ASHS 2025 Conference

The ornamental crop industry in the United States, is a billion-dollar industry. Weed management in nursery container production is a significant challenge, as weeds compete with ornamentals for essential resources, reducing plant quality, marketability, and overall profitability. Controlling weeds in containers is one of the highest production costs encountered by nursery growers, often exceeding $4,000 per acre. Previous research results have shown that weeds within a restricted area can reduce ornamental growth by 60%. Some of the most problematic weed species identified in the container production includes liverwort, hairy bittercress, oxalis, chick weed, etc. Liverwort is one of the major weed problems in greenhouses and nursery container production. Historically liverwort has been reported as a weed issue in cooler regions of the Northeast and Pacific Northwest regions of the United States. It thrives well in moist, low UV light condition, and in presence of high fertility and a cool temperature. Hence, nurseries and greenhouses are ideal places for their growth. Growers rely mostly on hand weeding to manage these problematic weeds, especially inside the greenhouse production system as there are limitations in applying herbicides within greenhouse conditions. Since hand weeding is very time consuming, laborious, and expensive, there is an immediate need for research to improve chemical weed control practices through alternative pesticides that can be applied to container production and improve growers’ productivity and profitability. New plants are always being added to nursery production so phytotoxicity studies are also required. Some previous research has focused on evaluating synthetic versus organic herbicides for weed control inside greenhouse conditions. However, there is almost no information available on how alternative pesticides such as fungicide or miticides can be used for weed control in container production and whether they will be safe on ornamentals. This significant knowledge gap has led to the development of this master’s research proposal. Hence the objectives of this research proposal are: To evaluate the preemergence efficacies of fungicide and miticide as alternative pesticides on liverwort control; To assess newer herbicide formulations and rates for controlling weeds and phytotoxicity on container-grown woody shrubs; To disseminate the research results to the growers and scientific community. Preliminary results have shown that miticide Tetracurb Max and fungicide Zerotol can provide suppression of liverwort in containers without causing any significant injuries to the woody ornamental shrubs.

The changing climate is impacting weed ecology and growth patterns in agricultural production systems. General understandings of temperature and moisture requirements have been documented for different weed species, however, there is evidence that production practices and environmental factors affect weed species response to temperature and moisture. Laboratory studies were initiated in 2023 at the University of Idaho Research and Extension Center to determine the germination temperature and moisture requirements of Italian ryegrass (Lolium multiflorum) and spring wheat (Triticum aestivum) collected in Idaho and Washington. For the germination temperature requirement experiments, weed populations and wheat cultivars were grown on a thermogradient table with 10 varying temperatures between 4 C and 35 C. In the germination moisture requirement experiments, polyethylene glycol (PEG 8000) obtain 10 different osmotic potentials (0 to -2 MPa) at temperatures >12 C, there were no differences in germination speed and maximum germination between the Italian ryegrass and spring wheat. However, Italian ryegrass had faster germination speed and greater maximum germination at temperatures

