ASHS 2024 Conference

A Water Soluble β-triketone Enriched Extract of Manuka Oil has Increased Efficacy Compared to Vinegar and D-Limonene in a Field and Greenhouse Evaluation - Casey Barickman
Weed Control in Bell Pepper after Herbicide Application in a Reduced Sunnhemp Cover Crop Population. - Peter Dittmar
Assessing the Effects of Container Sizes and Weed Densities on Weed-ornament Competition in Nursery Container Production - Debalina Saha
Herbicide-Resistant Italian Ryegrass in Oregon Hazelnut Orchards: Evaluating Nonchemical and Chemical Methods - Marcelo Moretti
Limiting Liverwort Growth by Allelopathic Effects of Organic Mulches in Ornamental Production - Manjot Sidhu
Effect of Application History on Preemergence Herbicide Persistence - Travis Gannon

Weed management strategies for specialty and organic crop production are challenging due to limited chemical weed control products with good efficacy that are cost effective. The need for new bioherbicide modes of action has become increasingly urgent in modern agriculture as most bioherbicides have nonspecific modes of action with no systemic activity. Introducing new modes of action is essential to diversify weed control strategies, minimize the risk of resistance development, and ensure sustainable weed management practices. By fostering innovation in bioherbicide development and promoting the use of novel modes of action, we can safeguard our agricultural systems, reduce the environmental impact of weed management, and maintain the ability to feed a growing global population while preserving the long-term health of our ecosystems. Manuka oil is derived from the leaves and branches of the Manuka tree (Leptospermum scoparium) and contains β-triketones. The β-triketone rich fraction contains leptospermone and inhibits a key enzyme, p-hydroxyphenylpyruvate dioxygenase (HPPD). This process directly inhibits carotenoid biosynthesis, upstream in the biochemical pathway, which causes damage to the photosynthetic apparatus and leads to bleaching of the leaf tissue which eventually kills the plant. The β-triketone extract at 2% and 4% had up to 97% control against different weed species in field and greenhouse evaluations. The β-triketone extract was significantly more efficacious verse other bioherbicides such as the 20% vinegar and 12.5% D-limonene. Additionally, the β-triketone extract was just as effective as the 2% glyphosate treatment in the greenhouse evaluation against Amaranthus palmeri and Digitaria sanguinalis. The β-triketone extract also reduced Cyperus esculentus growth by 70% at 9 days after treatment. Thus, there is significant evidence that commercializing a water soluble β-triketones enriched extract of Manuka oil can be an effective weed control strategy in crop production systems, especially in specialty and organic cropping systems where the need of bioherbicides is critically imperative.

Sunnhemp cover crop seed germination can be lowered due to poor seed quality, incorrect planting depth, or adverse weather effects. The objective of this research is to evaluate weed control by herbicides in a reduced sunnhemp population. Research trials were conducted at the Plant Science Research and Education Unit, Citra, Florida, and the Syngenta Vero Beach Research Center, Vero Beach, FL. The treatments were sunnhemp at 44.83 kg/ha, sunnhemp at 22.4 kg/ha ( no herbicide, bentazon at 1.12 kg/ha, sulfentrazone at 0.14 kg/ha, halosulfuron at 0.04 kg/ha, glyphosate at 5.5 kg/ha followed by glyphosate at 5.5 kg/ha, and oxyfluorfen at 0.56 kg/ha), and a nontreated weed fallow. Sunnhemp was planted in Citra on July 18, 2023 and in Vero Beach on July 27, 2023; herbicides were applied 2 weeks after planting when the sunnhemp were 15 to 25 cm tall. After 8 weeks of growth, the sunnhemp was mowed and the field was prepared for laying plastic and planting bell pepper. The oxyfluorfen caused significant injury to the sunnhemp; this treatment had similar broadleaf, grass, and nutsedge populations to the weed fallow. In Citra at 14 and 28 days after application, bentazon, sulfentrazone, or halosuluron had lower populations than sunnhemp at 22.4 kg/ha alone, but at cover crop termination all the cover crop treatments had similar nutsedge control. All cover crop alone and cover crop herbicide treatments had similar grass and broadleaf control at crop termination. In the bell pepper crop at Vero Beach, oxyfluorfen had greater nutsedge populations than all the other treatments. Crop yields were similar among the cover crop alone or with a herbicide. The application of a herbicide in a reduced cover crop population is not necessary for increased weed control in a fall cash crop. However, the reduced cover crop population in this study was artificially created so the sunnhemp population was equal spaced through the entire plot. If the sunnhemp is significantly impacted like the oxyfluorfen treatment, then more intense recovery action may be necessary.

