We have concluded the low volume spray trials testing insecticides in different chemical classes for control of the Asian citrus psyllid. The insecticides evaluated included insect growth regulators, organophophates, pyrethroids, neonicotinoids and one microbial insecticides and were applied at the recommended label rate or an experimental rate with a spray volume of ~5 gal/acre. Ambient weather conditions were recorded during applications and up to 28 days following applications. The relative humidity (68%-95%), temperature (19.5-38.2 deg. C), mean wind speed at application (0.9 -5.1 mph; 0.4-2.3 m/sec), total solar radiation (203.5-250.8 Watts/sq. m), rainfall up to day 3 (0.02″-2.31″; 0.5 mm-58.7 mm) and total rainfall at 28 days (5.0″-11.4″; 127.5 mm-289.6 mm) were measured. From the relative humidity data the delta T statistic was calculated. The value of delta T allows for the estimation of the evaporation time of an insecticide droplet and may have a significant impact for low volume applications where the droplet sizes are much smaller than high volume applications. Ideally, the value of delta T should be between 2-8. Values lower than 2 and between 8-10 indicate marginal spraying conditions. Values higher than 10 indicate conditions unsuitable for spraying. The delta T value at application in these studies ranged from 1.0-1.8. Efficacy of each application was assessed by sampling populations of both adults and nymphs in treated plots compared with untreated control plots on days: 3, 7, 14, 21, and 28 in a commercial citrus grove. Unbaited yellow sticky cards and tap counts onto white cards from multiple branches were used to determine the numbers of adults. Populations of nymphs were estimated by examination of individual flush terminals using a ranking scale. Regression analysis was used to determine if there was a relationship between the meteorological conditions measured during the trials and observed mortality of the psyllid nymphs and adults. The efficacy data for day three was compared to the above canopy wind speed at application. There was a significant positive correlation, indicating that the most effective applications of residual insecticides (organophosphates and pyrethroids) occurred at lower wind speeds but not for insecticides from other classes. No correlation with the value of delta T and efficacy was shown for all insecticides in all classes tested. However, applications were made during conditions within the recommended ranges for delta T. The maximum daily temperature for the first three days was positively correlated with increasing efficacy for the residual insecticides tested but not for other classes. The cumulative solar radiation to day 21 post-application was negatively correlated with efficacy for the residual insecticides. There was no correlation between cumulative rainfall to day three and efficacy for all insecticides tested.
This project is focused on 1) refinement of sampling methods, 2) testing the influence of adult density and shoot infestation on precision of estimated means and distribution of population within blocks, and 3) evaluation of methods for assessing psyllid density, shoot density, and infestation rates and their integration into a user friendly system accessible to consultants and managers. We have made significant progress on all three objectives 1) Comparisons of stem tap sampling, sticky traps and sweep nets in commercial citrus were published in a peer reviewed EDIS document. Data indicated that although all methods detect adult psyllids, the stem tap method is most rapid, works under either dry or wet conditions, and has proven to be reliable and consistent. A little more than 100 tap samples would be necessary to detect with confidence 15 psyllids with 75% precision, a reasonable threshold during the growing season when trees are producing new growth. We recommend 100 samples per block divided into 10 stops, five along the perimeter where psyllids tend to congregate, and five inside the block. This scheme could lead to a decision to spray only the block perimeter if necessary. Ten tap samples should be taken at each stop, one per tree. Then 10 young shoots, each containing ‘feather flush’ should be examined with a hand lens to determine if they are infested with psyllids. The search is terminated if 10 young shoots cannot be found after examining 20 trees. We are now comparing stem tap sampling with vacuum sampling in commercial citrus. The vacuum sampler is made from a leaf blower and collects many psyllids even at low populations. A single strike captured an average of about twice what a single tap sample would catch and the two samples were significantly correlated. 2) A three year study comparing the stem tap sampling and sticky traps under different levels of psyllid infestation in commercial citrus was completed. These and other data collected on comparisons of stem tap and sweep net sampling are being analyzed using regression and bootstrapping procedures. We are using precision levels of 0.25 and 0.01 SEM:mean in order to determine the number of samples required using these methods for routine monitoring and analytical modeling respectively. 3) Methods to monitor psyllids using tap sampling method and flush examination along with data sheets to record data have been posted at our website: swfrec.ifas.ufl.edu/entlab. A pest scouting workshop and citrus field day in collaboration with Hendry county extension were conducted during this quarter and appropriate sampling methods promoted to 125 participants. So far, more than 4000 tap sampling kits have been distributed to clientele through workshops conducted at SWFREC and IFAS extension. This method has been widely adopted by the citrus industry. More than 75% growers in SW Florida value tap sampling in their decision to manage psyllids along with flush examination. The success of the tap sample, is also illustrated by its adoption by APHIS and DPI CHRP to monitor 6,000 blocks of citrus in Florida every 3 weeks. Tap sampling method was also used to evaluate several experimental and recommended insecticides at SWFREC and large scale studies in commercial citrus designed to control psyllids using insecticides, horticultural oils and nutritionals. Arevalo, A. H, J. A. Qureshi and P. A. Stansly. 2011. Sampling Asian citrus psyllid (ACP) in Florida citrus groves. EDIS, http://edis.ifas.ufl.edu/in867.