Recently, Impatiens necrotic spot virus (INSV), transmitted by the western flower thrips (Frankliniella occidentalis), has emerged as a major limiting-factor in lettuce production, causing up to 100% yield losses in California. Florida, the third-largest lettuce-producing state in the US, following California and Arizona, cultivates approximately 11,000 acres of lettuce annually. While cases of INSV have not been reported in Florida lettuce, F. occidentalis is a common pest in many crops in Florida including lettuce, the virus poses a significant threat to lettuce crops if introduced. Since INSV is exclusively transmitted by thrips, effective thrips management is crucial to mitigate its impact. Currently, management of F. occidentalis mainly relies on pesticides, however, over-reliance on pesticides may lead to insecticide resistance and further raising environmental and health risks. An integrated pest management approach, incorporating thrips-resistant lettuce cultivars as a first line of defense, could provide a sustainable solution to mitigate the possible negative effects of INSV. The aim of this study was to identify lettuce germplasm with resistance to F. occidentalis. In no-choice experiments, 39 lettuce germplasms including commercial cultivars were evaluated for the resistance to F. occidentalis. These germplasms were planted under thrips-free conditions and plants were placed individually to thrips-proof container and infested with 7 female thrips when they developed 5-6 true leaves. The thrips colony was reared on Okeechobee cultivar, a cultivar susceptible to other sap-feeding insects, which was also used as control for the experiments. Fourteen days post-infestation, the number of larvae and adult thrips per plant. Experiments were conducted in an insectary room maintained at 25 ± 1 °C with a photoperiod of 16-hour light and 8-hour dark. Five replicates (plants) were conducted for each lettuce germplasm. Several germplasms, including breeding lines 50100, 70096, and 70882, cultivars such as Bambino, La Brillante, Manatee, Emperor, Hacienda, and Valmaine, as well as plant introductions (PI) 204707 and 251246, exhibited significantly less larvae (Alpha level 0.05) than Okeechobee, suggesting resistance to F. occidentalis. On the other hand, breeding line 60183 and Gator had significantly higher number of larvae thrips than Okeechobee suggesting high susceptibility to F. occidentalis. These findings highlight promising candidates for further identification of genomic regions responsible for resistance against F. occidentalis and to develop resistant lettuce cultivars that could be a first-line of defense against INSV. Since INSV has not been reported in Florida, this underscores the importance of proactive resistance breeding efforts to prevent potential outbreaks.

Air-blast sprayers with intelligent spray technology can apply pesticides more efficiently to tree canopies than conventional sprayers. However, little research has examined their effectiveness for trunk applications to control pests such as flatheaded borer (FHB). FHB larvae chew directly into the trunk upon hatching, necessitating thorough coverage with contact insecticides. Our objective was to explore the potential of using intelligent variable-rate spray technology to achieve thorough coverage on tree trunks. A red maple (Acer rubrum) block was divided into three plot-row-types: single-row (SR), double-row (DR; South and North rows), and triple-row (TR; South, interior, and North rows). Water sensitive paper (WSP) wraps were used to assess spray coverage. Wraps were secured around trunks of ten trees per row at 15 and 40 cm above the ground. Plots were sprayed with water using a Jacto A400/850 air-blast sprayer in constant-rate (CR) and variable-rate (VR) modes using the Smart Apply intelligent spray control system. CR discharged 69% higher spray volume than the VR mode (P < 0.0001). SR had >99% coverage; coverage in SR was not affected by spray mode or wrap height (P ≥ 0.0592). For DR, coverage ranged from 98.4% to 99.9%, and spray mode did not affect coverage on upper wraps (P ≥ 0.0829) within a row, while CR (99.6%) had lower coverage than VR (99.9%; P = 0.0043) for lower wraps in the northern row. However, TR coverage varied with the spray mode and wrap height (P < 0.0001). Upper wraps in the southern and interior rows had higher coverage from CR than VR, 98.6% versus 89.9% (P = 0.0019) and 98.7% versus 78.8% (P = 0.0137), respectively. For lower wraps, both the southern and interior rows had higher coverage from CR than VR, 98.5% versus 93.4% (P = 0.0019) and 99.5% versus 94.0% (P = 0.0137), respectively. Coverage was very high, i.e., ≥98.0% for 18 of 24 treatment combinations and ≥89.9% for 23 of 24 treatment combinations, but did not achieve 100%. There was no advantage to CR for SR or DR. For all plot-row-types and spray modes, the spray rate was higher than desired. CR sprayed 480, 251, and 210 GPA in the SR, DR, and TR plots, respectively, while VR discharged 239, 156, and 140 GPA. Future research should examine the use of adjuvants to increase coverage and determine a coverage range that balances acceptable FHB control, labor costs, and spray volume.