Effective weed management strategies are essential for producing high-quality and successful ornamentals in nurseries and greenhouses. Weeds can affect both the productivity and quality of ornamentals, especially in containers where nutrient and moisture availability are limited, due to restricted space. The objective of this study was to determine how different types of weed species at various densities and in different container sizes affect the growth of ornamental plants. Two rounds of greenhouse experiments were conducted at the Horticulture Teaching and Research Center, Michigan State University, in summer and fall 2023. Seeds of large crabgrass {Digitaria sanguinalis (L.) Scop} and smooth pigweed (Amaranthus hybridus L.) were grown separately until they attained the 4-6 leaf stage. Liners of hydrangea {Hydrangea macrophylla (Thunb.) Ser.} and syringa (Syringa vulgaris L.) were planted in containers of three different sizes 0.67 gallons (2.54 liters), 1.5 gallons (5.67 liters), and 3 gallons (11.35 liters) containing standard bark-based substrate amended with controlled-release fertilizer. All plants received 0.5 inches (1.3 cm) of water thrice daily and were allowed to grow till they were well established. Then the weed seedlings of large crabgrass and smooth pigweed were carefully transplanted to each container-grown ornamental plant at different densities of 0,1,3,6 per pot, with the density of 0 being the control set. After weed transplantation, all pots were maintained inside the greenhouse for 8 weeks. The experimental design utilized a randomized complete block design with six replications per treatment. Initial and final growth indices of ornamentals were recorded. At 8 Weeks After Potting (WAP) fresh weights of both the weed species and the ornamentals were recorded separately. All data were analyzed in SAS by ANOVA and the Tukey’s HSD test were performed to separate out the means. Results showed that final growth indices of hydrangea were significantly higher than syringa and maximum in 3-gallon containers. Overall, large crabgrass at density of 6 was more competitive than smooth pigweed and hydrangea performed better than syringa in 3-gallon container size in competing the weed species.

Herbicide-resistant Italian ryegrass (Lolium multiflorum Lam.) presents a significant challenge in hazelnut orchards across Oregon, with confirmed resistance to multiple herbicide modes of action groups (1, 2, 9, 10, 15, and 22). Four field studies were conducted in 2023 to evaluate nonchemical and chemical methods for controlling Italian ryegrass during spring. Tested treatments included mowing at 2 km h-1, electric weeding control (EWC) at 15 MJ ha-1 (2 km h-1), and glufosinate application at 1.68 kg ai ha-1, administered once or twice. Furthermore, combinations of EWC with mowing or glufosinate were examined, resulting in eleven treatments. EWC was performed using alternating current and 30 kW (EH-30 Thor, ZassoTM), treating swaths 1.2 m wide. Assessments conducted 56 days after initial treatment (DAIT) revealed that single mowing showed no significant difference compared to untreated plots. However, when mowing was performed twice, it led to a 30% reduction in inflorescence density and an 84% reduction in weight. EWC, applied once or twice, resulted in significant decreases in Italian ryegrass inflorescence density (51-58%), weight (55-73%), and shoot weight (45-75%) compared to untreated plots, with no significant differences observed between single or double applications. Similarly, glufosinate applied once or twice substantially reduced Italian ryegrass inflorescence density (68 to 86%) and weight (73 to 93%). Combinations of EWC with mowing or glufosinate demonstrated high efficacy, achieving control rates of 89 to 96% and exhibiting comparable efficacy to two applications of glufosinate (96%). These findings suggest that EWC, when applied during the spring period, can effectively control Italian ryegrass, offering comparable efficacy to glufosinate and superior efficacy to mowing.