The results analyzed from the 2010 field season indicate that application of sachets of methyl salicylate (MeSA) in the field plots did not significantly increase population densities of natural enemies of Asian citrus psyllid (ACP) compared with untreated plots in the large scale experiment that was conducted in groves with various levels of ACP management. In addition, psyllid populations were not different between MeSA-treated plots and untreated plots. In all of the grove types tested (unmanaged, minimally managed and intensively managed), psyllid populations were low (< 1.5 psyllids/trap/14 days). These results were different from our initial investigation in 2009, which indicated that natural enemies were higher in MeSA-treated plots. However, in that year, psyllid populations in that grove were much higher than in the groves studied in 2010. In 2009 an average of > 10 psyllid adults were captured per week in control plots whereas ~2 psyllids were captured/week in MeSA-treated plots. Also in 2009 we saw an increase in natural enemies, particularly coccinellid beetles, in MeSA-treated plots as compared with control plots. We hypothesize that the low psyllid numbers overall in 2010 could account for the lack of effect of MeSA treatment. If natural enemies were initially attracted to the plots, the lack of psyllid prey may have caused them to leave the plots in search of resources elsewhere. One recent study in strawberries indicated no increase or limited increase in natural enemies in MeSA-treated plots and no significant decrease in pest populations (Lee, J. C. 2010. Environ. Entomol. 39:653-660). It is also possible that insecticide use affected our findings in 2010. Laboratory bioassays to test the effect of MeSA on the behavior of the Asian citrus psyllid adults were conducted. In a two-choice laboratory olfactometer, adult psyllids were repelled by MeSA at the dosage tested as compared with a clean air control. We are starting studies to see if foliar applications of MeSA on citrus plants reduces the number of psyllids settling on plants compared with untreated plants. In conclusion, MeSA treatment in citrus had mixed results with respect to attraction of natural enemies and reducing psyllid populations in citrus in Florida. MeSA may have an effect in situations where psyllid populations were sufficiently high at the onset of the tests. The repellent effect observed may help reduce psyllid populations and needs further study. If MeSA reduces psyllid establishment on plants and inhibits feeding, this effect may reduce the inoculation of Candidatus liberibacter asiaticus and the incidence of citrus greening disease.
For this project, we have been investigating whether female Asian citrus psyllid (ACP) attract males with a pheromone. Laboratory olfactometer and field studies were conducted to examine the behavioral responses of male and female ACP to their cuticular extracts with a goal of identifying a female-produced sex pheromone. In laboratory experiments, more male ACP were attracted to the odor of 1, 5, or 10 ACP female cuticular extract equivalent units than clean air suggesting that female ACP produce pheromone to attract males. The results were confirmed in field studies in which clear or yellow traps baited with 10 female cuticular extract equivalent units attracted more males than the clear traps baited with male cuticular extract or unbaited traps. Furthermore, clear traps baited with 5 or 10 male or female cuticular extract equivalent units attracted more ACP than unbaited (control) traps. However, catch of psyllids on yellow sticky traps was not increased by baiting them with the psyllid cuticular extract. Collectively these investigations indicate that the extract from female ACP adult cuticle attracted male ACP in laboratory and field bioassays suggesting that female ACP produces a pheromone to attract males. Field bioassays with whole body male and female ACP cuticular extracts suggested that a constituent of the ACP cuticular hydrocarbons serves an attractant. In order to determine the specific chemicals responsible for the behavioral effects observed with psyllid cuticular extracts, chemicals analyses of these extracts were performed to determine whether differences in profiles exist between male and female extracts. Males and females were analyzed separately. There were unique chemicals associated with male and female cuticular hydrocarbon extracts. A greater amount of Dodecanoic acid was specifically identified from the female cuticular extract. In laboratory experiments, synthetic dodecanoic acid attracted significantly more male ACP than clean air. However, field experiments with dodecanoic acid have not yet generated conclusive results for its attractiveness to ACP males. In collaboration with chemists, we have modified our chemical analysis techniques for more precise identification of chemicals of male and female cuticular extracts using 10X traps. Preliminary results with modified techniques yielded more precise differences in chemical profiles between male and female psyllids. More bioassays and field experiments are in progress with newly identified chemicals.
