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ARS Home » Southeast Area » Poplarville, Mississippi » Southern Horticultural Research Unit » Research » Research Project #438108

Research Project: Management of Diseases, Pests, and Pollinators of Horticultural Crops

Location: Southern Horticultural Research Unit

2022 Annual Report

1. Develop environmentally friendly strategies for the control of small fruit diseases based on chemical, biological, and/or cultural control by conducting basic and applied research on the epidemiology, pathogenesis, and genetics of small fruit pathogens and their hosts. 1.1. Assess the effect of supplemental lights (LED, UV-B) on anthracnose pathogen growth in culture and on infection of greenhouse grown strawberries. 1.2. Assess the use of cover crops to reduce root rot pathogen populations in blueberry fields. 1.3. Develop a protocol to identify anthracnose resistant strawberry seedlings using non-viable culture filtrates of the anthracnose fungi. 2. Expand the scope and efficacy of plant pathogen sanitation technologies at multiple disease management scales involving propagation, general sanitation, and seasonal irrigation water treatment for ornamental production systems. 2.1. Evaluate spatial distribution of bacteria causing bacterial gall of Loropetalum in commercial nurseries and its association with stem cuttings used for propagation. 2.2. Determine rate activity responses for major commercial disinfestants against bacterial, fungal and viral plant pathogens. 2.3. Develop integrated preventive and reactive disease management strategies to control Pseudomonas, Colletotrichum, and Phytophthora in propagation facilities. 2.4. Develop concentration-time (CT) rates with water quality and temperature as covariates for treatment of Phytophthora nicotianae in irrigation water. 2.5. Model the relationship of seasonal dispersal of Phytophthora zoospores in recycled irrigation water with plant disease symptom development and weather conditions. 3. Discover, test, and develop new conventional and organic controls for the Spotted Wing Drosophila (SWD) and develop improved bee-safe practices for their application. 3.1. Discover and test erythritol, its derivates, essential oils, and insect growth regulators (IGRs) for control against SWD and other serious horticultural insect pests. 3.2. Test for additive or synergistic activity from combinations of select compounds from sub-objective 3.1 with biopesticides. 3.3. Test health safety of compounds from sub-objectives 3.1 and 3.2 to honey bees and important native bee crop pollinators. 4. Develop new management and conservation techniques for honey bees and important wild native bee pollinators for small fruit, vegetable and ornamental crop production. 4.1. Collect cocoons from trap-nests for managing orchard bees and chimney bees as fruit pollinators. 4.2. Develop and implement a pollinator release program. 4.3. Assess effects of common and new insecticides on these and other native bee pollinators of horticultural food crops. 4.4. Assess the use of soybean cultivars as bee forage for native and honey bees during the summer dearth along the Gulf Coast.

Evaluate influence of multiple light spectra, including UV-B light, on strawberry plant growth and as a way to inhibit germination and growth of anthracnose pathogens, thereby reducing disease. Assess effect of rotational cover crops (legume, brassica and grass), fallow and chemical treatments on Phytophthora populations in the soil and on severity of root disease on blueberry in replanted fields. Develop plant screening protocols using non-viable filtrates with presumed toxins of anthracnose pathogens to identify anthracnose resistance in strawberry seedlings. Sample for and analysis for distribution patterns of the bacterial knot pathogen on Loropetalum nursery stock to develop strategies for propagating pathogen-free plants. Identify differences in pathogen sensitivities, substrate demand loads and environmental factors that favor and interfere with disinfestant activity for several disinfestant chemical classes. Evaluate what combination of disease control practices allow for minimum levels of integrated management needed to control several major pathogens in woody plant propagation. Identify water quality and environmental factors that require adjustment in disinfestant concentration exposure to maintain control of Phytophthora in irrigation water. Monitor Phytophthora levels in pond water, the resulting disease progress on woody plants irrigated with the pond water and correlate these with favorable environmental conditions. Investigate how chemical formulation affects the activity of sugar alcohol pesticides, essential oils, and insect growth regulators applied to different stages of the spotted-wing Drosophila (SWD) fly. Identify what combination of chemicals previously tested by this research unit provide maximum mortality of SWD. Evaluate health effects on honey bees, orchard bees, chimney bees, and southeastern blueberry bees exposed to the chemicals evaluated by this research unit for SWD control. Collect orchard bees and chimney bees from across the southern U.S., establish them by commercial blueberry fields in Mississippi, determine their suitability as a pollinator and develop colony rearing practices. Establish orchard bee and chimney bee colonies near cooperating blueberry fields and monitor seasonal dispersal behaviors. Evaluate health effects on bee pollinators exposed to various insecticides, then assay for gene activity, enzyme activity and protein profiles. Evaluate the bloom period of soybean cultivars planted at several dates and monitor the feeding activity and health of native and honey bees.