Liverwort (Marchantia polymorpha) is one of the problematic weeds in ornamental crop production that deteriorates the quality and aesthetic value of ornamentals. To study the effectiveness of allelopathic properties of organic mulch extracts, six different organic mulch materials including rice hull (RH), cocoa hull (CH), pine bark (PB), maple leaf (ML), shredded cypress (SC) and red hardwood (HW) were used for obtaining mulch extracts. The extracts were prepared by following the modified EPA 1312 synthetic precipitation procedure. In the lab experiment, the mulch extracts obtained were used to impregnate agar media at an increasing dose at either 1x (2ml), 2x (4ml), 3x (6ml), and 4x (8ml) rates. Ten gemmae were transferred to the culture medium in each petri dish and all petri dishes containing gemmae were maintained inside the growth chamber. Data was recorded for number of gemmae germinating in each petri dish and at the end of experiment, the length and width of the thallus derived from each gemmae were measured. For greenhouse experiment, the mulch extracts were applied to nursery containers filled with standard substrate and amended with controlled-release fertilizer for assessing the postemergent liverwort control in nursery containers. Either RH, HW, CH, ML, SC or PB mulch extracts were applied to each of the container uniformly at either 1X (15ml), 2X (30ml), 3X (45ml), and 4X (60ml) rates, at the beginning of experiment and bi-weekly until 10 weeks. Control set without any mulch extract was included as well. Percent of substrate surface covered by liverwort thalli was visually estimated bi-weekly until 10 weeks after first treatment. Fresh biomass of the thalli and number of gemmae cups in each pot were also recorded at the end of the experiment. Both lab and greenhouse experiments had four replications per treatment and were arranged in a randomized complete block design. After 1 week in the growth chamber, ML followed by SC, PB and RH extracts showed maximum suppression of liverwort gemmae germination. At 2 weeks, all rates of ML provided complete inhibition of liverwort. In the greenhouse, all the mulch extracts were able to provide complete liverwort control for the first two weeks. PB and HW mulches showed excellent liverwort control and minimum biomass of liverwort after 10 weeks as compared to other mulches. Hence, the allelopathic potential of the organic mulches can be a promising option for biopesticidal control of liverwort, and a component of integrated liverwort management.

Preemergent herbicides are commonly applied to control many annual weed species in turfgrass systems. Oxadiazon and prodiamine are pre-emergent herbicides that effectively inhibit the growth of emerging annual grasses and broadleaf weeds without harming certain turfgrass species. However, in recent years, a decline in the efficacy of oxadiazon and prodiamine has been observed by golf course managers, leading to an increase in application rates in an attempt to mitigate the issue. Therefore, the objective of this study was to characterize degradation processes that affect oxadiazon and prodiamine persistence and efficacy in order to identify solutions or mitigation strategies. Soil samples were collected from unique sites throughout North Carolina. Field studies were organized as a randomized complete block design containing 3 replications and 2 experimental runs. Treatments were arranged in a split-split plot design, where the whole plots consisted of 4 sites with histories of continuous oxadiazon or prodiamine use (never applied, applied 1-2 years, ~7 years, > 15 years), the sub-plots were 2 treatments (non-sterilized and sterilized), and the sub-sub-plots were 6 collection timings (14, 28, 42, 56, 112, and 168 days after treatment). Herbicide residue quantifications were determined using high-performance liquid chromatography. Data were recorded and converted into a percentage of the applied rate. A higher percent of oxadiazon was observed for sterilized soil (79.2%) compared to non-sterilized soil (73.7%). In the non-sterilized soil, at 14 DAT there were no differences between periods of use. However, at 28 DAT, the soil with no use history presented a higher percentage of oxadiazon (83.0%) compared to 1 and 15 years (75.5%, and 77.1% respectively). Furthermore, at 42 and 56 DAT, the soil with no history of application exhibited the highest percentage of oxadiazon among all periods of use. Findings of this study suggest that there is higher concentration of oxadiazon, meaning less degradation, in the soils with no history of application.