The goal of this project was to determine if infection by Candidatus Liberibacter asiaticus (Las) affects the response of Asian citrus psyllid (ACP) to its citrus host plants. In a two-choice laboratory olfactometer experiment, more ACP were attracted to volatile chambers containing Las-infected citrus plants than chambers containing uninfected citrus plants. In settling experiments, Las-infected plants were more attractive to ACP adults than uninfected plants initially; however, psyllids subsequently dispersed to uninfected plants as their final settling point rather than infected plants. Settling experiments with Las-infected and uninfected plants under complete darkness produced similar results to experiments conducted under light conditions. Both Las-infected and uninfected psyllids exhibited similar behavioral responses to Las-infected and uninfected plants in olfactometer and settling assays. Volatiles were collected from citrus plants that were either uninfected (control) or infected with Las. The volatile profiles of these plants were analyzed using a machine-learning algorithm called ‘Random Forests’. This is a data-mining technique which allowed for the selection of the most appropriate predictor volatiles of observed ACP behavior and provided probabilities for classification of each plant as infected or uninfected based on volatiles alone. This analysis effectively divided the sampled plants into two groups, supporting a volatile basis for discrimination between infected and uninfected plants by Asian citrus psyllid. Methyl salicylate and methyl anthranilate were selected as the major predictor variables for the classification of the plant infection treatments. There was significantly more methyl salicylate (MS) and less methyl anthranilate (MA) in Las-infected plants than uninfected plants. Methyl salicylate was found to repel psyllids in laboratory olfactometer experiments at a 100 mg dosage. There was no effect of MA on the behavior of psyllids. In addition to investigating ACP response to plant odors and whether it changes due to Las infection, we investigated the hypothesis that infection may influence plant nutritional status and that this may affect psyllid host choice behavior. Nutritional analysis revealed that HLB-infected plants in our experiments were deficient in zinc, iron, nitrogen and phosphorus and produced more potassium and boron than uninfected plants. Experiments investigating how nutritional status of plants due to infection affects psyllid behavior are underway as part of our ongoing and future studies. Collectively, our results indicate that ACP host seeking behavior is modified by changes plant volatile release due to infection with Las, which alters headspace volatile release and nutrient profiles of infected plants and compared with uninfected controls.
Insecticides are currently the basis of Asian citrus psyllid (ACP) management programs and the number of annual insecticide applications has increased significantly. A two-year study (2009-2010) was conducted to develop baseline studies on levels of insecticide resistance among five geographically discrete populations of ACP across Florida. In 2009, one or more field population of ACP were less susceptable to fenpropathrin, imidacloprid, malathion and thiamethoxam compared to a laboratory reared susceptible population. In 2010, susceptibilities of field populations were compared with the laboratory susceptible population. In general, the susceptibility of ACP from field collected populations was lower than that of the laboratory susceptible population for most of the insecticides tested. In addition, immature ACP from four field populations were determined to have decreased susceptibility levels to the majority of insecticides tested. Increased levels of insecticide resistance among field populations was positively correlated with increased levels of three detoxifying enzymes: general esterases, glutathione S-transferases and cytochrome P450 monooxygenases. In order to better understand the genetic mechanism underlying increased levels of cytochrome P450 monooxygenases in insecticide resistant populations, we investigated the expression levels of family 4 cytochrome P450 (CYP4) genes in adult ACP when exposed to varying levels of imidacloprid. Five novel CYP4 genes (CYP4C67, CYP4DA1, CYP4C68, CYP4DB1 and CYP4G70) were identified from adult ACP. Expression of all five CYP4 genes was induced by exposure of ACP to imidacloprid suggesting their involvement in metabolism of this toxin. In addition, four of the five CYP4 genes were expressed at significantly higher levels in uninfected than Las-infected male ACP, whereas only one was expressed at significantly higher levels in uninfected than Las-infected females. These results suggest that levels of cytochrome P450 monooxygenases in ACP may be linked to expression levels of these CYP4 genes. Previously, we reported that Candidatus Liberibacter asiaticus (Las)-infected ACP are characterized by lower levels of cytochrome P450 monooxygenases than uninfected counterparts. In addition, expression of some of these CYP4 genes appears to be sex-specific. Higher expression of the five CYP4 genes occurred in nymphs than adults, which is congruent with previous results indicating higher levels of cytochrome P450 monooxygenases in nymphs than adults. These five CYP4 genes may be promising candidates for RNA-interference to silence over-expression of genes associated with insecticide resistance in ACP. These newly identified genes may also serve as DNA-based screening markers for cytochrome P450-mediated insecticide resistance in field populations of ACP.
