Advancements in cold tolerance of seeded bermudagrass and introduction of sulfonylurea herbicides have given turf managers new tools. Seedling bermudagrass response to sulfonylurea herbicides applied before or soon after seeding has not been characterized. Field observations have indicated that variability exists among sulfonylurea herbicides used for perennial ryegrass control. Objectives of the conducted research were to evaluate sulfonylurea herbicides for safety and utility while establishing seeded bermudagrass, and to elucidate variability in perennial ryegrass control with foramsulfuron. Field experiments were conducted in Blacksburg, VA to assess turfgrass and smooth crabgrass response to flazasulfuron, foramsulfuron, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron-sodium, applied 1 and 3 weeks after and before seeding. Herbicides applied 3 weeks after seeding (WAS) were generally more injurious than when applied 1 WAS. Foramsulfuron, metsulfuron, and sulfosulfuron are safe to apply 1 and 3 WAS, causing no reduction in turf cover. Herbicides applied before or after seeding injured bermudagrass in the following order from most to least injurious: flazasulfuron = trifloxysulfuron > rimsulfuron > metsulfuron = sulfosulfuron > foramsulfuron. Flazasulfuron and trifloxysulfuron-sodium are not safe to use within 3 weeks of seeding, while foramsulfuron and metsulfuron can be used anytime before or after seeding bermudagrass. Flazasulfuron, foramsulfuron, and trifloxysulfuron-sodium were evaluated for perennial ryegrass control as affected by environment. Among environmental variables collected soil temperature averaged 7 DAT correlated best with perennial ryegrass response of the three tested products. Soil temperatures below 18 C perennial ryegrass reduced control 9 WAT from 78 to 31% for foramsulfuron while flazasulfuron and trifloxysulfuron-sodium efficacy were not significantly affected. Temperature dependence on perennial ryegrass control can be ranked from most to least as follows; foramsulfuron > trifloxysulfuron-sodium > flazasulfuron. Studies were conducted to determine absorption and translocation of 14C flazasulfuron when applied to perennial ryegrass roots or foliage. Roots treated with 14C flazasulfuron absorbed 41% of recovered 14C while 25% of 14C moved from treated roots to foliage. It appears root absorption is an important component of flazasulfuron efficacy since most of the absorbed 14C remained in treated leaves and root absorbed 14C moved rapidly to foliage. / Ph. D.

Managing turf for high aesthetic value is costly. Such management usually involves mowing, disease prevention, insect control, and weed control. Mowing is the most expensive practice on golf courses and annual bluegrass (Poa annua L) is the most challenging weed problem in professional turf. The plant growth regulators trinexapac-ethyl and paclobutrazol are commonly used in VA for these two costly and challenging jobs. Prohexadione calcium (PC) is an experimental chemical that inhibits the same enzyme (3ß-hydroxyalase) as trinexapac-ethyl and may selectively suppress annual bluegrass. Experiments were conducted at the Virginia Tech Turfgrass Research Center and Glade Road Research Facility to determine the PC rate required to reduce clipping biomass of four turfgrass species as effectively as trinexapac-ethyl. Prohexadione calcium reduced clipping biomass of bermudagrass (Cynodon dactylon (L.) Pers.), Kentucky bluegrass (Poa pratenis L.), perennial ryegrass (Lolium perenne L.), and zoysiagrass (Zoysia japonica Steud.) equivalent to trinexapac-ethyl at 0.70, 0.22, 0.60, and 0.27 kg a.i./ha -1, respectively. Further experiments conducted at three locations across Virginia determined that PC was comparable to paclobutrazol for annual bluegrass suppression. Since turfgrass response to PC was different between annual bluegrass, Kentucky bluegrass, and perennial ryegrass, 14C labeled PC was used to assess absorption, translocation, and metabolism of PC between annual and Kentucky bluegrass, creeping bentgrass (Agrostis stolonifera L.), and perennial ryegrass. Annual and Kentucky bluegrass absorbed more PC than creeping bentgrass or perennial ryegrass and partially explained the selectivity between these species. Translocation and metabolism of PC did not differ between species. Our final objective launched experiments characterizing possible resistance to acetolactate synthase (ALS) inhibiting herbicides in annual bluegrass. Several selective herbicides for annual bluegrass control inhibit ALS. Since many weeds have developed resistance to ALS-inhibiting herbicides, the ALS gene in annual bluegrass was sequenced and derived amino acid sequences were at least 87% similar to other previously sequenced grass species. This sequencing data will be used in future experiments to predict the likelihood of ALS resistance in annual bluegrass. / Ph. D.