Evaluating Bacterial Diversity and Pest Control Efficacy of Steam Disinfestation Treatments in the Salinas Valley Spinach and Lettuce Fields - Erika Escalona
Development of Minirhizotron for Nondestructive Rapid Detection of Parasitic Nematodes - Tim Pannkuk
Genome Sequencing of Crapemyrtle Bark Scale for Developing Advanced IPM Strategies - Bin Wu
A New Technique for Visual and Quantitative Assessment of Pesticide Applications to Tree Trunks for Control of Trunk-boring Insects - Amy Fulcher
Factors Affecting Spray Coverage on Red Maple Trunks from an Air-Assisted Sprayer - Amy Fulcher
Rice Hull Use in Container Production; Economics and Efficacy - Shawn Steed
Organic and Synthetic Herbicides for Controlling Liverwort Growth in Containerized Ornamental Production - Manjot Sidhu
Impact of Changing Climate on Weed Control in Ornamental Crop Production: A Potential Research Area - Supti Saha Mou
Development of “EZA”, a New Pesticide Suitable for Organic Production of Horticultural Crops - Merci Uwimbabazi
Impact of Partial Saltwater Agroecosystems on Weed Competition in Watermelon. - Joseph Bazzle

As the threat of climate change intensifies, the need for sustainable and environmentally friendly pest and pathogen control methods in agriculture becomes increasingly urgent. Steam disinfestation, a method once considered outdated and replaced by chemical pesticides, is experiencing a resurgence due to heightened environmental concerns. Despite its historical use, there has been little exploration of scaling up steam disinfestation for field applications in vegetable crops.
This project focuses on evaluating the effectiveness of band steaming as a disinfestation method in lettuce fields in the Salinas Valley. The study is divided into two parts: the first part assesses pest control, while the second part examines the impact of band steaming on the soil microbiome.
Our goal is to validate band steaming as a viable alternative to chemical pesticides through a thorough assessment in agricultural fields. The experiment was conducted during 2023 trials at Hartnell’s USDA research facility in Salinas, CA, using a custom-built steam applicator with a 1,000 kg/hour low-pressure steam generator. Pest control analysis focused on Pythium spp., a soil-borne disease, and weed emergence, with disease assessment carried out through pathogen assays in soil samples. Additionally, we examined the impact of band steaming on the soil microbiome using 16S sequencing, collecting soil samples before, one day after, and 30 days after steam treatment.
Preliminary results show effective weed control and reduced pathogen pressure following steam treatments. Soil microbial analysis indicates that steam treatment influences changes in the soil microbiome, with some recovery in alpha, beta, and functional diversity observed within 30 days. Through a comprehensive assessment of pest control and soil microbial changes, we aim to provide detailed insights into the effectiveness of steam disinfestation and its potential for sustainable agricultural practices.

Plant-parasitic nematodes are a historic problem in a wide range of horticultural and agronomic production conditions. Many horticultural crops can be negatively impacted during production since near-ideal environmental conditions are created for nematode growth and reproduction. Once established in the soil of a nursery, orchard, or greenhouse, there is also potential to spread the plant damaging nematodes via machinery, handheld equipment, soil movement, or footwear. Nematode presence may be detected by root visual symptoms of infected plants, but laboratory nematode assays are a more reliable diagnostic tool – however costly and time consuming. Our team developed a portable handheld infrared thermography-minirhizotron device for rapid, nondestructive detection of the presence or absence of plant parasitic nematodes. This self-contained device, using infrared thermography, processes images using an algorithm. It can be operated by trained personnel to perform on-site rapid diagnosis in a nursery environment. A prototype has been constructed and tested in laboratory setting. It is equipped with wireless communication and network capabilities, allowing remote access and control. The goal is to develop a smart device that can be scaled up and networked for early detection and rapid response to a wide range of soil nematodes of horticultural importance. The algorithm is developed to distinguish between root-knot and cyst nematodes in infected plants.