The goal of this project is to evaluate existing and known insect repellents to determine if they can be useful tools for Asian Citrus Psyllid (ACP) management. Also, we are focusing our investigations on chemicals that would otherwise be safe to the environment and not harm beneficial insects. The objectives include examination of repellent and toxicological properties of selected botanical chemicals against ACP. We will plan to evaluate 30 plant produced chemicals that are known insect repellents for their repellent and insecticidal activities against ACP with an intent of identifying effective tools for ACP management. We have selected and purchased the candidate compounds and standardized a protocol for evaluation of their effects on ACP behavior. For behavioral bioassays, we are using a customized T-Maze laboratory olfactometer. The olfactometer consists of a 30 cm glass tube that is bifurcated into two equal halves with a Teflon strip forming a T-maze. Each half serves as an arm of the olfactometer enabling the ACP to make a choice between two potential odor fields. The olfactometer arms are connected to odor sources placed in solid-phase micro-extraction chambers (ARS, Gainesville, FL) through Teflon-glass tube connectors. The samples are diluted in appropriate solvent and subsequently pipetted onto a 5 cm Richmond cotton wick, which serves as the release device. Each chemical is evaluated individually and tested with at least 4 dilutions (dosages) on a log scale to determine optimum release rate. The control treatment consists of a cotton wick impregnated with solvent only. The olfactometer is housed within a temperature-controlled room and positioned vertically under a fluorescent 900 lux light bulb fixed in a fiber board box for uniform light diffusion. This position takes advantage of the negative geotactic (inclination to move up) and positive phototactic (attraction to light) response of ACP. Preliminary experiments with some tested chemicals indicated that citronellol, a sesquiterpenoid from lemon grass oil, repelled psyllids in the laboratory experiments. Behavioral bioassays with more botanical chemicals are in progress. To evaluate insecticide contact activity of these chemicals, we have obtained an automatic microapplicator that is being used to apply known and minute quantities of tested chemicals onto psyllids. Seven serial dilutions for each test chemical are prepared by dissolving the test chemical in acetone or absolute alcohol. Thereafter, 0.4 ‘l of each serial dilution of test chemical or a solvent only (control) treatment is applied to the dorsal mesothorax of adult psyllids. Treated psyllids are transferred to Petri dishes containing citrus leaf discs placed on a solidified agar beds. Mortality of ACP is scored 48 hr after exposure to treatments. Data are analyzed using standard probit analysis. Currently, these toxicological investigations are underway.
Leaf residue toxicity studies. The objective of this experiment has been to determine the residual efficacy of low volume and high volume insecticide applications on citrus leaves. Fenopropathrin (16 oz/acre), phosmet (1.5 lb/acre) and imidacloprid (15 oz/acre) were applied to citrus either as a low volume (LV) at 12 gpa or a high volume (HV at 200 gpa) application. For the fenpropathrin and imidicloprid treatments, 2% V/V of 435 crop oil was added and for the phosmet treatment LI-700 was added to adjust the pH of the solution to the recommended range. At 4 and 8 days post-application, leaves were removed from the plots and a leaf disc mortality bioassay was performed in Petri dishes. Approximately 15 adult Asian citrus psyllids were placed in the dishes with leaf discs of either the treated leaves or untreated control leaves. Adult mortality was assessed at 24 h and 48 h post exposure. Four days after treatments were applied, the 24 h exposure mortality for HV treatments was 100% for fenpropathrin, 84% for phosmet and 61% for imidicloprid. The only treatment with any mortality for LV applications was phosmet at 2.2%. After 48 hrs of exposure, all the HV treatments had >90% mortality. Mortality in all the LV treatments was <10%. Leaves removed from the field at day 8 caused much lower mortality in HV applications than at day 4. After 24 h of exposure exposure the mortality for fenpropathrin was 79%, phosmet was 14% and imidicloprid was 16%. Interestingly, the LV mortality at day 8 was somewhat higher than at day 4 for phosmet (14%) and imidicloprid (18%). After 48 h of exposure, mortality was higher for both HV and LV treatments. Border row treatment. In these experiments our goal is to compare the reduction in psyllid populations when treating all rows of citrus grove plots versus border row only treatment. All treatments are made to plots where psyllid populations were low initially because of a previous comprehensive treatment. In a 44 acre commercial grove, plots have been sprayed with 16 oz/acre of fenpropathrin with 2% V/V 435 crop oil added as a LV application of 12 gpa. In 3 of the plots, every tree was sprayed and in another 3 plots, only the outer 2 rows of trees were sprayed. Three plots were left untreated as control plots. We have completed the first trial of this experiment and are analyzing the results. A second replication is planned for early July, a third in August. Canopy investigation. This experiment is designed to investigate the distribution of adult psyllids within the tree canopy with the goal of optimizing insecticide spray applications. Sampling of the mid and upper parts of the canopy of mature trees for psyllid adults has been initiated. To date, three fold more adult psyllid have been found in the upper canopy than at mid-canopy level.
