse studies.
Objective 1: Assays of non-bearing trees soil drenched with the chelated copper formulations Magna-Bon (MB) and Copper Quik (CQ) confirm that copper concentration in leaves of non-sprayed field trees is well above nutritional concentrations. HLB preventative treatments of MB and CQ were applied at 3 month intervals during two growing seasons at 1,2,4,5 or 10 oz/tree in 8 oz of water as soil drenches to visually asymptomatic 1 and 2 year old Valencia trees on Volkamer lemon and Swingle citrumelo, respectively. The solid plantings, located in Sebring and Avon Park, were surrounded by adult trees with 100% incidence of HLB symptoms. After two seasons, leaf samples for determining PCR status of trees in each trial were collected in December 2013 and analysis completed in early 2014. In the 4 year old block of Valencia on Swingle, PCR positive trees across all treatments ranged from approximately 40 to 80% incidence and in the 3 year old block of Valencia on Volkamer lemon ranged from 8-15% incidence. Incidence of PCR positive trees drenched with MB or CQ drenches was not significantly different from untreated trees. Soil copper treatments will be continued in the 3 year old block of Valencia on Swingle for one more season. Second year PCR results are pending from a trial at USDA Picos farm in Ft. Pierce of MB, CQ and copper or zinc phosphite drench treatments of Hamlin on Swingle trees treated since planting.
The application of low concentrations (1/4 rate) of Citrus Fix (2, 4-D) and Max-Cel (Cytokinin) with or without ProGibb (GA) very 45 days to Hamlin and Valencia tree canopies at two locations in central Florida for the 2014-15 growing season was completed in October. Trees were again sampled in late fall for phloem development at four locations in the scaffold system (root flare, trunk, small scoffolds and leaf main veins). Fruit drop and fruit per tree data were collected for Hamlin plots and similar Valencia data is being collected now. In one Hamlin test 2, 4-D + Cytokinin with or with out GA had less fruit drop than the Control trees, 11.5 and 13.1, respectively, versus 17 % drop for the Control. Root densities and canopy condition were evaluated and will be reported when the Valencia harvest is finished.
Entomopathogenic nematodes: Amending soils to increase biological control of insect pests In soil columns with moisture gradients, Steinernema diaprepesi migrated toward drier soil and Steinernema sp. toward wetter soil. Both species survived longest at water potentials to which they were attracted (reported previously). Total proteins were extracted from each species and separated by 2D-PAGE Gel electrophoresis after 48 h in wet (18% moisture) or dry (6%) sand. Proteins that were expressed differentially were identified using LC-MS-MS. We hypothesize that a membrane protein(s) senses and initiates responses to moisture levels differentially in each species. In S. diaprepesi, the expression of muscle proteins including paramyosin, actin and LET-99 required for the proper orientation of spindles after the establishment of polarity varied between wet and dry soil. Some energy enzymes, possibly helping the nematode migrate to preferred soil moisture, also varied between the two conditions. Interestingly, we found that some of these proteins in Steinernema sp. varied oppositely in the two conditions, suggesting that it uses some of the same mechanisms to respond differently than S. diaprepesi to soil moisture. Ongoing research seeks to resolve the roles of these and other proteins in pathways by which these nematodes sense and respond to soil water potential. Corporate officers of e-Nema the world’s largest producer of entomopathogenic nematodes toured Florida’s citrus industry for three days. Growers and distributors from the east coast and the central and western flatwoods met with the German EPN producers to describe the market potential for products containing Steirnernema riobrave and S. scapterisci for weevil and mole cricket control, respectively. As a result of these interactions, e-Nema is producing prototype products and attempting to scale up the process to provide a product for managing root weevils in late 2015 or early 2016. While not an objective of the current project, a product with S. riobrave will provide an important supplement to any management options resulting from our research. Catenaria sp. was isolated from a Bartow orchard, cultured and added along with Heterorhabditis indica to the fourth ‘generation’ in the food web experiment as described in the previous report submitted three months ago. Our hypothesis is that the increased complexity will result in EPN communities more congruent with naturally occurring communities. This is an ongoing study to recapitulate naturally occurring EPN communities in response to defined soil physical properties. Plant parasitic Nematodes: Characterizing a new nematode pest and the prevalence of resistance breaking populations of the citrus nematode. Harvested plots in the Fort Pierce trial. There were highly significant (P=0.01) inverse relationships between the dagger nematode population density monitored during the previous two years and both the number of boxes of fruit per plot and the fibrous root mass density. Fruit yield at the highest nematode densities were half those at the least infested plots. Although yields were 25% higher in treated than in untreated plots, the differences were not significant (P=0.26).