Glyphosate resistant crops were rapidly adopted by farmers since their introduction in 1996 and currently, greater than 90% of cotton and soybean crops are glyphosate resistant. Glyphosate has been an effective mean for controlling Palmer amaranth, however overreliance on glyphosate based systems resulted in weeds that can no longer be controlled with glyphosate. Palmer amaranth resistance to glyphosate has been confirmed in ten US states including Virginia's bordering neighbor North Carolina. The objectives of this study were to i) determine the spread of Palmer amaranth and evaluate awareness among farmers and agribusinesses of herbicide resistant weeds in Virginia; ii) determine the efficacy of commonly used cotton and soybean herbicides programs for Palmer amaranth control; and iii) conduct greenhouse experiments to quantify the level of glyphosate resistance in a Greensville County, Virginia population. Using a communication network of Virginia county extension agents and crop advisers, Palmer amaranth was found in 15 Virginia counties. A survey was conducted to evaluate awareness of herbicide resistance and management of weeds in Virginia. Ninety percent of producers had fields planted to Roundup Ready® crops for each of the last 3 years. One hundred percent of the responders claimed awareness of the potential for weeds to develop resistance to glyphosate, but when asked about how serious they consider weed resistance to herbicides, the responders average rating was of 7.9 (on a scale of 1 to 10 where 1 is "not at all serious" and 10 is "very serious" ). Eighteen percent of the responder population claimed no awareness of glyphosate resistant weeds documented in Virginia. Herbicide efficacy experiments were established in soybean and cotton fields infested with Palmer amaranth. In soybean, experiments were established in a field where Palmer amaranth was not adequately controlled with glyphosate in the previous year. Glyphosate applied at 0.87 + 0.87 + 1.74 kg ae ha⁻¹ at 1, 3, and 5 weeks after planting (WAP) provided 82 to 85% control in 2009, but only 23 to 30% control in 2010, a hot and dry year. Glyphosate applied after preemergence (PRE) herbicides improved control to 90 percent. Programs that included s-metolachlor + metribuzin applied preemergence and followed by glyphosate + fomesafen applied postemergence provided the best control (93%) at 8 WAP. Glufosinate based herbicide programs provided greater than 85% control when applied alone, and control increased to 95% when preceded by PRE herbicides. Many conventional control systems integrating different modes of action provided more than 80% control at final evaluation of Palmer amaranth in 2009 and 2010. In soybean, the most consistent and effective program was flumioxazin applied PRE followed by chlorimuron + thifensulfuron, which provided 99 and 82% control at final evaluation in 2009 and 2010, respectively. Cotton fields were heavily infested with Palmer amaranth, but control with glyphosate had historically been good. Glyphosate applied early postemergence, late postemergence, and late post-directed provided more than 95 percent control at final evaluation of Palmer amaranth. Preemergence applications of fomesafen, fluometuron, or pendimethalin + fomesafen provided 77 to 99 percent early-season control and control was complete with an additional postemergence glyphosate application. Glufosinate applied at 0.45 kg ha⁻¹ at 1 and 3 WAP or applied at 0.45 kg ha⁻¹ following a preemergence herbicide provided greater than 95% control. Greenhouse experiments confirmed Palmer amaranth resistance in a population collected from Greensville County, Virginia. In the first experiment, the resistant biotype's I₅₀ value (rate necessary for 50% inhibition) for dry weight was 1.47 kg ae ha⁻¹, which is 4.6 times greater than the susceptible biotype and 1.7 times the recommended use rate of glyphosate. For fresh weight, the I₅₀ value of the resistant biotype was 1.60 kg ae ha⁻¹, 4.7 times that of the susceptible biotype of 0.34 kg ae ha⁻¹. In the second experiment, the I₅₀ value for the susceptible population could not be determined because all glyphosate rates resulted in complete control. However, the resistant population required 1.01 and 1.30 kg ae ha⁻¹ of glyphosate to reduce the fresh and dry weight by 50%. / Master of Science

