Location: Southern Horticultural Research Unit
2020 Annual Report
Objectives
Objective 1. Develop integrated strategies to control invasive diseases and pests
within the context of small fruit production systems of the Gulf Coast.
Sub-objective 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.
Sub-objective 1.2. Develop and evaluate Integrated Pest Management (IPM) strategies involving selective chemical application.
Sub-objective 1.3. Determine pathogen lifecycle events and spread patterns of bacterial leaf scorch, a new and emerging disease of blueberries in the Gulf South.
Sub-objective 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.
Sub-objective 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-objective 2.1. Develop a three-step ‘push-pull’ management strategy for protecting vulnerable nursery tree stock from ambrosia beetles.
Sub-objective 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.
Sub-objective 2.3. Determine optimal timing of disinfestant to restrict pathogen dispersal through irrigation water and limit plant disease.
Sub-objective 2.4. Develop a comprehensive preventive and reactive disease management strategy to control Pseudomonas, Colletotrichum, and Rhizoctonia in plant propagation facilities.
Sub-objective 2.5. Develop an integrated disease management strategy to control Leyland cypress blight in ornamental plant nursery production.
Sub-objective 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.
Approach
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
This is the final report for this project which has been replaced by new project #6062-21420-004-00D, "Management of Diseases, Pests, and Pollinators of Horticultural Crops."
ARS researchers in Poplarville, Mississippi, and Corvallis, Oregon, discovered that some wild and cultivated blueberry host fruits, especially fruit species found within the pest’s native range, showed resistance to egg-laying by spotted-wing Drosophila (SWD) flies. However, SWD flies were able to reproduce in both optimal and sub-optimal habitats. Potentially, new varieties of blueberry can be developed and released with some resistance to SWD attack. ARS researchers in Poplarville, Mississippi, and New Orleans, Louisiana, discovered two common and affordable sugar alcohols can be effective and environmental-friendly insecticides, possibly marketable as an organic product, that target SWD flies. The two compounds have synergistic properties, which captured the attention of international and national interests with non-disclosure agreements being signed with Biologic Insecticide LLC (Canada/U.S.) and Marrone Bio Innovations, Inc. (U.S.). Continued research in 2020 substantiated that erythritol is synergistic with a commercial microbial-based biopesticide (Grandevo®) by doubling the effectiveness in laboratory and field research. ARS researchers in Poplarville, Mississippi, Miami, Florida, and Oxford, Mississippi, have completed essential oil screening and found that extracts from two species of abundant New World Jatropha, also called belly plants, and most cultivars of rose geranium displayed better control of ornamental insect pests than commercially available neem oil or malathion. These results suggest these two plants may be potential sources of new biopesticides.
An ARS researcher in Poplarville, Mississippi, in collaboration with researchers at Louisiana State University, Baton Rouge, Louisiana, reported that seven rabbiteye blueberry cultivars and one southern highbush blueberry cultivar inoculated with a X. fastidiosa isolate from rabbiteye blueberry did not exhibit any symptoms of bacterial leaf scorch disease within 9 months. They described a new strain of the bacterial pathogen recovered from rabbiteye blueberry plants growing in commercial fields that is pathogenic to southern highbush blueberry and recommended that blueberry growers should plant bacteria-free rabbiteye blueberry plants into fields that contains susceptible southern highbush blueberry cultivars. An ARS researcher in Poplarville, Mississippi, and Mississippi State University researchers in Poplarville, Mississippi, developed an effective detached-leaf assay to rapidly screen strawberry germplasm for resistance to anthracnose crown rot. They determined this assay was a useful tool for mapping germplasm for resistance genes and evaluating pesticide efficacy. The same research team evaluated protocols to control blackberry rosette disease that involved removal of rosette infected primocanes, which are the initial source of fungal inoculum, from two rosette susceptible erect blackberry cultivars, but found no significant differences between treatments. They also reported that a thornless trailing blackberry cultivar exhibited greater incidences of white drupelet disorder than two erect, thorny cultivars growing in their research plots.
ARS researchers in Poplarville, Mississippi, and Wooster, Ohio, as well as researchers from Virginia Polytechnic Institute, Virginia Beach, Virginia and Tennessee State University, McMinnville, Tennessee, developed a mass-trapping control strategy as part of a push-pull strategy using slow release ethanol, kaolin clay, and pyrethroid sprays to intercept and kill 80- 95% of female ambrosia beetles before the insects have an opportunity to attack and infect host trees with a deadly symbiotic fungus.
