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Preemergence (PRE) herbicides are used to control weeds and reduce pressure on postemergence (POST) herbicides. However, knowledge of length of control each herbicide provides, as well as the amount of activation rainfall required for adequate weed control, is unknown in Mississippi soybean production. Twenty-one PRE applied soybean herbicides were evaluated for their duration of residual control for five weeks over twelve site years on three weed species from 2021-2022. Some differences in control following herbicide application used on certain weed species were observed at different times. However, most PRE herbicides resulted in adequate (greater than or equal to 90%) control of weed species evaluated up to 35 days after emergence. Also, four PRE herbicides were evaluated in the greenhouse to quantify the amount of rainfall needed for activation when applied to three different soil textures. These data suggest that rainfall recommendations vary by herbicide and soil texture, and some herbicides were effective at controlling weed species at low rainfall amounts (less than 12.7mm).

Herbicide resistance development among weed populations in cotton and peanut is becoming increasingly difficult to manage. If resistant populations continue to persist, weed control practices for producers will become less efficient and more costly. The objective of this research was to evaluate alternative weed control techniques designed to mitigate herbicide resistance development for their agronomic and economic impact on weed management systems. Studies were conducted in 2019, 2020, and 2021 at multiple locations in Mississippi and Arkansas investigating multiple techniques including the addition of soil surfactants in herbicide tank mixtures, increasing SOAs utilized in peanut herbicide programs, applying non-labeled herbicides to cotton with post-directed spray placement, and applying complete residual herbicide programs in cotton. Our results suggests that some novel strategies incorporated into existing weed management programs, can provide sufficient control of troublesome weed species and conserve crop yield and profit returns. For example, the use of post-directed application placement allowed for non-labeled herbicides to be applied to cotton without detrimental effects, thus increasing potential options for POST weed control within that crop. Additionally, weed control, seed cotton yield, and net returns were not affected when only residual herbicides were applied in season-long weed control programs as opposed to the standard of mixed, foliar and residual programs. This indicates that high selection pressure associated with foliar chemistries which leads to resistance development, can be alleviated through the adoption of alternative strategies.

Harvest weed seed controls (HWSC) destroy weed seeds that are retained by the plant at crop harvest, which would typically be spread by the harvester along with other field residues. HWSC exploits coincidental maturity between crops and weeds, so an experiment was designed to collect weed seeds as they shatter throughout the growing season and through a simulated harvest delay. This experiment monitored four economically important broadleaf species and two grass species in a soybean (Glycine max (L.) Merr.) field. Results indicated that broadleaf species shattered seed at rates accelerating through the growing season, while grass species shattered more seed early in the growing season. Field experiments in organic and conventional winter wheat (Triticum aestivum L.) fields infested with Italian ryegrass (Lolium perenne L. ssp. multiflorum (Lam.) Husnot) compared two HWSC techniques to grower-standard weed management programs in each system, including both no-till and full-till standard treatments in the conventional system. Italian ryegrass populations were monitored, and wheat yield was measured both before and after HWSC application. In both organic and conventional cropping systems, HWSC treatments did not provide better Italian ryegrass control than the grower-standard treatments. The conventional program including tillage boosted Italian ryegrass populations. These results suggest that HWSC treatments did not enhance Italian ryegrass control compared to grower-standard practices in either the organic or conventional systems. Additionally, broadleaf weeds may retain enough seeds to be viable targets for HWSC. Incorporating best practices, such as a timely crop harvest, is key for understanding and optimizing HWSC. / Master of Science / Harvest weed seed controls (HWSC) destroy weed seeds that the weed plant retains at the time of crop harvest. On a typical farm, these weed seeds pass through the crop harvester and get spread across the field along with other plant materials. HWSC directly targets weed seeds, differentiating itself from normal weed management practices, such as herbicides, that kill emerging or emerged weed plants. With HWSC, weed seeds never enter the soil seed bank, thus depleting weed populations over time. HWSC works through mechanical means, such as crushing, burning, or removal. For conventional farmers battling herbicide resistant weeds, HWSC can provide effective weed management by diversifying weed management programs. HWSC also has promise as a new chemical-free weed management for organic farmers. HWSC relies on crops and weeds having coincidental maturity; seeds released from the plant (shattered) before crop harvest cannot be targeted by HWSC. An experiment was designed to collect weed seeds weekly as they shatter throughout the growing season, continuing until three weeks after the ideal date to harvest crops, thereby simulating a situation where weather or logistical factors prevented a timely crop harvest. This experiment monitored four broadleaf species and two grass species that infest soybean fields. Broadleaf species shattered seeds at increasing rates throughout the soybean growing season, with each species shattering over 50% of captured seed during the simulated harvest delay. Compared to broadleaf weeds, grass species shattered relatively more seed early in the growing season. This experiment indicates that broadleaf weeds may be more suited to control by HWSC. HWSC was also used in organic and conventional winter wheat fields infested with Italian ryegrass. These experiments compared two HWSC techniques, windrow burning of field residue and residue removal to standard weed management programs in each system. Windrow burning incinerates field residues, eliminating weed seeds within. Residue removal takes all field residues off the field for disposal elsewhere. While the standard organic weed management program involved tillage by default, the conventional cropping system featured both no-till and full-till standard weed management programs. Italian ryegrass populations were monitored through population counts, biomass collections, and counting of seed remaining at harvest. Wheat yield was also recorded. These measurements were taken both before HWSC application and after the first year of HWSC, to compare year-to-year changes. In the organic cropping system, Italian ryegrass populations grew and wheat yield decreased at similar rates for both HWSC treatments and the standard weed management program. In the conventional cropping system, Italian ryegrass populations declined and wheat yield increased for HWSC and the no-till standard treatments. Tillage, however, boosted Italian ryegrass populations, keeping them at similar levels to the previous growing season. These results suggest that HWSC treatments did not enhance Italian ryegrass control compared to standard practices in either the organic or no-till conventional systems. Though these results indicate that broadleaf weeds may retain enough seeds to be viable targets for HWSC, more research is needed to optimize HWSC for Italian ryegrass control, especially for organic growers. Incorporating best agricultural practices, such as a timely crop harvest, is key for improving HWSC’s efficacy. Commercial implementation of HWSC depends on further understanding of how specific HWSC practices, such as windrow burning, interact with the agricultural landscape, including effects on landscape aesthetics and soil nutrition. HWSC holds promise for diversifying weed management and limiting reliance on herbicides, but its true potential is yet to be revealed.