We maintained the new colony of Diaprepes abbreviatus, and the nematodes Heterorhabditis bacteriophora, H. floridensis and S. riobrave in anticipation of field experiments during cold events. Selected a site for trials on the UF Gainesville campus to best achieve temperatures low enough to test the proof of concept in the field. No suitable conditions occurred by December 31, trials did occur in January and February 2015 to be included in next report.
Initial research was focused on the development of an artificial feeding system for the Asian citrus psyllid and testing this feeding system utility for screening peptides and dsRNAs as oral toxicants. The initial results led to the observation of significant toxicity of orally fed specific dsRNAs targeting and blocking the function of a specific psyllid gene (a total of eight psyllid genes were tested as dsRNA targets). This finding was the basis for initiation of a CRDF crowd-sourcing competition through innocentive’ to identify the best psyllid gene target to advance in a commercializable psyllid control strategy. Further analysis of this target was conducted in collaboration with Dr. Bill Dawson’s laboratory where the most active dsRNA was expressed in citrus phloem using a Citrus tristeza virus (CTV) expression vector. Plants expressing this dsRNA were used in various feeding trials and shown to induce up to 80% mortality in the adult psyllids feeding on individual leaves, but the level of toxicity was highly and positively correlated with the level of psyllid gene dsRNA in the leaf on which the Psyllid fed. In whole plant studies, where a population of ‘Candidatus ‘ Liberibacter asiaticus (CLas) positive psyllids was placed on the dsRNA producing citrus for 14 days and then removed and tested for the presence of CLas, the number of CLas positive psyllids was greatly reduced as compared to controls. Furthermore, eggs laid by these psyllids were allowed to hatch and the nymphs were allowed to feed, develop and emerge as adults. When these adults were tested for CLas a significant reduction in the number of emerged adults carried detectable amounts of CLas as compared to controls. Continued analysis of the effect of this dsRNA on the psyllid supports the interpretation that the dsRNA is adversely affecting the biochemical pathway that in which the targeted gene functions and the research is now being advanced to test the feasibility of using this RNAi approach in a commercially deployable psyllid control strategy. Two manuscripts are prepared for this research; however, there is also a patent application for this work and once complete, the manuscripts will be submitted.
December 2013 The objectives of this proposal are 1) to determine if a) leaf litter biodegradation treatments reduce Guignardia spp. pseudothecia and improve control afforded by routine fungicide applications; b) if biodegradation is affected by the current fungicide application practices; and c) whether the biodegradation treatments will affect current citrus best management practices (BMP); 2) to determine the seasonal dynamics of leaf litter inoculum load in varying management regime intensities and how environment affects pseudothecia production in the leaf litter; 3.) to test if the resistance to black spot in the leaves and fruit in sour orange is correlated and under simple genetic control through laboratory and field testing of progeny of sour orange crosses in both Florida and Australia. Small plots were set up an Immokalee area grove with 5% urea, CaCO3, Soil set, Compost Aid, Soil Set and Compost aid, and an untreated control. Leaves were collected and treated. The samples were collected and are still being processed. To look at the effect of bagasse, the Senior Biological Scientist and the post doctoral associate undertook the controlled experiment portion of this project and then repeated it. This involves an in vitro study of the decomposition of citrus leaves and inactivation of G. citricarpa by various amendments including bagasse including the microbial consortium of fungal and bacterial strains to aid in the decomposition of bagasse and of citrus leaves. Leaves and other components were collected at time zero and at 10 day intervals. At each collection time, leaves and other components were oven dried and weighed. Soil weight, leaf weight, and then the total weight of each box were recorded. Leaf infection by G. citricarpa was verified by plating. Data collection and analysis is ongoing. To begin tests for understanding the genetic and environmental conditions influencing pseudothecia (ascospores) production in P. citricarpa, a culture-based screening method was developed. This technique utilizes double agar culture plates to detect the presence of forcibly discharged ascospores in culture. This high throughput screening technique eliminates the need for individual microscopic examination of culture plates. It will be utilized as a first stage screen in isolate pairings under controlled environmental conditions to determine specific conditions required for pseudothecia production. There are reports of significant resistance to black spot in sour orange types, most notably ‘Chinotto’. The USHRL scion breeding program has a large population of seedlings from crosses between ‘Chinotto’ and the USDA mandarin hybrid selection 1-37-12, which are now fruiting, and have been evaluated for a number of fruit characteristics. Some of these approach commercial fruit quality and it is reasonable to expect that this population may be segregating for resistance to black spot. Ten seedlings of each of 20 selected Chinotto x 1-37-12 hybrids, the two parent genotypes, and the susceptible standard ‘Valencia’ have been developed at the USHRL and are ready for trial exposed to black spot inoculum. We are currently confirming earlier preliminary results in vitro and data collection is on-going. The subcontracting process with the University of Queensland is still on-going. In the mean time, methods have been developed or optimized to collect different spore stages from leaf litter. There have been two rounds of inoculations of citrus germplasm in Bundaberg. Results are expected as the fruit ripen.
