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Research Project: Production and Disease and Pest Management of Horticultural Crops

Location: Southern Horticultural Research

2015 Annual Report

Objective 1: Develop integrated strategies to control invasive diseases and pests within the context of small fruit production systems of the Gulf Coast. Sub-objectives: 1.1: Determine the importance of wild fruit hosts to the ecology and life history traits of Spotted-wing Drosophila (SWD) and other vinegar fly pests of fruit crops of the U.S. Gulf Coast, with an emphasis on fly population dynamics in surrounding landscapes. 1.2: Develop and evaluate Integrated Pest Management (IPM) strategies involving selective chemical application. 1.3: Determine pathogen lifecycle events and spread patterns of bacterial leaf scorch, a new and emerging disease of blueberries in the Gulf South. 1.4: Develop disease screening assays using traditional and molecular screening techniques to identify disease resistant small fruit germplasm and characterize relevant host/pathogen relationships, the influence of cultural practices, and virulence levels of pathogens. 1.5: Develop disease control protocols based on cultural practices of removing rosette infected primocanes, which are a source of fungal inoculum, to reduce rosette disease severity in erect blackberry cultivars. Objective 2: Develop disease and pest control strategies that can be readily integrated with existing production practices used in container-grown ornamental plant nursery systems. Sub-objectives: 2.1: Develop a three-step ‘push-pull’ management strategy for protecting vulnerable nursery tree stock from ambrosia beetles. 2.2: Examine the effect of binding and leaching potential of soil-incorporated insecticides in alternative and standard soilless substrates in container-grown ornamental plants. 2.3: Determine optimal timing of disinfestant to restrict pathogen dispersal through irrigation water and limit plant disease. 2.4: Develop a comprehensive preventive and reactive disease management strategy to control Pseudomonas, Colletotrichum, and Rhizoctonia in plant propagation facilities. 2.5: Develop an integrated disease management strategy to control Leyland cypress blight in ornamental plant nursery production. 2.6: Identify changes in spray patterns across 100 foot blocks of container-grown plants using commercial sprayer equipment that correlate with reduction in disease intensity. Objective 3: Develop and improve pollination practices on berry and vegetable farms along the Gulf Coast and increase capability to use native bees.

Develop an updated pest management program to control the spotted-wing Drosophila fly from damaging fruits and vegetables. Develop cultural and chemical controls and tolerant cultivars of several small fruit diseases, with emphasis on Phytophthora root rot, a serious existing disease, and Xylella bacterial leaf scorch, a new disease of blueberry. Identify habitat sources of ambrosia beetle, and characterize repellant and attractant strategies that prevent ambrosia beetle movement into ornamental plant nurseries. Develop updated plant disease management practices to control existing and new pathogens in propagation, to time disinfestant treatments that prevent spread of Phytophthora in irrigation water, and to produce a risk-based fungicide timing model to control Passalora blight of Leyland cypress in the nursery. Nesting habitat for native pollinators will be promoted to expand bee management practices that are critical for achieving profitable fruit and vegetable yields.