Crapemyrtle bark scale (CMBS; Acanthococcus lagerstroemiae), an invasive insect pest threatening horticultural industries, has spurred the search for sustainable control methods. Our recent research focused on two key aspects of CMBS behavior: feeding and mating. In feeding, our studies revealed that while nicotine does not affect the phloem salivation process in CMBS, it significantly impairs the insect’s ability to ingest phloem sap, suggesting that nicotine interferes with the precise muscular coordination in the acephalothoracia region of CMBS, thereby offering a potential mechanism for chemical control. By identifying the genes that encode nicotinic receptors, we can pinpoint potential chemical targets to disrupt CMBS feeding behavior. In studying mating behavior, we found that mating is crucial for CMBS reproduction. Solid-phase micro-extraction and GC/MS assays revealed that CMBS release unique volatile compounds at different life stages. By identifying the genes responsible for sex pheromone production and pheromone receptors, our research lays the groundwork for developing pheromone-based traps and mating disruption strategies. Moreover, the discovery of juvenile hormone receptors and their expression at various developmental stages suggests additional opportunities to hinder CMBS growth and reproduction. We are conducting a comprehensive genomic analysis of CMBS using PacBio SMRT, Hi-C, and Illumina genome sequencing. This genomic framework will be used to develop innovative pest control strategies to control CMBS populations while supporting integrated pest management (IPM) techniques and reducing environmental impact.

Water sensitive paper (WSP), a yellow paper that stains blue in the presence of water, can be used to evaluate spray characteristics. While traditionally used as 2x3-inch cards placed in the canopy, we developed a WSP wrap that can be wrapped around a trunk, sprayed, and removed without damaging the trunk to assess spray distribution for control of trunk-boring insects. Trunk wraps are made by adhering a 1x8.5-inch strip of WSP to a 1.75x8.5-inch strip from a printable vinyl sticker sheet. To install, the adhesive is exposed, the wrap is manually wrapped around the trunk, and pressure is applied by gripping the wrapped portion of the trunk. However, the tapered shape, bumpy surface, and small trunk caliper, as well as humidity can cause wraps to unravel during experiments. In preliminary tests, 50% of uncoiled, i.e., flat, 4.25-inch wraps unraveled from 16.5 mm caliper Acer rubrum ‘Franksred’ Red Sunset® red maple trunks. Our objective was to test if pre-coiling wraps prevented unraveling. We tested four treatments with five replications each: 1. 8.5-inch wraps coiled and stored in 2-inch diameter PVC, 2. 8.5-inch uncoiled wraps, 3. 4.25-inch wraps coiled and stored in 0.75-inch PVC, and 4. 4.25-inch wraps coiled in 0.75-inch PVC and stored in 1-inch PVC. After 2 weeks of storage, we installed wraps on 16.5 mm caliper Red Sunset® trunks. After 5-10 minutes, we reapplied pressure to both 8.5-inch wraps and 4.25-inch flat wraps because they unraveled, our standard practice; both 4.25-inch pre-coiled wrap treatments remained tightly wrapped and did not require this step. After an additional 5-10 minutes we assessed whether or not wraps were tightly wrapped around trunks. All wraps within both 4.25-inch pre-coiled wrap treatments remained tightly wrapped around trunks. All 8.5-inch uncoiled wraps unraveled and 40% of 8.5-inch pre-coiled wraps unraveled suggesting a modest benefit to coiling this length and that extra length is not beneficial. Following this experiment, we successfully used pre-coiled 4.25-inch wraps on 16-19 mm caliper maple and 8.5-inch wraps on 46-52 mm caliper oak tree trunks. We observed that repeated wrap installation (approx. ≥5 times) to the same location on the same day sometimes caused minor bark damage. Pre-coiled wraps of the correct length unraveled in the high humidity of day-time field experiments but remained tightly wrapped in evening trials under less humid conditions. To maintain the coil during storage, we protected wraps with paper, then secured them with a rubber band.