Response of Direct-seeded Broccoli to Preemergence Oxyfluorfen and BAS 514 Preemergence treatments of oxyfluorfen at 0.14, 0.28, and 0.56 kg ai/ha caused a 40 to 99% reduction in stand of direct-seeded broccoli, while BAS 514 applied at the same rates caused no reduction in stand. All rates of oxyfluorfen completely controlled Venice mallow while only the 0.56 kg/ha rate of BAS 514 provided acceptable (>70%) control. Broccoli plants that survived preemergence applications of oxyfluorfen exhibited injury ranging from 32 to 97% 6 to 9 weeks after treatment. BAS 514 applied at 0.14, 0.28, 0.56 kg ai/ha provided excellent control of common ragweed with little or no visible crop injury. Common ragweed control with oxyfluorfen varied with soil moisture and organic matter. Applications of 0.28 and 0.56 kg/ha oxyfluorfen significantly reduced yield when compared to the cultivated check. Yields from plots treated with 0.14 kg/ha BAS 514 equalled or exceeded the cultivated check. Treatments of oxyfluorfen and BAS 514 to seeded broccoli caused approximately a one week delay in harvest. Nomenclature: oxyfluorfen, [2-chloro-1-(3-ethoxy-4- nitrophenoxy)-4-(trifluoromethyl)benzene]; BAS 514, quinclorac, (3,7-dicloro-8-quinoline-carboxylic acid); broccoli, [Brassica oleracea(L.) var botrytis]; common ragweed, (Ambrosia artemisifoliaL. #³ AMBEL); Venice mallow (Hibiscus trionum L. #3 HIBTR); Additional index words: Brassica oleracea (L.) botrytis, quinclorac. Weed Control and Crop Yield with Postemergence Applications of Oxyfluorfen, Pyridate, and BAS 514 to Direct-seeded Broccoli Postemergence applications of oxyfluorfen in field studies caused white chlorotic speckling on broccoli foliage. Plants treated with 0.07 kg/ha oxyfluorfen produced yields similar to the cultivated check. High rates of pyridate (4.03 kg/ha) caused yellow lesions on broccoli foliage. Total broccoli yields from plots treated with pyridate at 0.28 and 0.50 kg/ha were not significantly different from the cultivated check. BAS 514 caused moderate growth stunting to broccoli in field studies. At two out of four locations, injury increased with time. At these sites, total broccoli yield from plots treated with 0.28 and 0.56 kg/ ha BAS 514 was lower than the cultivated check. Total number of broccoli heads per hectare for plots treated with BAS 514 equaled or exceeded that of the cultivated check. Broccoli treated with BAS 514 plus the experimental adjuvant BAS 090 showed increased injury and decreased yield with increasing rates when compared to applications of BAS 514 alone. Broccoli developed foliar veinal chlorosis and whitish elongated heads following applications of BAS 514 plus BAS 090. High rates of BAS 514 (0.56 kg/ha) with or without BAS 090 reduced average head weight. Little to no stand reduction or delay in harvest was observed with any herbicide treatment. A two fold safety margin for herbicide rate was observed for oxyfluorfen at 0.07 kg/ha, pyridate at 0.50 kg/ha and BAS 514 at 0.14 kg/ha. In greenhouse studies, oxyfluorfen at 0.28 kg/ha provided >90% control of common ragweed and common lambsquarters, and 77% control of common pigweed. Pyridate at 2.02 kg/ha provided excellent control of horseweed, and greater than 70% control of prickly sida, common ragweed and common lambsquarters. All rates of pyridate controlled common pigweed. Applications of BAS 514 at 0.14 to 0.56 kg/ha provided 88 to 100% control of horseweed and 76 to 82% control of common ragweed. Greater than 90% control of large crabgrass was observed with BAS 514 plus BAS 090 at 0.28 kg/ha. Nomenclature: oxyfluorfen, 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene; pyridate 6-chloro-3-phenylpyridazine-4-yl-S-octyl carbonothionate; BAS 514, quinclorac, 3,7-dichloro-8-quinoline-carboxylic acid; broccoli Brassica oleracea L. var. botrytis; common ragweed Ambrosia artemisiifolia L. #3 AMBEL; redroot pigweed Amaranthus retroflesus L. #AMARE; common lambsquarters Chenopodium album L. #CHEAL; Prickly sida Sida spinosa L. #SIDSP; Horseweed Conyza canadensis L. #ERICA; Large crabgrass Digitaria sanguinalis L. #DIGSA; Additional index words. quinclorac, BAS 090, Brassica oleracea L. botrytis. / Master of Science

Experiments were conducted on the use of granular fenuron, 25% active, for white pine release and establishment. The effect of fenuron on the plant community was also investigated. Studies included in the white pine release experiment were the effect of season of treatment on the kill of hardwoods and percentage survival of indigenous white pine, and the effectiveness of fenuron on various species of hardwoods. All hardwood stems over six feet tall were treated with four grams of active fenuron placed on the soil at the base of the tree. Treatments were made in May 1960, August 1960, and March 1961. The May treatment was most effective in the removal of the hardwoods. There was a reduction of 59% of pines over six feet tall and an increase of 45% of pines less than six feet tall. Red maple and the oaks were the species most susceptible to the treatment; whereas, chestnut, sassafras, and black locust were the least susceptible. In the white pine establishment experiment, the residual effect of fenuron on white pine seedlings, and its effectiveness at a lower rate on various hardwoods were lnvestigated. Each hardwood stem over six feet tall was treated with one gram active fenuron in the spring of 1960. In March 1961, 100 white pine seedlings were planted in each of three plots previously treated. Five months after planting there was 99% survival of the pine seedlings. The one-gram rate was effective against red maple and the oaks but had little effect on sassafras, cucumber tree, and chestnut. Fenuron in some manner changed the composition of the plant community. Fireweed, poke, and several species of Panicum were present in the treated plots but were not present in the untreated buffer strips. / Master of Science