The goal of the present project is to establish economic thresholds under different juice price scenarios that optimize returns on investment when a nutrient/SAR package is being applied in groves with moderate to high incidence of HLB. Two 3-year field experiments were initiated in two commercial orange blocks in Hendry County (southwest Florida). One of the groves is planted with ‘Earlygold’ oranges and the other with ‘Valencia’ oranges. Average HLB incidence estimated in both groves based on PCR analysis of a random sample of 160 trees is 98% in ‘Earlygold’ and 76% in ‘Valencia’. Experimental design is randomized complete block with 4 replicates and 4 treatments: (1) No insecticide, (2) Calendar applications, in order to drive vector populations close to 0, (3) nominal threshold of 0.2 psyllids per tap, and (4) nominal threshold of 0.7 psyllids per tap. Calendar applications are being applied approximately every 1 month and consist of a rotation of insecticides recommended for managing this pest. Treatment (2) has been sprayed in both blocks with carbaryl (Sevin XLR Plus ) at 0.75 gal/ac in April, spinetoram (Delegate WG) at 4.5 oz/ac in May and imidacloprid (Admire Pro) in June at 4.5 oz/acre. No sprays have been applied for treatments (3) and (4), during the last 3 months because nominal threshold populations have not been reached. Adult psyllid populations are being monitored every two weeks by tap sampling. Flushing patterns and flush infestation are being estimated by assessing the number of new shoots per tree and evaluating the proportion infested with psyllids. Effects of treatments on natural enemy populations are being evaluated by counting beneficials in tap samples, suction samples, flush observations. Additionally, exclusion studies on ACP infested flushes are being conducted in treatments (1) and (2) to evaluate the potential negative incidence of the sprays on the ACP beneficials. A branch with emerging flush is caged with a small number of adult psyllids for 3 days. Resulting eggs and 1st instar nymphs are counted and the cages replaced on half the branches. When the nymphs have reached 5th instar or are ready to emerge as adults the brances are removed and all surviving nymphs are counted. The difference in survival between caged and uncaged branches is taken as the effect of predation on the psyllid cohort. The first such study run in June indicated ACP mortality of 82.8 ‘ 4.9 % in treatment (1) and 69.1 ‘ 9.0 % in treatment (2). The greater reduction in treatment (1) may indicate greater activity of natural enemies in the absence of insecticide applications, and provide a better picture of the faunal changes that have occurred in response to treatments. Secondary pests and their natural enemies are also being studied during the growing season in the four threshold treatments. Citrus leafminer (CLM) densities are being monitored using pheromone traps. A trend toward lower CLM activity in treatment (2) has been observed although differences are not yet significant (P = 0.1024; df = 3,15; F = 2.577 for the ‘Earlygold’ block and P = 0.1018; df = 3,15; F = 2.638 for the ‘Valencia’ block). In contrast, citrus red mites showed significantly higher populations in treatment (2) compared to other treatments in the ‘Valencia’ block (P = 0.0003; df = 3,1599; F = 6.424), in concert with significantly lower populations of predatory mites (phytoseids) (P = 0.0009; df = 3,1599; F = 5.600). These results would indicate that the calendar applications had a negative effect on phytoseids, and therefore their prey, citrus red mites, increased their numbers. Further studies in the following months on these and other secondary pests will help us to elucidate the costs incurred by spraying due to disruption of biological control.