Trunk-boring pests are a significant threat to nursery crops. Despite the prominence of air-assisted sprayers, little research has been published about their coverage of tree trunks. We assessed spray characteristics of a Jacto A400/850 sprayer with the objective of determining the lowest spray rate that provided at or near 100% trunk coverage. Water sensitive paper (WSP) was wrapped around the trunks at two heights in an external row and the middle row of a 3-row block of red maples (Acer rubrum) to assess coverage. Assessments included 15 trials with application rates from 65 to 244 GPA at 1.5 and 2.5 mph tractor speeds. Travel Speed: Spraying at 108 GPA and 112 GPA achieved ≥95% coverage when traveling 1.5 mph with windspeeds less than 1.5 mph. Spraying 112 GPA at 1.5 mph provided 96% coverage on wraps at both heights despite a maximum (unsustained) windspeed of 3.9 mph. Increasing the travel speed to 2.5 mph reduced the spray rate to 68 GPA and coverage to 79%. Spraying 244 GPA when traveling 1.5 mph provided 95% coverage. Increasing the travel speed to 2.5 mph decreased the rate to 146 GPA, and yielded coverage of 97%. Spraying 146-224 GPA with 1.0 mph average windspeed or less yielded ≥95% coverage in all four trials. Wind Speed: When traveling 1.5 mph and spraying 108 GPA with an average windspeed of 1.3 mph, 96% coverage was achieved. Coverage was reduced to 88% when the average windspeed increased to 2.5 mph. Stakes: Trees were secured using 1-inch stakes installed 3 inches from the western face of each trunk. The western face of wraps at 9 of 12 locations had coverage equal to or greater than that of the total wrap in three trials with less than 1.3 mph average windspeed. Row: In 10 trials, there was ≤2.5% difference in coverage between external and middle rows. However, in 5 trials the middle row had greater coverage by at least 6%. Spraying 109-112 GPA can provide near complete trunk coverage under low wind speeds. Higher spray rates can overcome high wind and travel speed, but are undesirable given the potential for drift and waste. Neither presence of a stake nor middle row position equates to worse coverage. Trees in the middle row may benefit from being equidistant from the sprayer as it travels down both driveways. These results provide a framework for future trunk coverage tests utilizing variable-rate technology.

Weed control in woody ornamental container production is one of the most expensive inputs in production. Preemergent herbicides, mulches and hand labor are all methods of delaying, impeding, or removing weeds that will negatively impact the growth and aesthetics of the produced container plant. One method gaining popularity in Central Florida to reduce weed competition is the use of rice hulls (RH) as a mulch. Effective mulches will reduce the amount of weed competition plants face. Rice hulls are a byproduct from the rice industry and deemed a disposed waste. RH are applied by hand in a layer of about 0.5 to 1 inch deep and dry out in a relatively quick manner. Growers anticipate that RH reduce the costs of weed competition and hand labor from weeding operations. This research investigated the economic cost of RH and benefit of RH mulch in terms of weed growth reduction.

Liverwort (Marchantia polymorpha L.) is a nonvascular, chlorophyll-containing, primitive, spore-bearing bryophyte. It is one of the major weed problems in container nurseries and greenhouse operations as it competes with the ornamental plant for resources within the container. Application of herbicides is a major component of any weed control program in ornamental production systems. There are limited herbicides labeled for liverwort control in greenhouse container production. A greenhouse experiment was conducted to evaluate the effect of various organic and synthetic herbicides on controlling liverwort growth. The herbicides were applied to nursery containers filled with standard substrate and amended with controlled release fertilizer for assessing the post-emergent liverwort control. Organic products namely Avenger, Scythe and WeedPharm were applied at 1X and 2X rates. Synthetic herbicides – Glyphosate, 2,4-D and Indaziflam were applied at 1X, 2X and 3X rates. Control set without any herbicide application was included as well. Percent of substrate surface covered by liverwort thalli was visually estimated bi-weekly until 16 weeks after first treatment. Fresh biomass of the thalli in each pot were also recorded at the end of the experiment. The experiment had six replications per treatment, and they were arranged in a randomized complete block design. For both the synthetic and organic herbicides, there was significant interaction between the type and rate of herbicide applied. The herbicide treatments were significantly different amongst each other and from the control. Out of various organic herbicides applied, all the herbicide treatments were able to limit liverwort coverage under 30% as compared to control (98%). WeedPharm and Scythe application at 2X and Avenger application at 1X rates recorded minimum liverwort fresh biomass. In the synthetic herbicide treatments, Indaziflam at 2X and 3X rates had minimal liverwort coverage and fresh biomass at the end of the experiment. Hence, these organic and synthetic herbicides can be a promising component for an integrated liverwort control program in containerized ornamental production.