An ARS researcher in Poplarville, Mississippi, in collaboration with researchers at Virginia Polytechnic Institute, Virginia Beach, Virginia documented that the predominate Phytophthora species recovered in recycling irrigation reservoirs in an Alabama and Mississippi nursery were of low risk for causing plant disease, thus current pathogen testing assays that identify Phytophthora only to genus are not specific enough to confirm a need to treat irrigation water. An ARS researcher in Poplarville, Mississippi, in collaboration with researchers at Virginia Polytechnic Institute and University of Maryland documented that water quality varied substantially between containment reservoirs at ornamental plant nurseries but all water sources were suitable for irrigating plants. Suitability of water was also compared to Environmental Protection Agency ecological water quality standards in the U.S. This information expands our general knowledge on water quality used for irrigation and provides criteria for evaluating the impact of water quality on efficacy of disinfestant water treatments. An ARS researcher in Poplarville, Mississippi, a Mississippi State University researcher in Poplarville, Mississippi, and a researcher at the University of Southern Mississippi, Hattiesburg, Mississippi, demonstrated disinfestant classes differed in their ability to eliminate the bacteria, Pseudomonas amygdali, that causes Loropetalum bacterial gall from different types of production surfaces. This information is a major component towards the goal of propagating pathogen-free Loropetalum plant stock. An ARS researcher in Poplarville, Mississippi, in collaboration with an extension specialist at the University of Georgia modeled spore dispersal patterns of Passalora sequoiae, the cause of Leyland Cypress blight. The model showed that the seasonal shift in cooler temperatures, lower vapor pressure deficits and a lower solar radiation in the fall favored higher production and dispersal of P. sequoiae conidia than during summer weather conditions. ARS researchers in Poplarville, Mississippi, and Dawson, Georgia, and researchers at Colorado State University, Fort Collins, Colorado, generated the first draft assembly of the whole genome sequence of P. sequoiae as a resource for primer development and to investigate genotype diversity.
ARS researchers in Poplarville, Mississippi, and a researcher at Mississippi State University, Mississippi State, Mississippi assessed the sublethal and lethal effects of neonicotinoid insecticides on horticulturally important native bee species. The same team, in cooperation with researchers at Auburn University, Auburn, Alabama; University of Florida, Gainesville, Florida and University of Bern, Switzerland, assessed the sensitivity of the endemic digger bees, Anthophora abrupta, to imidacloprid insecticides. The endemic digger bee is being investigated as a new manageable pollinator of southern blueberries. Results indicate that certain native bee species have different responses to low amounts of neonictinoid insecticides compared to honey bees. Furthermore, these data will be useful to regulatory agencies in determining acceptable risk levels to the health of less common, but ecologically important native bees. ARS researchers in Poplarville, Mississippi, and Mississippi State University researchers evaluated the comparative effects of a sugar-rich substitute patty, a pollen substitute, and bee bread on worker longevity within bioassays. Adult honey bees under captive conditions survived better when sugar, preferably sucrose, was used as the sole food source, while pollen-rich diets proved harmful. This information will assist scientists in developing artificial food sources for maintaining bees outside of the hive by alleviating stress and maximizing survival of experimental honey bee subjects used in bioassays. In addition, this information will assist beekeepers in selecting the best ingredients when providing supplemental artificial food sources to hives.
Accomplishments
1. Genotyping Xylella fastidiosa recovered from rabbiteye blueberry in Louisiana. Bacterial leaf scorch, caused by the bacterium Xylella fastidiosa, is an important emerging disease of southern highbush blueberry that has been reported in rabbiteye blueberry, the primary blueberry species grown commercially in Louisiana. Reports of Xylella fastidiosa infection in rabbiteye blueberry present a potential problem if it reduces yield in rabbiteye or has possibility of spreading from rabbiteye to the more susceptible southern highbush blueberry cultivars. An ARS researcher in Poplarville, Mississippi, in collaboration with researchers in Baton Rouge, Louisiana, sampled commercial rabbiteye blueberry plants in Louisiana for the prevalence of X. fastidiosa infections. Three genotypes of X. fastidiosa were identified from rabbiteye blueberry in Louisiana. Two new genotypes were identified and their risk of spread to other plants needs further study. One genotype was identical to those reported in southern highbush blueberry in Georgia and in native blueberry species in Texas, thus this genotype poses a high risk for being spread to the more susceptible southern highbush blueberry cultivars. The threat is further challenging, since rabbiteye plants do not always show distinctive symptoms of bacterial leaf scorch. This critical information will be beneficial to growers, crops advisors and plant pathologists to increase awareness of this disease. Spread of the disease can be reduced by planting leaf scorch free stock when introducing rabbiteye plants into fields that contain or adjacent to healthy southern highbush cultivars.
2. Bee colonies foraging in agricultural landscapes are potentially exposed to numerous pesticide applications. Honey bees forage across a large area, continually scouting the local landscape for ephemeral food resources. Beekeepers often rely on flowering plants in and around irrigated farmland to maintain their colonies during dry seasons, despite the potential risk of pesticide exposure. Recent declines in pollinator abundance and diversity have focused attention on the role of pesticides and their effects on honey bee health. ARS researchers in Poplarville, Mississippi, and researchers at the University of Arkansas, Mississippi State University and University of Tennessee examined two types of landscapes, an intensive agricultural setting and a rural setting without intensive agriculture, existing within a two-mile (3.2 km) radius of honey bee colonies. More than 10,000 acres of agricultural land were surveyed to quantify the area of cultivated crops and the area treated with pesticides. Samples of honey, bee bread (stored pollen), beeswax, and adult bees were collected from hives foraging in each landscape type and screened for pesticide residues to determine if foraging bees were transporting pesticides to hives. Some samples of bee bread and honey did contain pesticide residues, but these were below known lethal dose levels for honey bees. Beeswax samples contained the highest levels of contamination, but most were still relatively low. Samples were screened for 174 common agricultural pesticides and metabolites, but only 26 compounds were detected during the two-year study. While the residues detected in this study did not pose an acute lethal risk to adult honey bees, this study did not measure sublethal effects on bee colony health or performance, which merit further investigation.