Ultra low-volume and Aerial Application of Insecticides and Horticultural Mineral to Control Asian Citrus Psyllid in Commercial Orchards. Low volume (LV) aerial and ground sprays have become an important method of application during the dormant season and at other times in SW Florida. We continue our evaluations of LV application of 435 horticultural mineral oil (HMO) which has shown promising results the last 3 years. This report documents updated results from the fifth trial begun on February 2011 in a 10.9 acre plot of ‘Valencia’ orange in Lee County that compares the efficacy of low volume spray spray of 435 horticultural spray oil (HMO) with the grower standard and an untreated control. Seven sprays of 435 oil (23Mar, 12Apr, 21Apr, 28Apr, 5May, 19May, 2June, 14June) have been completed since the last report. A grower standard of 6 oz of Actara/ac + 2gal HMO/ac was applied in 10 gpa spray mix on 2 May. On 14 June, 10fl oz/ac of abamectin 0.15 (Agri-mek) plus 2 gal HMO oil was applied in a 10-gal mix. Thus far mean psyllid populations have been below the 0.2 threshold for grower standard between 12 Apr and 20 June, whereas the oil treatment has been above threshold for 26 Apr, 9 May, 24 May, 6 June, and 20 June. There were significant differences between grower standard and oil treatments on 9 May (p = 0.06), 24 May (p = 0.04), with grower standard having less psyllids present (0.08 +/- 0.06SEM, 9 May; 0.07 +/- 0.06SEM 24May) than oil (0.25 +/- 0.06SEM 9 May; 0.25 +/- 0.06SEM). However, during June tap sampling, these significant differences disappeared (p > 0.05), and the mean psyllid counts for grower standard were 0.12 +/- 0.08SEM, 0.10 +/- 0.10SEM, and for oil (0.23 +/- 0/8SEM, 0.33 +/- 0.10SEM) on 6 June, 20 June, respectively. We added citrus leafminer assessments to this grove to determine if treatments are affective at reducing leafminer numbers. We placed pheromone traps in the grove on 24 May and have conducted one damage assessment of leaves using a modified Horsfall Barratt scale. There were significant differences between the grower standard and oil (p = 0.03) with the grower standard having less leafmining damage (0.50 +/- 0.05SEM) than the oil treated plot (0.68 +/- 0.06). All the spraying with broad-spectrum insecticides appears to be increasing incidence of various secondary pests including scale insects, mites and citrus leafminer (CLM). Furthermore, canker is an increasing problem throughout the area which has increased concern about CLM. CLM control requires precise application timing on emerging flush to be effective so there is considerable interest in aerial application. Therefore, we are evaluating aerial application of two products widely used for leafminer control, the insect growth regulator methoxyfenozide, and spinetoram, an analog of spinosyn A which is derived from actinomycete bacteria. Both products are selective with low vertebrate toxicity. The replicated trial in being conducted on an 80 acre block divided into 12 large plots in a replicated complete block design with 4 treatments and 3 replications. Pheromone traps are being used to monitor CLM populations within all plots before and after the applications which are planned for 7 July when summer flush will be optimal for maximum control.
In California, citrus nursery stock must be treated with both a systemic and foliar pesticide in order to move it within areas quarantined for the Asian citrus psyllid (ACP). The purpose of these treatments is to prevent ACP from establishing in nurseries and being moved around California when the plants are sold. Imidacloprid is one of the systemic insecticide options available to nurserymen and is the focus of our research at UC Riverside. However, there are other systemic neonicotinoids recommended by the CDFA that growers are permitted to use on their citrus before shipments leave the nursery. These insecticides include Safari (dinotefuran) and Platinum (thiamethoxam), and this report summarizes our data on these compounds. We are evaluating Platinum and Safari uptake and persistence in 2 citrus varieties, ‘Kinnow’ mandarins (1 year old) and ‘Tango’ mandarins (3 years old). Admire Pro (imidacloprid) was also included in the trial. Both varieties are budded on ‘Carrizo’ rootstock. Trees were treated with the current label rate for Platinum and Safari, and the 0.33 ml/cu ft potting media rate of Admire Pro. Within 1 week of treatment with Admire Pro, imidacloprid levels were above the 200 ppb threshold established by Mamoudou Setamou as the dose needed to kill ACP nymphs. We use this concentration to evaluate the efficacy of our treatments. Mean concentrations in both the Kinnows and Tangos were at 1800 ppb. At week 2, the concentrations had increased further. The levels in the Kinnows and Tangos were 6,000 ppb and 6,550 ppb, respectively. Clearly, the trees were well protected within 1 week of treatment. As yet, there are no data available to guide us on how much thiamethoxam (Platinum) or dinotefuran (Safari) we need to have in the trees to protect them. However, at the label rates we tested, the concentrations were in the ppm range within 1 week of treatment, suggesting that the trees would also be protected from ACP. Thiamethoxam concentrations in the Kinnows and Tangos were 1,600 ppb and 2,400 ppb, respectively, at one week, while concentrations of dinotefuran in the Kinnows and Tangos were 12,000 ppb and 8,100 ppb, respectively, at one week. The substantially higher concentrations of thiamethoxam and dinotefuran compared to imidacloprid are not surprising given their higher water solubilities. Thiamethoxam (4 g/l) is about 8-fold more water soluble than imidacloprid (0.5 g/l) and dinotefuran (40 g/l) is 80-fold more water soluble than imidacloprid. The higher water solubility will permit a more rapid uptake of insecticide into the trees; however, it could also result in a less persistent product due to more rapid depletion of soil reservoirs of insecticide. We will monitor the concentrations in these trees for 6 months to determine the longevity of residues within the trees. This information will guide future uses of these products on nursery citrus. We are continuing to monitor imidacloprid applications in a commercial nursery. By doing this, it allows us to evaluate the efficacy of treatments in citrus growing under normal production conditions, as opposed to the more controlled environment of a laboratory or greenhouse trial. We generally measure lower levels of imidacloprid in commercial citrus, although the treatments do reach the 200 ppb threshold concentration. The more frequent appearance of flush at the commercail sites results in lower titers of imidacloprid because the new tissue grows at a rate that is faster than the rate of movement of imidacloprid. This result reaffirms the importance of the foliar treatments for nursery stock that is due to leave the faciity. The foliar treatments will protect the citrus until the imidacloprid establishes at threshold concentrations.