The ornamental crop industry is a billion-dollar industry in the United States. Controlling weeds is a big challenge, as they can compete with ornamentals for soil, nutrients, water, light, and space by affecting the desired quality of ornamental crops like leaf and flower quality and color as well as proper growth. Weeds can also harbor insects, pests, diseases, and pathogens resulting in further reduction of market value. Due to greater genetic diversity and physiological plasticity, weeds are more likely to be able to adapt to a changing environment or climate. Increased atmospheric carbon dioxide (CO2) level can cause fertilization effect in C3 plants resulting in higher growth rates. Conversely, C4 plants are less likely to exhibit increased growth responses to elevated CO2 levels, as carbon dioxide fixation becomes saturated for them at around 360 ppm. So, ornamentals could gain a competitive advantage over many of the major weed species under elevated CO2, as many of the world’s ornamental crop species are C3 plants and many of the major weed species are C4 plants. But in reality, the scenario is different because other factors such as changes in herbicide efficacy and the ability of weed species to out compete ornamental species may come into play and limit this advantage. Plants that are grown in CO2-enriched environments often develop high concentrations of starch in leaves and greater total leaf area and biomass which can cause a dilution effect on herbicides. Additionally, C3 plants have been shown to have decreased stomatal conductance and increased leaf thickness in elevated CO2 which may also limit foliar uptake of herbicides. Environmental factors such as temperature, precipitation and relative humidity influence the efficacy of herbicides. There are studies that have reported decreased herbicide efficacy for control of annual and perennial weeds in elevated CO2 environments in agronomic crops. But limited information is available on how change in climate can affect herbicide efficacies in ornamental production. Hence, the objectives of this research proposal are: Evaluating increased temperature and CO2 levels on growth and reproduction of two different types of container-grown ornamentals; Determining effects of temperature and CO2 rise on preemergence herbicide performances for controlling C3 and C4 weed species; Determining effects of temperature and CO2 rise on postemergence herbicide performances for controlling C3 and C4 weed species; Assessing adaptive features of weed species with the change in environmental factors.

Production of economically important horticultural crops in the world, especially in developing countries, is faced with major challenges, including pests, and diseases. As a result, producers rely heavily on excessive use of synthetic pesticides, which often leads to negative impact to the environment, human health, and pesticide resistance. There is a need to develop environmentally friendly products to manage pests and diseases to increase crop yield, quality, and nutrition. Research was conducted in Rwanda to develop “EZA”, a new pesticide acting as an insect repellent, made of essential oils from local invasive plants such as Lantana camara, Tagetes minuta, and wastes of chili pepper and garlic. EZA was tested on tomatoes and mangoes under field conditions to manage several insect pests, including armyworms, fruit flies, thrips, and diseases such as tomato late blight caused by Phytophthora infestans. Results showed that EZA was effective in controlling insect pests, providing control of thrips and tomato late blight at the rate of 90% on 5 tomato plants where applied. Furthermore, tomato yield was increased by 40%. Information from this study demonstrates that EZA could significantly benefit horticultural crop producers, especially smallholder farmers in developing countries such as Rwanda, to effectively manage insect pests and diseases and the increase of crop yield.

The issue of soil salinity as a major cause of poor soil health and crop yield loss has been of growing concern as climate change contributes to its effects. The objective of this research was to study the impact of increasingly saline soils on the relationship between grafted watermelons and yellow nutsedge, one of the major weeds in watermelon plasticulture. The seedless watermelon cultivar Melody was grown in a field after being grafted onto the C. maxima hybrid Carnivor and the C. amarus cultivar Carolina Strongback in addition to both a self-grafted and ungrafted control. The field was divided into four rows, which were irrigated with 0, 10%, 20%, and 30% dilutions of sea water for the duration of the experiment. A weed count was performed after one month and three months of irrigation. This demonstrated that salt had a significant effect on the total weed count at high concentrations, however the weeds demonstrated a much greater resistance to salt treatment than the watermelons in this trial. Based on this data, it is possible that salt intrusion events can contribute to increased weed related yield loss in watermelon crops.