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This research uncovers a novel pathway in precision agriculture, emphasizing the utilization of advanced supervised and self-supervised deep learning approaches for an innovative solution to weed detection and crop yield prediction. The study focuses on key weed species: Italian ryegrass in wheat, Palmer amaranth, and common ragweed in soybean, which are troublesome weeds in the United States. One of the most innovative components of this research is the debut of a self-supervised learning approach specifically tailored for soybean yield prediction using only unlabeled RGB images. This novel strategy presents a departure from traditional yield prediction methods that consider multiple variables, thus offering a more streamlined and efficient methodology that presents a significant contribution to the field. To address the monitoring of Italian ryegrass in wheat cultivation, a bespoke Convolutional Neural Network (CNN) model was developed. It demonstrated impressive precision and recall rates of 100% and 97.5% respectively, in accurately classifying Italian ryegrass in the wheat. Among three hyperparameter tuning methods, Bayesian optimization emerges as the most efficient, delivering optimal results in just 10 iterations, contrasting with 723 and 304 iterations required for grid search and random search respectively. Further, this study examines the performance of various classification and object detection algorithms on Unmanned Aerial Systems (UAS)-acquired images at different growth stages of soybean and Palmer amaranth. Both the Vision Transformer and EfficientNetB0 models display promising test accuracies of 97.69% and 93.26% respectively. However, considering a balance between speed and accuracy, YOLOv6s emerged as the most suitable object detection model for real-time deployment, achieving an 82.6% mean average precision (mAP) at an average inference speed of 8.28 milliseconds. Furthermore, a self-supervised contrastive learning approach was introduced for automating the labeling of Palmer amaranth and soybean. This method achieved a notable 98.5% test accuracy, indicating the potential for cost-efficient data acquisition and labeling to advance precision agriculture research. A separate study was conducted to detect common ragweed in soybean crops and the prediction of soybean yield impacted by varying weed densities. The Vision Transformer and MLP-Mixer models achieve test accuracies of 97.95% and 96.92% for weed detection, with YOLOv6 outperforming YOLOv5, attaining an mAP of 81.5% at an average inference speed of 7.05 milliseconds. Self-supervised learning-based yield prediction models reach a coefficient of determination of up to 0.80 and a correlation coefficient of 0.88 between predicted and actual yield. In conclusion, this research elucidates the transformative potential of self-supervised and supervised deep learning techniques in revolutionizing weed detection and crop yield prediction practices. Its findings significantly contribute to precision agriculture, paving the way for efficient and cost-effective site-specific weed management strategies. This, in turn, promotes reduced environmental impact and enhances the economic sustainability of farming operations. / Master of Science in Life Sciences / This novel research provides a fresh approach to overcoming some of the biggest challenges in modern agriculture by leveraging the power of advanced artificial intelligence (AI) techniques. The study targets key disruptive weed species, such as, Italian ryegrass in wheat, Palmer amaranth, and common ragweed in soybean, all of which have the potential to significantly reduce crop yields. The studies were first conducted to detect Italian ryegrass in wheat crops, utilizing RGB images. A model is built using a complex AI system called a Convolutional Neural Network (CNN) to detect this weed with remarkable accuracy. The study then delves into the use of drones to take pictures of different growth stages of soybean and Palmer amaranth plants. These images were then analyzed by various AI models to assess their ability to accurately identify the plants. The results show some promising findings, with one model being quick and accurate enough to be potentially used in real-time applications. The most important part of this research is the application of self-supervised learning, which learns to label Palmer amaranth and soybean plants on its own. This novel method achieved impressive test accuracy, suggesting a future where data collection and labeling could be done more cost-effectively. In another related study, we detected common ragweed in soybean crops and predicted soybean yield based on various weed densities. AI models once again performed well for weed detection and yield prediction tasks, with self-supervised models showcasing high agreement between predicted and actual yields. In conclusion, this research showcases the exciting potential of self-teaching and supervised AI in transforming the way we detect weeds and predict crop yields. These findings could potentially lead to more efficient and cost-effective ways of managing weeds at specific sites. This could have a positive impact on the environment and improve the economic sustainability of farming operations, paving the way for a greener future.