The potential of CGA-136872 (3-[4,6-bis(difluoromethoxy) pyrimidin-2-yl-1-(2-methoxycarbonyl-phenylsulfonyl) urea) and DPX-V9360 (3-pyridinecarboxaminde, 2-(((4,6-dimethoxy pyrimidin-2yl) aminocarbonyl)) aminosulfonyl) ))-N,N-dimethyl) were investigated for postemergence use in corn, including corn tolerance, weed control and combinations of CGA-136872 with other postemergence corn herbicides for weed control. CGA-136872 Applied at rates of 1.2, 2.5, 5.0 and 10.0 times the suggested recommended use rate in corn (variety Southern States 565) caused more injury at the 5-leaf stage than at the 7- and 9-leaf stage of corn. Recovery from injury was rapid and complete at 5 weeks after treatment (WAT) and no yield reduction was observed. Several corn varieties treated with twice the suggested use rate of CGA-136872 and DPX-V9360 showed injury that was both herbicide and variety dependent. Most injury occurred at 1 and 2 WAT. Corn recovery was complete at 5 WAT, but yield reduction on some varieties was observed with CGA-136872 treatments. In the weed control study, both herbicides showed high activity on johnsongrass (Sorghum halepense (L.) Pers.), giant foxtail (Setaria faberi Herr.), common lambsquarters (Chenopodium album L.) and redroot pigweed (Amaranthus retroflexus L.), particularly with early applications. However, johnsongrass rhizome regrowth prevented full season control of this species with early postemergence applications. Combinations of CGA-136872 with several other herbicides resulted in significant benefit in control of common lambsquarters and redroot pigweed while johnsongrass and giant foxtail control was not improved. Reduced control of johnsongrass was observed when CGA-136872 was applied in combination with paraquat (1,1’-dimethy1-4,4’-bipyridilium ion). Similar results were observed for giant foxtail control when CGA-136872 was applied with 2,4-D ((2,4-dichlorophenoxy) acetic acid) and dicamba (3,6-dichloro-2-methoxybenzoic acid). Results of this research indicate that both CGA-136872 and DPX-V9360 have good potential for postemergence use in corn, and could represent an important supplement to existing postemergence corn herbicides. / Master of Science

There is a growing interest in agricultural spray drone (ASD) use for herbicide application in managed turfgrass systems, which historically has precluded aerial application. Considering pesticide deposition accuracy is of utmost importance in managed turfgrass systems, a thorough examination of factors that influence ASD spray deposition patterns is needed. A python-based spray deposition pattern analysis tool, SprayDAT, was developed to estimate spray quality utilizing a cost-effective continuous sampling technique involving digital soand spectrophotometric analysis of blue colorant stains on white Kraft paper. This technique cost 0.2 cents per USD spent on traditional water-sensitive paper (WSP) allowing for continuous sampling necessary for the highly variable deposition patterns delivered by an ASD. SprayDAT conserved droplet densities and more accurately detected stain objects compared to a commonly utilized software, DepositScan, which overestimated stain sizes. However, droplet density exhibited an upper asymptote at 22% stain cover when relating volume median diameter (VMD) due to increasing overlap of stain objects. Spread factor of blue colorant stains was fit to a 2-parameter power equation when compared across six discrete droplet sizes between 112 and 315 µm when droplets were captured in a biphasic solution of polydimethylsiloxane of 100 cSt over 12,500 cSt viscosities. Cumulative digitally assessed stain objects underestimated application volume 270% when compared to the predicted output based on flow rate, coverage, and speed. SprayDAT incorporates a standard curve based on colorant extraction and spectrophotometric analysis to correct this error such that total stain area accurately estimates application volume to within 9%. This relationship between extracted colorant and total stain area, however, is dependent on droplet size spectra. SprayDAT allows users to customize standard curves to address this issue. Using these analysis techniques, continuous sampling of a 29.3-m transect perpendicular to an ASD or ground sprayer spray swath resolved that increasing ASD operational height increases drift and effective swath width while effective application rate, total deposition, and smooth crabgrass control by quinclorac herbicide decreases. Deposition under the ASD was heterogeneous as the coefficient of variation (CV) within the targeted swath exceeded 30% regardless of operational