Reduction/suppression of fruit infection in citrus trees using foliar applications of soluble copper novel bactericidal formulations in comparison with film-forming copper formulations 1) Standard copper formulations, Kocide 2000, Kocide 3000, Nordox and Champ were less effective than in previous seasons for canker control on Ruby red grapefruit in a season with above average spring and summer rainfall. For example, 2013 fruit canker incidence was ‘ 35% in the copper treatments and ~80% incidence in the UTC compared with 2012 at ‘ 20% incidence in the copper treatments and ~40% in the UTC. 2) Nordox for 5 sprays followed by Magna-Bon at the 100 ppm rate was not significantly less effective than the 1.33 lb of Nordox alone at 50% of the metallic copper per season. 3) Treatments of Nordox 30/30 or Nordox at 0.44 lb combined with Magna-Bon at the 100 ppm rate both at ~50% of the metallic copper per season were significantly less effective than the 1.33 lb rate alone. 3) Magna-Bon at 100 ppm and formulations of Copper Silica Nanoparticle (CuSiNG pH 4, MV1-CuSiNG pH 4, MV2-CuSiNG pH 4) were less effective treatments except than the CuSiNG pH 4 formulated with fixed quaternary ammonium (fixed Quat). 4) The lowest canker fruit incidence achieved with MV1-CuSiNG pH 7 plus Quat was similar to that of the best fixed copper treatments at ~20% of the metallic copper of the fixed copper formulations. 4) For ‘Hamlin’ orange fruit, despite average rainfall, canker incidence on fruit was 44% lower than in the 2012 season due to the overriding effect of HLB on tree vigor and susceptibility of foliage and fruit to infection. As a result, no significant differences among copper formulations were detected in incidence of fruit canker or percentage fruit drop due to canker. Reduction/suppression of inoculum and fruit infection in grapefruit using soil and trunk applications of insecticidal and non-insecticidal SAR inducers 1) Soil drenches of Actigard and season long rotations with Admire and Platinum were effective for suppressing canker and protecting fruit on young Ruby Red grapefruit trees. The control responses were comparable to those obtained with 21-day copper sprays. Best treatment was a rotation of Platinum 75G, Admire Pro and Actigard combined with season long sprays. These findings are congruent with the recommendation to use neonicotinoid insecticides in rotation for psyllid control (Rogers, 2012) and to integrate their use with protectant sprays of copper (Graham and Myers, 2013). 2) Alternatively, SAR inducers may be applied to the trunk as sprays if there is concern with repeated soil applications leading to risk of leaching or biodegradation in soil. Use of non-insecticidal Actigard also addresses potential concerns for neonicotinoids of non-target effects on beneficial insects. 3)Although not as effective as copper, SAR inducers have substantial disease control activity against scab but little or no activity against melanose. They may be useful to maintain control of fruit fungal diseases should copper applications lapse before the end of period of fruit growth as fruit are still susceptible to late season infection. 4) For ‘Hamlin’ orange fruit, despite average rainfall, canker incidence on fruit was 44% lower than in the 2012 season due to the overriding effect of HLB on tree vigor and susceptibility of foliage and fruit to infection. As a result, no significant differences among copper formulations were detected in incidence of fruit canker or percentage fruit drop due to canker. Residual copper activity on fruit as affected by different formulations of copper products, over time after application for young fruiting trees of Ruby red grapefruit. Results have been compiled and the conclusions will be included in the next progress report
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