Progress Report
An ARS plant pathologist and a plant geneticist at Poplarville, Mississippi in collaboration with university researchers at Poplarville, Mississippi and Fort Pierce, Florida evaluated the effect of ambient light and supplemental light emitting diodes (LEDs), wide spectrum fluorescent, and ultraviolet B (UV-B) light treatments on plant growth and anthracnose disease response of strawberries grown in a greenhouse. A significant difference was found due to light treatment and the relative chlorophyll content and plant growth parameters of cultivars. The study showed an effect of supplemental light on several strawberry plant growth parameters, including a harmful effect from high intensity red LED irradiation. The Southern Horticultural Research unit in collaboration with university researchers at Mississippi State University, Starkville, Mississippi collected Loropetalum plants exhibiting symptoms of bacterial knot from commercial nurseries in Alabama, Louisiana and Mississippi. The whole genome of Pseudomonas amygdali pv. loropetali was sequenced, genes identified and annotated. The development of primers is in progress and will be used for identification of the pathogen in a field spatial analysis study. We performed systematic reviews and meta-analyses in collaboration with a university researcher at North Carolina State University, Raleigh, North Carolina to summarize existing knowledge on the efficacy of peroxy disinfestant compounds for controlling fungal plant pathogens in agricultural and horticultural crop production systems. Results showed the current recommended rates and contact times of commercial products are generally effective disinfestants, but efficacy can be influenced by the sensitivity of fungal genera, the target material being treated, and by what peroxy product is applied. A pathologist characterized evaporative rates of commercial disinfestants applied to multiple production materials under a range of environmental conditions. Further research will test how evaporative rates affect contact time and efficacy of the disinfestant products against Colletotrichum camelliae. An ARS entomologist in Poplarville, Mississippi, in cooperation with scientists at the University of Hawaii, tested two natural compounds from pennyroyal and basil plants. When formulated into a soapy emulsion, these monoterpene compounds killed 65% of spotted-wing drosophila flies in the field and 100% under laboratory conditions. In field trials, these two compounds were as effective as the commercial biopesticides Grandevo, Entrust, and Pyganic. However, mixtures of these compounds with erythritol are not recommended due to an observed 30% increase in foliar injury to blueberry bushes. Further research is directed at improving the formulation for greater rain-resistance during the wetter months of May and June during southern blueberry harvest. The current formulation of these two compounds posed no danger to native bee pollinators of blueberry; bees foraged normally and green fruit sets from 60-70% were achieved. The entomologist, by following the path of hurricane Ida (2021), identified 5 active aggregations of wild chimney bees nesting in the clay root plates of fallen hardwood trees in the Mandeville, Louisiana area in 2022. Females were active from March to June, and thus, will be collected in the fall, incubated, and released on flowering blueberries in 2023. Screenhouse repairs, including a new Lumite cover, are underway to house chimney bees for their evaluation as manageable fruit pollinators. An ARS entomologist conducted field surveys for chimney bee nests and discovered that the bee is considerably more abundant in marshland and other coastal habitats. Thus, bee cocoons would require transport to more inland fruit fields that are supplied with sun-dried clay nesting domiciles. Plywood molds for pouring in mud have been fabricated so that clay domiciles can be fashioned during the winter of 2022. Harvesting cocooned bees will commence in the fall of 2022. Southern Horticultural Research Unit working with professors from Mississippi State University and the University of Southern Mississippi developed laboratory bioassays for measuring the sensitivities of native bees to sublethal doses of a persistent neonic insecticide. During our testing, we measured the adult longevities and duration of paralysis for honey bees and 11 species of wild bees feeding on sublethal concentrations of imidacloprid. Chosen bee species for the assays were important horticultural crop pollinators such as honey bees, bumble bees, southeastern blueberry bees, squash and pumpkin bees, sunflower bees, okra bees and 7 other species. Bioassay units were made from plastic cups and jars, where bees were fed from dental wicks saturated with water containing four sublethal doses of the neonic, imidacloprid. An ARS research entomologist at Poplarville, Mississippi in collaboration with university researchers at the University of Saint Thomas, Minnesota have demonstrated the effects of fungicides commonly applied to bee pollinated crops on honey bee cell health using an in vitro model. We have documented the effects of commercial pesticide formulations commonly found in landscapes on honey bee cell health using a cell culture system established from honey bee tissues. An ARS research entomologist at Poplarville, Mississippi assisted university researchers at the University of Belgrade, Serbia on how to culture honey bee cells for toxicological studies. An ARS research entomologist at Poplaville, Mississippi has established a Cooperative Research and Development Agreement to develop remote monitoring of honey bee flight paths and mapping of visitation in blueberry.