Early planting soybean (Glycine max L.) strategies across the mid-southern United States has complicated weed management in the form of post-harvest weed control. Research has investigated the use of cover crops to aid in management of weed populations during winter months, but conventional cover crops provides minimal weed management benefit immediately following cash crop harvest. Inter-seeding cover crop into crop canopies has potential to promote earlier cover crop establishment, thus creating higher potential for post-harvest weed management. However, factors such as inter-seeding timing, herbicide residue, as well as harvest aid applications must be considered. Therefore, studies were conducted in Mississippi in 2017, 2018, and 2019 to determine if cover crops inter-seeded through soybean could improve weed control used in conjunction with common management strategies in Mississippi production systems. Conclusions drawn from these studies indicate inter-seeded cover crops can be utilized in soybean production systems to improve weed management after harvest.

Studies were conducted in the field from 2018-2019 in peanut to optimize weed control through application methods and herbicide choices. The herbicide studies were established in Mississippi, Oklahoma, Florida, and Alabama. Across trials, programs that included imazapic POST improved weed control at 28 days after treatment (DAT). The most effective PRE herbicides were flumioxazin, diclosulam, and S-metolachlor, while the use of pendimethalin was less effective. Various nozzles and operating pressures were evaluated for weed control in peanut. Droplet size was measured for each of the nozzles used at all operating pressures tested to determine classification. Classification was determined using the ASABE S572.2 standard. There was no effect on weed control or yield based on nozzle type or application pressure.

Field experiments were conducted in Virginia to evaluate the efficacy of AEF-130060 03 plus AEF-107892 applied postemergence (POST) for the control of Italian ryegrass [Lolium multiflorum (Lam)] in barley [Hordeum vulgare (L.)] in comparison to other herbicides currently registered for use in wheat [Triticum aestivum (L.)] and barley. Laboratory experiments were also conducted to evaluate absorption, translocation and metabolism of AEF-130060 03 plus AEF-107892 in wheat, barley, and Italian ryegrass with or without the addition of dicamba. AEF-130060 03 plus AEF-107892 was applied alone at three POST timings. All of these applications were effective in controlling Italian ryegrass. The third application timing of AEF-130060 03 plus AEF-107892 commonly resulted in lower yields than the first or second application timing, due to increased duration of Italian ryegrass competition, increased barley injury and insufficient time for barley recovery from this injury. In the field experiment, significantly greater barley injury was observed when AEF-130060 03 plus AEF-107892 was combined with 2,4-D and dicamba. Early postemergence (EP) treatments of AEF-130060 03 plus AEF-107892 provided control of Italian ryegrass equivalent to that of delayed preemergence (DPRE) applications of flufenacet plus metribuzin when rainfall was received. However, when rainfall was not received AEF-130060 03 plus AEF-107892 provided superior control. Because the efficacy of AEF-130060 03 plus AEF-107892 is not dependant on rainfall, it should provide more consistent control of Italian ryegrass than DP treatments. Laboratory experiments indicated that Italian ryegrass absorbed greater than 2.5, 2.0, and 1.5 times the amount of applied radioactivity at 24, 48, and 96 hours after treatment (HAT), respectively, than wheat or barley. Metabolism experiments indicated that quantity of parent compound in the three species was greatest in Italian ryegrass, followed by barley and then wheat. However, the sum total of metabolites was not different between species. A higher rate of metabolism of AEF-130060 03 plus AEF-107892 was also observed in wheat and barley than in Italian ryegrass. Thus, lower absorption of herbicide by wheat and barley, coupled with a more rapid rate of metabolism, most likely accounts for differential selectivity between these plant species. No differences in absorption, translocation or metabolism were observed within the three plant species due to the addition of dicamba. An additional experiment was conducted in 2000 and 2001 to evaluate the efficacy of preemergence (PRE) and EP applications of DPX-R6447 for the control of Italian ryegrass in wheat and barley in comparison to other herbicides currently registered for use in these crops. Barley and wheat injury and yield were similar with treatments of DPX-R6447 at rates below 176 g ai/ha and treatments of flufenacet plus metribuzin applied alone in both years. Consistent Italian ryegrass control with DPX-R6447 occurred only with rates of 176 g ai/ha or greater in both years. However, these rates resulted in variable injury in both wheat and