The agreement between CRDF and ARS is now in place for this project. This initial report covers the period from the agreement start date of 1 May through 30 June 2011. No expenditures have been charged to this project to date. Field work has continued uninterrupted this year with 3 applications of SPLAT-CLM made at two locations: 2 applications to 90 acres in a grapefruit grove in St. Lucie county and 1 application to 82 acres in an orange grove in Charlotte county. A second application will be made in Charlotte county in early July. Complementary experiments were installed at the two sites to determine the potential for reducing the cost of SPLAT-CLM applications by leaving untreated beds (gaps). End of year analysis of results of various gap treatments will attempt to identify coverage patterns that optimize mating disruption and amount of product applied. The prototype applicator has been improved by the addition of two cylindrical hoppers capable of holding sufficient SPLAT-CLM to treat 50 acres at a time. GPS telemetry and software-driven pump speed contributed to a very high degree of precision in terms of the amount of product applied per acre. Precise application is particularly important given the relatively high cost of SPLAT-CLM. The longevity of a single application continues to be studied to determine the frequency of application required to maintain effective control throughout the year. We will continue to focus on reducing the cost of mating disruption to control CLM and associated citrus canker disease by identifying the most cost-effective coverage pattern and frequency of application. Craig Keathley has been selected and has accepted a position as postdoctoral research entomologist at USHRL, Ft. Pierce. He will defend his thesis in late August and begin his duties related to this project in early September. Craig will receive his PhD from the University of Kentucky’s Entomology Department where he studied under Dr. Daniel Potter. In addition to his academic qualifications, the soon-to-be Dr. Keathley worked as a vegetable crop pest control adviser in California prior to his doctoral studies at UK. We are excited to have Craig join our team and look forward to his contributions to this effort.
We have completed a confirmation test to demonstrate control of bean thrips by fumigation with Vapormate. More than 30,000 adult bean thrips were placed into the navels of navel oranges (10-15 per orange) and stored at 41F overnight to drive the thrips deep into the navel. The next day, the oranges were packed into boxes and loaded into a marine container with filler fruit to make 8 full pallets of packed orange boxes. Following the 1 hour fumigation, the infested oranges were retrieved and thrips mortality was determined to be 100%. Fruit quality was also assessed on export quality fruit following fumigation with Vapormate. There were no significant effects on fruit quality. We have also developed a dose mortality curve through small scale tests in the laboratory and determine the concentration of Vapormate required to achieve Probit 9 mortality at 41, 50 and 59F. We are preparing a manuscript on this work for publication in the Journal of Economic Entomology.