3. Producing Loropetalum shrubs free of the Loropetalum bacterial knot disease. Stem galls were first observed on Loropetalum shrubs in the U.S. in 2012 and a bacterium, now named Pseudomonas amygdali pv. loropetali, was identified as the causative organism in 2013. The disease quickly became a dominating problem in Loropetalum propagation in commercial plant nurseries in the southeastern U.S., and no proven control treatments are available. Disinfestants that are commercially labeled for use in ornamental plant production systems were evaluated for their ability to kill the bacterium. An ARS researcher in Poplarville, Mississippi, in collaboration with researchers at the University of Southern Mississippi and Mississippi State University found the choice of disinfestant depended on what surface was being treated. Clorox, Green-Shield II, KleenGrow, and Virkon S eliminated the bacterium from metal surfaces, while only Clorox and Virkon S provided comparably control on pressure-treated wood surfaces and only Chlorox eliminated the bacterium from the bark of Loropetalum stems used for propagation. Other products tested were ineffective. This information will be useful to commercial plant producers and crop advisors. Based on these results, Loropetalum stem cuttings potentially infested with P. amygdali pv. loropetali could be treated for 6 minutes in 10% bleach, while collection containers and table tops should be disinfested between each batch with appropriate disinfestants.
4. Image analysis and visual ratings of diseased strawberry leaves provide comparable measures of anthracnose resistance. Disease resistant cultivars are the most desirable method to control diseases such as anthracnose crown rot of strawberry; however, their development requires the time-consuming evaluation of the disease response on thousands of seedlings. Visual rating scales and image analysis of diseased tissue are two methods available to assess the disease response on inoculated seedlings. ARS researchers in Poplarville, Mississippi, compared these two methods by inoculating detached leaves of anthracnose susceptible and resistant strawberry clones with an isolate of the fungal pathogen. Detached leaf inoculations provided a simpler and faster screening method than using whole plants. Anthracnose disease symptoms were assessed quantitatively via computer-based image analysis to determine percentage lesion area and qualitatively by using a visual disease severity rating scale. Each method provided different advantages. The visual ratings allow a rapid initial screening of large numbers of strawberry seedlings. The electronic imaging takes longer but provides a more critical assessment that can be used selectively to compare key anthracnose resistance or susceptibility selections for the developmental selection of potential new cultivars. These methods will be beneficial to plant breeders, plant pathologists, and horticulturists developing new disease-resistant strawberry cultivars, mapping germplasm for resistance genes, and testing pesticides.
Review Publications
Copes, W.E., Mavrodi, O.V., Mavrodi, D.V. 2020. Control of Pseudomonas amygdali pv. loropetali on metal, wood, and Loropetalum chinense stem surfaces. Plant Health Progress. 20(4):270-277. https://doi.org/10.1094/PHP-09-19-0068-RS.
Zawislak, J., Adamczyk Jr, J.J., Johnson, D.R., Lorenz, G., Black, J., Hornsby, Q., Stewart, S.D., Joshi, N. 2019. Comprehensive survey of area-wide agricultural pesticide use in southern United States row crops and potential impact on honey bee colonies. Insects. 10(9):280. https://doi.org/10.3390/insects10090280.
Alburaki, M., Karim, S., Lamour, K., Adamczyk Jr, J.J., Steward, S. 2019. RNA-seq reveals disruption in honey bee gene regulation when caged and deprived of hive conditions. Journal of Experimental Biology. https://doi.org/10.1242/jeb.207761.
Miller-Butler, M.A., Curry, K.J., Blythe, E.K., Smith, B.J. 2019. Evaluation of detached strawberry leaves for anthracnose disease severity using image analysis and visual ratings. HortScience. 54(12):2111-2117. https://doi.org/10.21273/HORTSCI14321-19.
Stephenson, R.C., Coker, C.E., Bachman, G.R., Posadas, B.C., Harkess, R.L., Adamczyk Jr, J.J., Knight, P.R. 2019. Economic effect of insect pest management strategies on small-scale tomato production in Mississippi. HortTechnology. 30(1):64-75. https://doi.org/10.21273/HORTTECH04435-19.
Ferguson, M., Clark, C.A., Smith, B.J. 2020. Genotyping Xylella fastidiosa in rabbiteye blueberry in Louisiana, USA. European Journal of Plant Pathology. 157:679-683. https://doi.org/10.1007/s10658-020-02017-6.