barley between years. Rates higher than 176 g ai/ha of DPX-R6447 resulted in unacceptable barley and wheat injury. The lack of consistency with regard to barley and wheat injury could limit the utility of this compound in these crops. Field trials were conducted in Virginia to evaluate herbicide programs for control of Italian ryegrass in no-till corn [Zea mays (L.)] establishment. Herbicide programs using transgenic corn hybrids were compared to standard programs that utilize non-selective herbicides in combination with high rates of triazine herbicides. Italian ryegrass control and corn yields similar to those provided by standard programs could be attained through the use of paraquat plus atrazine, and glyphosate applied in combination with atrazine or rimsulfuron plus thifensulfuron-methyl. In glyphosate-tolerant corn, EP applications of glyphosate controlled Italian ryegrass, but yield did not differ from yields of corn treated with standard PRE applications of glyphosate plus atrazine. The use of glufosinate, imazethapyr plus imazapyr, or sethoxydim with appropriate herbicide-tolerant hybrids did not demonstrate potential for improved control of Italian ryegrass. Field experiments were also conducted to investigate the incidence and severity of maize chlorotic dwarf virus (MCDV) and maize dwarf mosaic virus (MDMV) in response to POST johnsongrass control in two corn hybrids. Recent observations have indicated a lack of virus-tolerance in glyphosate-tolerant corn hybrids in Virginia. The rapidity of virus disease development in corn resulting from application of glyphosate or nicosulfuron was also investigated. The virus-susceptible glyphosate-tolerant hybrid developed significantly higher levels of virus incidence three weeks after treatment than the virus-tolerant, non-transgenic hybrid, and virus incidence and severity increased throughout the duration of the growing season. Little or no disease incidence occurred in the virus-tolerant hybrid. The virus-susceptible hybrid exhibited significant increases in disease incidence in response to any herbicide treatment applied to johnsongrass-containing plots relative to the same treatment applied to weed free plots. Johnsongrass control with nicosulfuron or glyphosate caused similar disease incidence and severity in the virus-susceptible hybrid, regardless of application method. Results of these experiments indicated that growers' choice of hybrid should focus primarily on disease resistance rather than herbicide resistance. / Ph. D.

As the importance of cotton (Gossypium hirsutum L.) to Virginia crop growers has increased, so has the need for more efficient weed control programs. Current cotton herbicides do not control all broadleaf weeds over the entire growing season, and many cotton herbicides must be applied at specific growth stages in order to reduce crop injury. CGA 362622 is an experimental sulfonylurea herbicide that controls many broadleaf weeds at low use rates. Field, greenhouse, and laboratory studies were conducted to evaluate the potential benefit of CGA 362622 to Virginia cotton growers. Postemergence applications of CGA 362622 resulted in moderate crop response that proved transient in all instances and did not affect cotton yield. Broadleaf weed control from herbicide combinations with CGA 362622 generally controlled weeds more consistently than individual herbicide applications. Timely applications of CGA 362622 controlled common ragweed (Ambrosia artemisiifolia L.), common lambsquarters (Chenopodium album L.), annual morningglory species (Ipomoea spp.), and common cocklebur (Xanthium strumarium L.). However, CGA 362622 applications generally did not control spurred anoda (Anoda cristata (L.) Schlecht.), jimsonweed (Datura stramonium L.), velvetleaf (Abutilon theophrasti Medicus), or annual grass species, but combination treatments of CGA 362622 plus pyrithiobac did control velvetleaf, spurred anoda, and jimsonweed. Combinations of CGA 362622 plus glyphosate controlled common lambsquarters and smooth pigweed (Amaranthus hybridus L.) better than glyphosate alone, and in most instances controlled annual morningglory species better than glyphosate applied alone. Timely applications of CGA 362622 plus bromoxynil controlled velvetleaf, smooth pigweed, common ragweed, common lambsquarters, and common cocklebur. Spurred anoda control was generally not acceptable from CGA 362622, bromoxynil, or CGA 362622 and bromoxynil combinations. In laboratory studies, results supported differential absorption, translocation, and metabolism as the main factors for differential tolerance of cotton, spurred anoda, and smooth pigweed to CGA 362622. Rapid translocation and a slow rate of metabolism likely explains the susceptibility of smooth pigweed to this herbicide, while reduced absorption and translocation plus rapid metabolism contribute to CGA 362622 tolerance in cotton. Limited translocation may also explain the intermediate tolerance of spurred anoda to the herbicide CGA 362622. / Ph. D.