Effective weed control is crucial, especially for herbicide-resistant species. Machine vision technology, through weed detection and localization, can facilitate precise, species-specific treatments. Despite the challenges posed by unstructured field conditions and weed variability, deep learning (DL) algorithms show promise. This study evaluated thirteen DL-based weed detection models, including YOLOv5, RetinaNet, EfficientDet, Fast RCNN, and Faster RCNN, using pre-trained object detectors. RetinaNet (R101-FPN) achieved the highest accuracy with a mean average precision (mAP@0.50) of 79.98%, though it had longer inference times. YOLOv5n, with the fastest inference (17 ms on Google Colab) and only 1.8 million parameters, achieved a comparable 76.58% mAP@0.50, making it suitable for real-time use in resource-limited devices. A prototype using YOLOv5 was tested on two datasets, showing good real-time accuracy on In-season data and comparable results on Cross-season data, despite some accuracy challenges due to dataset distribution shifts.

Call number: LD2668 .T4 1952 S93 / Master of Science

Doctor of Philosophy / Department of Agronomy / Johanna A. Dille / Challenges in weed management include occurrence of multiple weed species in the field, variable emergence among weed species, different spatial distribution and weed densities, which leads to the persistence of weed patches. The overall objective of this research was to understand the interaction of weed emergence, weed density, herbicide choice, and herbicide rate in soybean. Specific objectives were 1) to characterize the seedbank and emergence patterns of shattercane (Sorghum bicolor L.), prickly sida (Sida spinosa L.), and ivyleaf morningglory (Ipomoea hederacea Jacq.) including initial, peak, end, and duration of emergence in response to crop and herbicide treatments in soybean, and 2) to evaluate large crabgrass (Digitaria sanguinalis L.), shattercane, Palmer amaranth (Amaranthus palmeri S.), and velvetleaf (Abutilon theophrasti Medik.) mortality and dry weight reduction in response to herbicide rates across varying weed densities as well as to determine the influence of velvetleaf growth stage and density on herbicide efficacy. In the emergence study of 2006 to 2008, four treatments were nocrop, no-residual herbicide, half-rate of residual herbicide and full-rate of residual herbicide. Reduction in weed emergence was observed over the years in the same species patch. Species emerged in mid-May in both years, coinciding with soybean planting. Extended emergence was observed for shattercane when moisture was low and temperature high, while for prickly sida and ivyleaf morningglory, extended emergence was observed when moisture was high and temperature low. Applying residual herbicide decreased weed emergence. Herbicide choice was the whole plot, herbicide rates were subplots and weed densities were sub-subplots in field experiments conducted in 2006 and 2007. Shattercane was more susceptible to both glyphosate and clethodim than large crabgrass. Increasing large crabgrass density reduced percent mortality with clethodim, while with glyphosate, density did not affect both species mortality. Shattercane dry weight was reduced to 0 g per plot with 0.1X labeled rate of clethodim or glyphosate while 0.5X of the labeled rate reduced dry weight of large crabgrass to 0 g per plot. For broadleaf weeds, higher percent mortality was observed with glyphosate than with lactofen at high densities. Palmer amaranth was more susceptible than velvetleaf. Velvetleaf response was density dependent, such that increasing density did not increase dry weight. Velvetleaf growth stage was of importance, as stage affected herbicide efficacy, with higher mortality achieved at the two-leaf stage than the four- and six-leaf stages. For glyphosate, 0.125X of labeled rate on velvetleaf density of 5 seedlings per pot achieved more than 90% mortality when applied at the two-leaf stage, but dropped to 60 and 50% mortality when applied at the four- and six-leaf stage, respectively. The trend was the same for velvetleaf at a density of 30 seedlings per pot, which had 80, 60, and 55% mortality for the two-, four-, and six-leaf stages, respectively. Weed managers and farmers have the opportunity to better select herbicide choice and rate based on weed species, weed emergence patterns, and weed density.

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3 pp. / Revised / Weeds can be a problem in wheat and barley especially where crop rotation is not practiced. An integrated approach to weed management can be followed. Chemical treatments are important tools in weed management to maintain yield and quality and prevent proliferation of weeds that could affect future crops.

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