This project was designed to examine the potential disease control of citrus huanglongbing (HLB) by interplanting citrus with guava. In Vietnam guava has been shown to be an effective deterrent to HLB, slowing the disease and keeping plantings alive for up to 15 years that normally succumb in 2-3 year. For all plots and experiments, Guava trees, (Vietnamese white cultivar) were propagated and grown to appropriate size requiring ~1 year. Both nursery and field citrus trees are assayed for HLB every 60 days, and have been assayed multiple times. Psyllid populations are monitored continuously every 2 weeks to document repulsion of the vector. Results: Guava vs no guava nurseries: Two nursery sites, a guava protected citrus nursery versus an unprotected nursery, have were established with disease free, PCR-negative citrus trees (2 sweet orange and 1 grapefruit cultivars) in June 2009 and were located in the protected and unprotected plots. The guava trees were grown to appropriate size as indicated in Vietnam prior to outplanintg. To date HLB appears to be progressing more slowly in nursery plots interplanted with guava than in non interplanted plots. The freezes discussed below did not adversely affect these nursery plots. Citrus/guava interplantings: 2 commercial plantings with multiple replications were established but due to freezes and property sales these plantings are no longer viable. A third trial planting was established at the USHRL Picos Farm in Fort Pierce. The Picos plot was interplanted with citrus in August 2009. Severe frosts during 2008/2009 and again during 2009/2010 winters affected the USHRL plots and caused a delay in the experiment. A final hard freeze during the 2010/2011 season killed most of the guava trees. Data analysis to date indicates no differences were observed among treatments, i.e., guava interplanted vs. non-interplanted plots prior to the final demise of the plots. Our interpretation is that Florida is actually a subtropical environment, prone to intermittent freezes and cool or cold temperatures. Whereas, Vietnam and Indonesia, where the guava effect seems to work, are truly tropical without such broad temperature swings. After freezes it takes a considerable time to either replant guava or for the freeze damage guava to recover. Even during cool weather guava trees are very sensitive and do not continue to flourish and grow. It is the new flush of guava which appears to be the best at producing ACP repellent volatiles. Cool or freezing temperatures inhibits volatile production and thus the citrus crop is left unprotected from ACP. While guava not be a viable deterrent as an intercrop, it still may be possible to identify individual volatiles from guava that might be useful under field applications as chemical applications. Moving forward: We have switched direction slightly to investigate other more temperate Myrtaceous plant species that are more cold tolerant and might be useful as intercrops. Research continues using a Y-tube olfactometer to continue to investigate guava volatiles as repellents of the psyllid as well as to investigate the feasibility of other Myrtaceous plants. To date we have not bee able to determine any differences in y-tube olfactometer experiments
We completed a trial in Ventura County where we monitored the uptake of imidacloprid in lemons applied at 3 timings during the season. The uptake of imidacloprid (determined by whether the 200 ppb target threshold for ACP control was reached) was not good at this site. The reason for the poor uptake was likely due to a 3 week interval between irrigations, and heavy soil conditions. The soil texture was determined at this site to be 25% clay and an organic matter content of 6%. On May 11, 2011, we retreated trees that had been treated in 2010 with a further application of imidacloprid. Thus far, we are not detecting imidacloprid in trees that received 2 successive years of imidacloprid treatments. We have started a new trial on mandarins in Kern County. We plan to put on 4 imidacloprid treatments leading up to the Fall flush to determine how effective imidacloprid will be at protecting the young leaf tissue. The trial is being conducted in 2 blocks that are under different irrigation systems (drip v fanjet). The first treatment timing was administered on June 9 following the removal of the nets from the trees, and we have begun our residue analyis. We are working with Terry Nelson of Oxnard Pest Control to establish additional sites in Ventura County to evaluate imidacloprid uptake. Our goal is to select sites with lighter soils where the irrigation is more frequent. In conjunction with the imidacloprid treatments at the Ventura site, we are also evaluating thiamethoxam uptake. We have not detected thiamethoxam at 2 weeks after treatments were applied. In August, we plan to apply further thiamethoxam treatments to the grapefruits at Hemet, in an effort to determine what is happening to the insecticide. We have applied clothianidin as a soil treatment and trunk spray to navel oranges at Lindcove Research and Extension Center. Working with Pat Clay of Valent, we were able to get Belay 2.13 SC and an adjuvant for the trunk spray work. The method of application appears to be relatively easy and would be a good option for some growers. We have no data for clothianidin on citrus so this is an important study for the citrus industry. The first samples were taken on June 15 (1 week after treatments) and no clothianidin was detected in either set of treated trees. The results of the Spring 2010 nectar collections have been summarized in a report that has been submitted to the CA-DPR and US-EPA. Imidacloprid did not accumulate in the nectar sampled from trees treated in successive years with the 1X rate of application. Residues were higher in trees treated in the Fall versus those treated in the Spring, but the levels were still well below the No Effect Level of 20 ppb set by Bayer CropScience. In Spring 2011, further nectar samples were collected from field sites where imidacloprid treatments had been applied. In all, 105 samples were collected from sites that differed in soil type and in the number of successive years that imidacloprid had been used. The samples will be analyzed by Dr Bill Leimkuehler of Bayer CropScience.
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