height. At higher operational heights, relative uniformity of spray pattern was improved but droplet density at 11.7 m away from the intended swath edge was up to four times greater and total spray deposited was up to 60% reduced at the highest heights. For each 1-m increase in ASD operational height, 6% of the deposited spray solution, 11% of the effective application rate within the targeted swath, and 7% of smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] population reduction declined. Subsequent studies suggested that total deposition loss with increasing operational height of ASD were likely due to droplet evaporation. Discrete-sized droplets subjected to a 5-m fall in a windless environment exhibited a sigmoidal relationship where 98% volume of 135-µm droplets and approximately 67% volume of 177 – 283 µm diameter droplets evaporated. Addition of drift reduction agents (DRAs) or choosing different nozzle types altered the initial droplet density generated by a flat-fan nozzle. Regardless of DRA additions or nozzle replacement, the distance required to lose 50% of small droplets (< 150 µm diameter) was 6.6 m. Air induction nozzles and DRA admixtures also conserved smooth crabgrass control across 2- and 6-m operational heights, where control was reduced at the 6-m height with a flat fan nozzle without DRA. Spray deposition pattern analysis for multipass ASD and ground applications was conducted by utilizing nighttime UV-fluorescence aerial photography and weed infestation counts in a digitally overlaid grid. Results show that under-application across all devices was consistent and averaged 12%, whereas at least 14% more over-application on the targeted area was observed for ASD, regardless of equipped nozzle types, compared to a ride-on sprayer. Drift also occurred at least 3 times more for ASD application than for a ride-on sprayer and a spray gun sprayer. Using smooth crabgrass infestation annotated from aerial images could not consistently resolve the spatial variability evident in UV-fluorescent imagery presumably due to the innate variability in weed populations. Analysis using SprayDAT revealed insights into factors affecting ASD spray deposition, such as operational height impacting drift, effective swath width, and herbicide efficacy, highlighting the tool's utility in optimizing aerial herbicide applications in turfgrass management. Data suggest that the lowest ASD operational height should be employed to partially mitigate drift and droplet evaporation while improving weed control. Lower operational heights, however, reduce effective swath width and increase heterogeneity of the deposition pattern. Future research should evaluate possible engineering controls for these problems. / Doctor of Philosophy / In recent years, there has been growing interest in using agricultural spray drones (ASD) for applying herbicides in managed turfgrass systems. Traditionally, aerial spraying has not been widely used in these settings, but ASDs are gaining attention. However, there is still a need for a better understanding of how different factors affect spray patterns of ASDs and weed control effectiveness. To address this, novel image analysis software, SprayDAT was developed. It uses white Kraft paper and blue colorant to analyze spray patterns. Compared to traditional methods, SprayDAT provides a cost-effective way to study spray deposition over larger areas, which is important for analyzing the irregular patterns produced by ASDs. The tool showed similar accuracy in detecting spray patterns compared to existing software used with water-sensitive papers, but with some improvements in detecting fine details. SprayDAT was used to analyze spray patterns from ASDs equipped with different nozzles at various heights, as well as ground application methods. It was found that regardless of height, ASDs showed some inconsistency in spray deposition, with about 6% of the spray solution and 11% of the effective application rate being lost for each 1-m increase in ASD height. This loss is likely due to droplet evaporation based on additional laboratory and field studies that directly measured droplet volume loss or stains of small droplets on white paper. In another part of the study, UV-fluorescent nighttime aerial images and weed infestation following herbicide sprays were used to assess spray deposition of multipass ASD applications. It was found that ASDs tended to over-apply in more of the targeted area than ground-based methods and caused more drift of spray to non-target areas. These studies suggest that lower operational heights, such as 2-m above ground, is recommended when controlling weeds with an ASD as effective application rate and weed control will be improved. These low heights, however, increase variability of rate across the intended spray swath and reduce the effective swath width.

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 1985 G672 / Master of Science

No description available.