1. Chlorine disinfestants often work well but not always, why is that. Meta-analyses were done to find out how consistently chlorine products kill plant pathogens on agricultural and horticultural production surfaces, since we expect the products to be reliable. ARS researchers in Poplarville, Mississippi, compiled data from a broad research base and analytical comparisons made between fungal, oomycetial, bacterial and viral plant pathogens present on various types of production surfaces. The magnitudes of control efficacy varied from high, moderate to poor levels, thus were not as reliable as expected. Control varied between pathogen genera for all pathogen types, indicating organisms possibly vary in sensitivity to chlorine. Chlorine disinfestants provided the most consistent control of fungi in solution, good control on most materials and the least consistent control on wood surfaces, while only minor differences in control occurred with bacteria, oomycetes and viruses present on the same materials. Results demonstrated that while chorine products can be effective disinfestants additional research is needed to better understand the factors influencing efficacy, so growers can more reliably obtain the level of disease control needed to produce quality plant products.

2. Two natural substances from wild herbs are excellent insecticides against an invasive berry pest, the spotted-wing Drosophila (SWD). SWD is an intractable fruit pest of small fruit crops. In conventional agriculture, this fly is effectively controlled by powerful, synthetic insecticides. In contrast, organic berry producers have only two control options, but the effectiveness of these products varies considerably. New products are urgently needed to protect organic berry operations. ARS researchers in Poplarville, Mississippi, and Miami, Florida, along with cooperators at the University of Hawaii have identified two compounds from pennyroyal and basil plants that were neurotoxic to SWD and killed >60% of eggs and adult flies in blueberry fields. Laboratory tests revealed that these compounds eliminated SWD reproduction at concentrations =0.5%. These monoterpene substances are readily available and are being formulated as a new organically certified biopesticide targeting small-bodied crop pest.

3. Certain bee species are not equally susceptible to the harmful effects of long-lasting neonic insecticides. Persistent insecticides such as neonicotinoids have been implicated in global pollinator losses. However, current studies have only focused on manageable crop pollinators such as honey bees and bumble bees. ARS researchers in Poplarville, Mississippi, examined the sublethal effects of residual pesticides on a whole 03 community of crop pollinators, both managed and wild. Bee species displayed no visible tremors, except for a small sweat bee, which exhibited brief convulsions at the highest dose. The insecticide when ingested did shorten the lifespans of all tested solitary bees. Sweat bees, honey bees, and okra/rose mallow bees lived the longest, approximately 10 to 12 days. Although susceptibility to imidacloprid-induced paralysis was greatest in bumble bees, social bees generally tolerated this insecticide better than did solitary species. These data confirm that any reduction in the lifespan of bees would profoundly reduce brood production, which could eventually lead to local extinctions of some of the more susceptible pollinator species.

Review Publications
Kumar, D., Alburaki, M., Tahir, F., Goblirsch, M.J., Adamczyk Jr, J.J., Karim, S. 2022. An insight into the microRNA profiles of an ectoparasite mite Varroa destructor (Acari: Varroidae), the primary vector of Deformed Wing Virus (DWV) of the honey bee Apis mellifera L. Frontiers in Cellular and Infection Microbiology.
Meikle, W.G., Colin, T., Adamczyk Jr., J.J., Weiss, M., Barron, A. 2022. Traces of a neonicotinoid pesticide stimulate different honey bee colony activities, but do not increase colony size or longevity. Ecotoxicology and Environmental Safety. 231. Article 113202.
Hamm, T., Boggess, S., Sthapit Kandel, J., Staton, M., Huff, M., Hadziabdic, D., Shoemaker, D., Adamczyk Jr, J.J., Nowicki, M., Trigiano, R. 2022. Development and characterization of 20 genomic SSR markers for ornamental cultivars of weigela. Plants. 11(11):1444.
Smith, B.J., Rezazadeh, A., Stafne, E., Sakhanokho, H.F. 2022. Effect of LED, UV-B, and fluorescent supplemental greenhouse lights on strawberry plant growth and response to infection by the anthracnose pathogen, Colletotrichum gloeosporioides. HortScience. 57(8):856–863.
Sakhanokho, H.F., Islam-Faridi, N., Smith, B.J. 2022. Determination of genome size and chromosome number of a Ziziphus species (Z. mauritiana Lam.) from eastern Senegal. HortScience. 57(3):349-352.
Sakhanokho, H.F., Nurual, I., Smith, B.J. 2022. Nuclear DNA content and chromosome number determination in a Sahel medicinal plant, Combretum micranthum G. Don. Journal of Crop Improvement.
Copes, W.E., Ojiambo, P.S. 2021. Efficacy of hypochlorite as a disinfestant against fungal pathogens in agricultural and horticultural plant production: a systematic review and meta-analysis. Phytopathology. 111:1369-1379.