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

Location: Southern Horticultural Research

2014 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 FY 2014 a small fruit entomology group established and are maintaining 240 cultures of Drosophila suzukii (spotted-wing drosophila, SWD) and 60 to 80 colonies of wild type Drosophila melanogaster. Some of the D. melanogaster cultures poorly express or lack the alcohol dehydrogenase, potentially making SWD susceptible to ethanol. Ethanol may be useful as an environmentally sound biopesticidal product. Progress was made constructing arrays of plastic chambers equipped with loading vials that permit exposure of adult and immature SWD in vivo to natural products with repellent and toxic properties. These bioassay arrays are being used to detect antibioses against SWD oviposition among elite accessions of small fruit germplasm. In FY 2014, a small fruit pathologist correlated infection by the bacterial leaf scorch pathogen, Xylella fastidiosa, with lower fruit yield in a rabbiteye blueberry orchard in Louisiana. X. fastidiosa was detected by ELISA and/or real-time PCR (Polymerase Chain Reaction) in rabbiteye blueberry plants from orchards in Louisiana and Mississippi that have experienced plant decline and/or death. X. fastidiosa was cultured from rabbiteye blueberry plants and was detected in one year old blueberry twigs during the winter. Yield data was taken and significant increases in total yield based on average berry weight found between infected and non-infected plants. Progress was made developing disease screening assays using traditional and molecular screening techniques to identify Phytophthora root rot resistant small fruit germplasm and to characterize relevant host/pathogen relationships, the influence of cultural practices, and virulence levels of pathogens. Isolates of the root rot pathogen, P. cinnamomi, have been collected from soil samples near symptomatic blueberry plants in the Gulf South and identified using morphological and molecular techniques. The virulence of these isolates is being determined by growing root rot susceptible blueberry cultivars in soil infested with each isolate. Disease control protocols are being developed based on the cultural practice of removing rosette infected primocanes, which are a source of fungal inoculum, to reduce rosette disease severity in erect blackberry cultivars. Two rosette susceptible blackberry cultivars were planted in replicated plots in Poplarville, MS. The established blackberry planting previously planned for this experiment was abandoned due to a severe infestation of several insect pests including raspberry crown borer and spotted-wing Drosophila fly. In FY 2014 an ornamental plant entomology group collected field survey data at two commercial tree nurseries. The ambrosia beetles had a limited flight range of 25m to 50m beyond the forest's border. Placement of vulnerable tree species beyond those distances, may put the trees out of harm’s way. Kaolin coatings and kaolin with a pyrethroid insecticide were evaluated for the ability to protect trees from ambrosia beetle attack. A leachate recovery system was installed and preliminary studies conducted using a pine bark substrate irrigated at three application rates. The irrigation application rate from drip rings were uniform among the six zones and consistent over time. The irrigation leachate volume can be used to calculate irrigation application rates. A whole pine tree substrate was acquired and will be used this summer in a study to evaluate water and nutrient retention (controlled release fertilizer) in two substrates (pine bark and whole pine tree) under two irrigation application rates. In FY 2014 an ornamental plant pathologist collected spray coverage data at regular distances over 50 foot wide expanses of container-grown azaleas that had been applied from different nozzle size configurations on a commercial airblast sprayer. The association between spray droplet distribution patterns and disease efficacy was compared to determine control levels. The set up of two projects are in progress. A commercial ornamental woody plant nursery has been selected for a multi-year study to determine peak and extended periods of pathogen activity that justify disinfectant treatment of irrigation water needed to prevent or minimize disease damage. Studies are being setup in the greenhouse to evaluate disinfestants, as well as fungicides and cultural controls that can be combined in an integrated disease management program for the purpose of markedly suppressing disease with the least management effort required. In FY 2014 an entomology group has fabricated solitary bee, trap-nesting straws. Some 10,000 straws will be deployed in Texas, Louisiana, Mississippi and Alabama to acquire solitary bees with potential for pollinating southern crops in the spring, summer, and autumn. The three species being targeted are Osmia ribifloris (blueberry pollinator), Osmia chalybea (jujube pollinator), and Megachile scuplturalis (pollinator of edamame and sundry vegetables).

1. Azalea Rhizoctonia web blight controlled in a two step integrated management approach. For decades, control of web blight in commercial nurseries involved spacing container-grown azaleas so air moved around them and applying fungicides sometime during the summer, not always with good results. An Agriculture Research Service scientist with the Thad Cochran Southern Horticultural Laboratory in Poplarville, Mississippi, developed two control strategies, both required learning about the pathogen's behavior. Web blight is complicated because three infective subprocesses are not discreet and may occur simultaneously. Fungicide timing was developed relying on simple decision rules that allow for good control despite yearly differences in disease rates. A newly developed model adds the capability to predict disease outbreaks based on weather in dry, moderate, and wet years. In addition, the ARS scientist discovered the fungus was a hidden stowaway on healthy azalea stems used to propagate next year's shrubs. An environmental friendly hot water treatment eliminates the fungus from stems without harming plant tissue, so pathogen-free plants can be produced. The two step approach builds a core control strategy based on the pathogen's biology at several crop stages of a multi-year production cycle and will serve the ornamental industry for decades.

Review Publications
Yang, X., Copes, W.E., Hong, C. 2014. Two novel species representing a new clade and cluster of Phytophthora. Fungal Biology. 118:72-82.
Hiltpold, I., Adamczyk Jr, J.J., Higdon, M.L., Clark, T.L., Hibbard, B.E. 2014. Carbon isotope ratios document that the elytra of western corn rootworm reflects adult versus larval feeding and later instar larvae prefer Bt corn to alternate hosts. Environmental Entomology. 43(3):840-848.
Armstrong, J.S., Abdel-Mageed, H., Fokar, M., Allen, R., Adamczyk Jr, J.J. 2013. Dietary effects of cotton tissue expressing germin like protein on beet armyworm (Lepidoptera: Noctuidae) growth, survival and pupation. Florida Entomologist. 96(3):693-700.
Thrash, B., Adamczyk Jr, J.J., Lorenz, G., Scott, A.W., Armstrong, J.S., Pfannenstiel, R.S. 2013. Laboratory evaluations of Lepidopteran-active soybean seed treatments on survivorship of fall armyworm (Lepidoptera:Noctuidae) larvae. Florida Entomologist. 96(3)724-728.
Copes, W.E., Barbeau, B., Chastagner, G. 2014. Chapter 21. chlorine dioxide. American Phytopathological Society. p. 251-265.
Copes, W.E., Benson, M.D. 2014. Rhizoctonia web blight. American Phytopathological Society Press. p. 15-19.
Elmer, W.H., Buck, J., Ahonsi, M.0., Copes, W.E. 2014. Chapter 24. emerging technologies for irrigation water treatment. American Phytopathological Society Press. p. 289-301.
Copes, W.E., Benson, M.D. 2014. Rhizoctonia damping-off stem canker and root rot. American Phytopathological Society Press. p. 14-15.