Mesotrione is the first triketone herbicide registered for use in turfgrass. Triketones prevent carotenoid biosynthesis by inhibiting the enzyme p-hydroxyphenylpyruvate dioxygenase (HPPD). Although mesotrione controls many species of grass and broadleaf weeds, it is best know for selective control of perennial grasses like creeping bentgrass (Agrostis stolonifera L.). Field trials conducted at Virginia Tech and Blacksburg Country Club determined that several programs that integrate herbicide treatment and turf seeding effectively transitioned creeping bentgrass contaminated golf roughs back to a tall fescue [Schedonorus phoenix (Scop.) Holub] monoculture. However, mature weeds require multiple mesotrione applications for effective control. This requirement is a major limitation to mesotrione's competitiveness in turfgrass markets. Several greenhouse and laboratory studies were conducted to evaluate scenarios where mesotrione rates were titrated and applied daily to mimic ascending, descending, and intervallic time-release patterns. These patterns were applied following an initial treatment to foliage or soil to mimic a potential sprayable or granular time-release formulation. These scenarios effectively controlled five targeted weed species equivalent to the standard of two broadcast sprays, regardless of initial application placement or release pattern. However, both time-release treatments and the standard injured tall fescue based on leaf counts, plant weights, and visual phytotoxicity ratings. Additional growth chamber studies found that changes in relative humidity from 50 to 90% caused a 4- to 18-fold increase in plant phytotoxicity with a concomitant decrease in photochemical efficiency when mesotrione was applied to foliage of smooth crabgrass (Digitaria ischaemum (Schreb.) Schreb. ex Muhl.). Furthermore, white tissue was found predominately in the two youngest leaves when mesotrione was applied to soil, but in older leaves when applied only to foliage. Laboratory studies were conducted to evaluate interspecific differences in 14C mesotrione absorption and translocation between two plant species when applied to foliage or roots. Annual bluegrass (Poa annua L.) absorbed 2- to 4-fold more radioactivity than Kentucky bluegrass (Poa pratensis L.). Both species absorbed less radioactivity through roots than through foliage and root absorbed radioactivity was more often exuded into Hoagland's solution while foliar absorbed radioactivity was often found in other foliage. / Ph. D.

Weed control is a critical component in pastures and hayfields in order to ensure maximum forage yields. Typically, broadleaf weed control in pastures and hayfields is achieved through the use of synthetic auxin. However, these herbicides also control desirable broadleaf species such as forage legumes, including white clover. Use of herbicides can lead to severe injury and often complete elimination of white clover, making it difficult for producers to maintain legumes in mixed grass-legume swards while controlling weeds. It is often desirable to have legumes present in the sward due to their high nutritive forage value and ability to fix nitrogen compared to grass only swards. Florpyrauxifen-benzyl + 2,4-D is a new herbicide which is reported to control broadleaf weed species, while preserving white clover. Little published research exists on this herbicide, particularly for use in pastures and hayfields. Research evaluating sward composition indicates that florpyrauxifen-benzyl + 2,4-D is effective in controlling broadleaf weed species while also preserving greater amounts of white clover than any other herbicide treatments. Florpyrauxifen-benzyl + 2,4-D also resulted in significantly more forage grass production than the nontreated control. Florpyrauxifen-benzyl + 2,4-D was less effective than other herbicides when applied via fertilizer impregnation. Additional research assessing the spectrum of broadleaf weed control found that florpyrauxifen-benzyl + 2,4-D is a viable herbicide for the control of several broadleaf weed species including bulbous buttercup, Canada thistle, broadleaf plantain, plumeless thistle, and common ragweed. However, florpyrauxifen-benzyl + 2,4-D was less effective than other herbicides for controlling certain weeds, such as horsenettle. White clover was injured from florpyrauxifen-benzyl + 2,4-D, but was able to fully recover in 90 to 120 days. There were no differences in white clover response between the four varieties tested. When evaluating establishment of forage species, florpyrauxifen-benzyl + 2,4-D did not injure or reduce biomass of tall fescue or orchardgrass plantings, indicating a high level of safety. Florpyrauxifen-benzyl + 2,4-D was also safe to both drilled and frost seeded clover when applied prior to and at planting. Greenhouse trials revealed that flowering white clover is more sensitive to herbicides compared to vegetative white clover, and that safety of white clover to florpyrauxifen-benzyl + 2,4-D is dependent upon use rate. Considerations such as weed species present, and the amount of white clover injury that is considered acceptable will dictate the decision to utilize florpyrauxifen-benzyl + 2,4-D in pastures and hayfields. This research demonstrates the effectiveness and overall utility of florpyrauxifen-benzyl + 2,4-D for use in pastures and hayfields due to the effectiveness of weed species as well as the level of safety to white clover. / Doctor of Philosophy / Pastures and hayfields are a critical component in livestock production. Grazing livestock perform best on highly nutritious forages. Legumes such as white clover are highly nutritious in forage systems and offer other benefits such as the ability to fixate nitrogen. Conversely, weed species negatively impact forage production by competing for resources with desirable forage species. Additionally, many species of broadleaf weeds are toxic to livestock. Because grasses are the backbone of forage systems, the majority of weed control efforts are aimed at controlling broadleaf weed species. However, beneficial forage legumes such as white clover are susceptible to broadleaf herbicides commonly used. This creates a management dilemma for producers who wish to control troublesome weeds, but also have white clover present in their pastures and hayfields. Florpyrauxifen-benzyl + 2,4-D is a herbicide combination which is new for pastures and hayfields. This herbicide is reported to control broadleaf weeds while also preserving white clover. Research trials were conducted in order to determine if florpyrauxifen-benzyl + 2,4-D could be used in forage systems to control weeds, without killing white clover. Several research trials were established to evaluate florpyrauxifen-benzyl + 2,4-D for broadleaf weed control and white clover safety. Research trials were established to determine the effect of florpyrauxifen-benzyl + 2,4-D on the number and overall amount of forage produced and the proportion of weeds and desirable forages as affected by herbicide treatment. Florpyrauxifen-benzyl + 2,4-D resulted in a 140% increase in forage grass production, and more legume production than any other herbicide treatment, while also decreasing the quantity and amount of broadleaf weed species. Because there is little existing research on what weed species florpyrauxifen-benzyl + 2,4-D controls, research trials were established to determine the spectrum of weed species that florpyrauxifen-benzyl + 2,4-D controls. Greenhouse trials were also established to evaluate the effect of white clover variety on injury from herbicide. Results showed that florpyrauxifen-benzyl + 2,4-D is effective in controlling several weeds such as bulbous buttercup, Canada thistle, broadleaf plantain, plumeless thistle, and common ragweed. Greenhouse trials showed that white clover variety did not influence the level of injury from herbicide applications. Seedling forages are more vulnerable to weed competition and therefore weed control around the time of planting is critical. However, seedlings are typically very sensitive to herbicides, compared to mature plants. Research trials were established to determine the effect of florpyrauxifen-benzyl + 2,4-D on the establishment of forage grasses tall fescue and orchardgrass, as well as white clover. White clover was established using two commonly used methods: drilling and frost-seeding. Results from the field show that florpyrauxifen-benzyl + 2,4-D is safe use around the time of tall fescue and orchardgrass establishment, as well as white clover planting with either method. Greenhouse trials were also established to determine if white clover's growth stage at the time of herbicide application influences the response. Results show that white clover is more sensitive to herbicides applied to flowering white clover compared to vegetative growth and the level of injury is dependent upon herbicide rate. Overall, our results demonstrate the utility of florpyrauxifen-benzyl + 2,4-D for forage production by controlling weed species and being safer to white clover than commonly used herbicides.

Master of Science