Progress Report
In 2015, a small fruit entomology group developed effective population control of invasive spotted-wing Drosophila fly (SWD) in berry crops. ARS researchers identified ethanol as an ecological constraint on SWD distribution, rotting berries or waste areas would therefore make poor breeding sites. Costly, labor-intensive crop cleanup may therefore be unnecessary for controlling SWD. Researchers in Poplarville, MS are also experimenting with sugar-alcohols, insect growth regulators, and their new formulations, as possible chemical controls for SWD. The growth regulator, Lufenuron, fed to SWD adults and immatures killed eggs and larvae at concentrations lower than 0.1 ppm. Since eggs fail to hatch, berry damage could be mitigated and shelf life of berries extended when higher doses of Lufenuron are applied. In 2015, a small fruit pathologist determined pathogen lifecycle events and spread patterns of bacterial leaf scorch, a new and emerging disease of blueberries in the Gulf South. A second year of data confirmed the first year results. Infection by the bacterial leaf scorch pathogen, Xylella fastidiosa, was correlated with lower yield in a rabbiteye blueberry orchard in Louisiana. Significant differences between infected and non-infected plants were detected for both total yield and average berry weight. Additional X. fastidiosa isolates were detected by enzyme-linked immunosorbent assay (ELISA) and/or real-time polymerase chain reaction (PCR) in rabbiteye blueberry plants from orchards in Louisiana and Mississippi that have experienced plant decline and/or death. Disease screening assays were developed using traditional and molecular screening techniques to identify Phytophthora disease resistant small fruit germplasm and characterize relevant host/pathogen relationships, the influence of cultural practices, and virulence levels of pathogens. Additional isolates of the root rot pathogen, Phytophthora cinnamomi, were collected from soil samples near symptomatic blueberry plants in the Gulf South and identified using morphological and molecular techniques, and their virulence determined by growing root rot susceptible blueberry cultivars in soil infested with each isolate. Disease control protocols were developed based on cultural practices of removing rosette infected primocanes, which are a source of fungal inoculum, to reduce rosette disease severity in erect blackberry cultivars. Mowing and disease control treatments were applied to two rosette susceptible blackberry cultivars established in replicated plots at Thad Cochran Southern Horticultural Laboratory in Poplarville, MS. These plants did not have any rosette disease symptoms in 2015 nor did they produce any fruit. This result was expected since these are only one-year-old plants. In 2015, an entomology group of ARS researchers in Poplarville, MS and Wooster, OH and University Cooperators at Virginia State University have developed a method for monitoring exotic ambrosia beetles in ornamental crops. Large numbers of female ambrosia beetles can now be sampled by attracting them to trunk sections from discarded trees (bolts) laced with ethanol, the “pull” component of a “push-pull strategy’ for control. In 2015, ornamental plant pathology research involved a field trial to evaluate the droplet output pattern of a sprayer to regress spray coverage and disease control intensity. The equation will be used to critically evaluate efficacy of spray coverage patterns over 50 foot distances of blocks of container-grown azaleas. A manuscript was published this year that documents that natural challenges exist in recovering highly virulent Phytophthora species from the larger Phytophthora species population recycling irrigation reservoirs, and resulted in a complete experimental design change in determining optimal timing of disinfestant in treating irrigation water. Mini- ponds with manipulated water flows are being installed to test temporal spread pattern of Phytophthora species into recycling ponds, in conjunction disinfectant rate trials are being run. Disinfection rates studies using P. nicotianae, a common pathogen of ornamental plants, are ongoing. Complete set up of greenhouse irrigation systems are being done to run propagation disease control studies, which will be started once technical support is provided. All equipment has been amassed and sampling paraphernalia modified but no other progress has been made on the temporal monitoring to disease components of Passalora blight on Leyland Cypress, due to lack of technical support. In 2015, a group of ARS and MSU entomologists conducted studies to survey pesticide (including neonicotinoids) concentrations in honey bee hives and assess corresponding colony health in apiaries across intensive southern row-crops production areas (i.e. comprehensive agricultural areas with corn, cotton, rice, wheat and soybean as primary crops where neonicotinoid use is pronounced) and areas where exposure to neonicotinoids or other pesticides is less likely (i.e. CRP or pasture/prairie land). Our goal is to correlate hive health with exposure levels to pesticides, incidence of varroa mites, and availability of food sources. Studies targeting honey bee hive health is being conducted in cooperation with various University scientists in Arkansas and Tennessee. The crop composition has been determined in a minimum of a 3 mile radius from the center of each study area. At each apiary, hives were established from packaged bees in the spring of 2014. Hives now total ca. 40 per apiary. In 2014, at each location, samples of adult bees, drone pupae, wax, honey, and bee bread will be collected from all hives. Using the USDA AMS Chemical Laboratory in Gastonia, NC., we detected in-hive concentrations of multiple insecticides, miticides, and especially fungicides, but no neonicotinoids were detected in any samples from the Arkansas apiaries. However, we did detect neonicotinoids in the hive samples from one apiary in Tennessee. In addition, complete assessment of colony growth and health parameters was performed on all hives. This included hive weights and counts of adult honey bees, brood, food stores, and other colony health parameters. We did not see any direct or acute effects on honey bee health form hives located in comprehensive agricultural areas nor those exposed to certain pesticides. These efforts are continuing in the summer of 2015, with the addition of more apiaries and 2 added post-docs that will focus on determining sublethal effects from pesticide exposure. We are also examining the interaction of coumaphos, alone and in combination with, neonicotinoids. Coumaphos is a miticide used by beekeepers to control varroa mites. However, it has been shown to have a negative acute effect on bee health, and therefore is not recommended for use. From our 2014 in-hive pesticide residue samples, we found coumaphos in many samples in many hives, but at very low levels (ca. acute LD1-5). Therefore, in 2015 we have designed laboratory and whole hive experiments to evaluate the effect long-term exposure of honey bees to low levels of coumaphos may have on health both alone and in combinations with certain neonicotinoids. To date, over 60 honey bee hives are now located at the Thad Cochran Southern Horticultural Laboratory, with over 20 being used for these experiments. Results will shed much light on whether or not this common pesticide residue is affecting honey bee health and should steps be taken to ensure clean beekeeping equipment is utilized, including coumaphos-free wax.