The current study seeks to improve our ability to utilize RNA interference in developing novel tactics for management of arthropod pests related to crop protection and vector mitigation. The use of this technology in the development of novel arthropod control strategies has been substantially limited relative to its potential for implementation, and inherent advantages over traditional means for controlling pests. Past efforts in applying RNA interference as a strategy for management of arthropod pests have been limited by substantial hurdles that this research seeks to address. While the potential for the utility of RNAi in pest management has been recognized in the past several decades, previous research has found that the practicability of the technology in an applied setting is stifled by a number of factors, including the molecular instability of RNA, host susceptibility, evolved resistance, efficacy, and off-target effects. Our interest in exploring the potential for RNAi as a strategy for pest management application comes from recent developments in our investigation into the genomic basis of toxin resistance in insects. This work suggests the vital importance of a family of genes found in all insects that we believe may function as a target for RNAi that would alleviate many of these stated concerns; these genes are directly involved in insect immunity, they are highly conserved throughout insects yet have enough sequence variability to allow for species-specific targeting, and many of these genes cause lethality when silenced using RNA interference. In our analysis, we highlight the potential of this family of genes in being leveraged towards pest management applications across arthropod species; and in our experimental study we target a member of this gene family in 2 species of fruit flies, Drosophila melanogaster and D. sechelia, as well as a target gene that has previously been shown to cause lethality when knocked down in fruit flies. We show that member genes in this family may be an effective target for the development of RNAi based bioinsecticidal approaches, with potential applications in a broad range of arthropod pests.

Viruses are a major biotic threat to cucurbit production in the southeastern United States. Many important cucurbit viruses are transmitted by whiteflies and aphids. Recent cucurbit virus research in Georgia is predominantly focused on whitefly-transmitted viruses (WTVs) and research is lacking on the aphid-transmitted viruses (ATVs) in cucurbit crops of Georgia. This study investigates the occurrence, prevalence, and emergence of ATVs in pumpkin and winter squash crops grown in a vegetable research farm at the University of Georgia-Tifton Campus during the fall season of 2022 and 2023. We screened plants for characteristic virus symptoms such as mosaic, mottling, yellowing, chlorotic spots, vein clearing, shoestring, upward curling, crumpling, blistering, and deformation of leaves. We collected symptomatic leaf samples of pumpkin and winter squash from the field. We processed the leaf samples for small RNA libraries for high-throughput sequencing (HTS) to identify ATVs present in the samples. We amplified viral genes for sanger sequencing and ran quantitative polymerase chain reactions (qPCR) for molecular validation of HTS results. HTS analysis revealed the presence of two ATVs, zucchini yellow mosaic virus (ZYMV) and papaya ringspot virus (PRSV). The qPCR results suggested a significant temporal shift in ATV’s abundance in these two crops. In 2022, PRSV and ZYMV incidence was observed in 56.25% and 31.25% pumpkin leaf samples. In winter squash, PRSV and ZYMV incidence was found in 50% and 32.14% leaf samples. Mixed infection of both viruses was at 28.12% for pumpkin and 25% for winter squash. In 2023, PRSV was not detected in pumpkins, and it was detected at a negligible level (0.62%) in winter squash. ZYMV was predominant in pumpkin (61.25%) and winter squash (42.50%). Phylogenetic analysis of ZYMV-encoded coat protein (CP) and helper component-protease (HC-Pro) suggested a close relationship with the European isolates. However, PRSV-encoded CP and NIa-VPg showed a close relationship with isolates from Australia, Papua New Guinea, Spain, and the United States. To the best of our knowledge, this is the first study to suggest single or mixed infections of ZYMV- and PRSV-infected pumpkin and winter squash in Georgia, USA. The findings of this study will serve as an important foundation for future research to understand the complex interactions between insect-transmitted viruses in cucurbit crops, which is vital for developing resistant cultivars and effective virus management strategies for commercial cucurbit vegetable crop production.

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