1. A straightforward cultural control tactic for saving ornamental trees from ambrosia beetle attack. Ambrosia beetles are a threat to both ornamental and native trees because it takes only a single female beetle to infect plants with deadly fungal pathogens that clog water-conducting tissues causing entire trees to lose their leaves and die. As part of efforts to develop a push-pull method of tree protection, ARS researchers at the Thad Cochran Southern Horticultural Laboratory in Poplarville, MS and ARS cooperators in Wooster, OH used linear transects containing beetle traps at varying distances from the forest edge to assess beetle dispersal distances. These field data revealed that ambrosia beetles exhibited an unexpectedly short flight range, less than 50 m from the forest into the open nursery, beyond which trees have a >95% chance of escaping infestation, thereby making costly insecticide applications unnecessary.

2. Cleanliness can be a major barrier preventing binucelate Rhizoctonia, cause of web blight, from contaminating pathogen-free azalea stems in propagation. In the southern and southeastern U.S., azaleas have been propagated for years in hoop houses with polyethylene ground fabric or gravel floors. Annually, a few healthy looking azalea stem cuttings can carry binucleate Rhizoctonia's that spread and colonize large numbers of the next year's azalea crop of rooted cuttings and the fabric and gravel floors in propagation houses. An ARS scientist with the Thad Cochran Southern Horticultural Laboratory in Poplarville, MS developed a hot water submergence technique that produces Rhizoctonia-free cuttings. The same scientist showed the pathogen persists in floor layers of propagation houses where pathogen-free cuttings will be housed, thus allow cuttings to become contaminated again. Contamination of the next year's crop can be prevented by using a two-step sanitation approach between crops when propagation houses are empty. Step one is to remove the pathogen's food base of organic matter by removing leaves and pine bark growing media then washing the floor to remove fine bark media particles. Step two is eliminating the pathogen by spraying the floor with a disinfestant followed by exposing the clean floor to several weeks of the sun's UV radiation. The two-step approach will allow propagation of Rhizoctonia-free azaleas, something that previously has not been possible.

Review Publications
Zhang, H., Richardson, P.A., Belayneh, B.E., Ristvey, A., Lea-Cox, J., Copes, W.E., Hong, C. 2015. Comparative analysis of water quality between runoff entrance and middle of recycling irrigation reservoirs. Water. 7:3861-3877; doi:10.3390/w7073861. 2015.
Copes, W.E. 2015. Spread potential of binucleate Rhizoctonia from nursery propagation floors to trays containing azalea stem cuttings and sanitary control options. Plant Disease. 99:842-847.
Copes, W.E. 2015. Weather-Based forecasting of Rhizoctonia web blight development on container-grown azalea. Plant Disease. 99:100-105.
Landolt, P.J., Cha, D.H., Werle, C.T., Adamczyk Jr, J.J., Meagher Jr, R.L., Gilbride, R., Clepper, T., Reed, H.C., Teal, P.E., Sampson, B.J. 2014. Polistes spp. (Hymenoptera: Vespidae) orientation to wine and vinegar. Florida Entomologist. 97(4):1620-1630.
Cha, D.H., Adams, T., Werle, C.T., Sampson, B.J., Adamczyk Jr, J.J., Rogg, H., Landolt, P.J. 2013. A four-component synthetic attractant for Drosophila suzukii (Diptera: Drosophilidae) isolated from fermented bait headspace. Pest Management Science. 70:324-331.
Stringer, S.J., Draper, A., Marshall-Shaw, D.A., Sampson, B.J., Adamczyk Jr, J.J. 2015. 'Bluesfest' Rabbiteye Blueberry. HortScience. 50:934-935.
Werle, C.T., Chong, J., Sampson, B.J., Reding, M.E., Adamczyk Jr, J.J. 2015. Seasonal and spatial dispersal patterns of ambrosia beetles (Coleoptera: curculionidae) from forest habitats into production nurseries. Florida Entomologist. 98: 884-891.