Field and laboratory studies were conducted to determine the ecological and physiological responses of phytoplankton to environmentally significant concentrations of atrazine, diuron, and 2,4-D. Field results would indicate that all three herbicides have a significant effect on species diversity and species dominance. Atrazine and diuron were particularly effective in decreasing diversity in concentrations of 10 ppb to 1.0 ppm. While total biomass as measured by ATP decreased significantly for both atrazine and diuron, total chlorophyll levels increased significantly in 0.1 mg/l atrazine. Decreases in chlorophyll were noted for all other concentrations tested in atrazine and diuron. Blue-green algae Gloeocapsa sp. and Synecchoccus sp. were the predominant genera in the 0.1 mg/1 atrazine. 2,4-D tests also resulted in significant increases in chlorophyll over control replicates. Additionally, biomass as measured by ATP indicated significant increases over control values in 10 mg/1 2,4-D suggesting that 2,4-D may have stimulated the growth of algae or that select algae within the test were able to take a competitive advantage in the presence of 2,4-D. This result was not consistent however. Laboratory tests using continuous cultures of Chlorella sorokiniana indicated that both atrazine and diuron were effective toxicants in low concentrations. Diuron was an effective growth inhibitor in a range of concentration from 0.0014 to 0.01 mg/l. Atrazine was an effective growth inhibitor from 0.014 to 0.1 mg/l. 2,4-D stimulated the growth of continuously cultured Chlorella sorokiniana in a range of concentration from 8.6 to 20 mg/l as measured by cell counts, total organic carbon, in vivo chlorophyll fluorescence, and ATP. The data indicated that the effect was not due to the utilization of 2,4-D as a carbon source but to an actual enhancement of the photosynthetic process. The uptake of radioactively labeled carbon (¹⁴c added as H¹⁴CO₃) was significantly increased in the presence of 2,4-D. The literature contains several reports of enzyme activity stimulation by 2,4-D (108). The data supported the suggestion that 2,4-D may influence the Hill reaction and respiration by stimulating an enzyme (or enzymes) involved in these processes. The net result may have been an increase in the rates of reactions in both the Calvin cycle and photorespiration. / Ph. D.

In situ microcosms of a planktonic community were exposed to the triazine herbicide simazine. Randomly selected sets of microcosms were collected and sampled each week for three weeks (plus Week 0). Samples of ambient water were collected each week for evaluation of enclosure effects. Physical and chemical parameters were measured per microcosm. Simazine was measured at Weeks 0 and 3 only. The following organisms were preserved and quantified: phytoplankton, bacteria, and zooplankton, including ciliates, copepod nauplii, cladocerans and rotifers. Simazine decreased dissolved oxygen and pH, but increased nitrate and ammonia concentrations compared to control microcosms. A temporary decrease in temperature occurred at Week 1. Phytoplankton were differentially affected by simazine. Sensitive taxa included Trachelomonas, Glenodinium, diatoms and several species of relatively minor significance. Dinobryon and miscellaneous coccoids were not significantly affected. Phytoplankton ≥9 um were more affected by simazine than phytoplankton <9 um. Many cells <9 um may be facultative or obligate heterotrophs and not susceptible to simazine. Although data were variable, bacteria were also not affected by phytoplankton changes or simazine. Rotifers were the major zooplankters and the two dominant species, Kellicottia bostoniensis and Keratella cochlearis, were reported to graze exclusively on cells <9 um. Polyarthra vulgaris and Synchaeta pectinata also graze in this size range but are not limited to it. Copepod nauplii/copepodids were present, but adult copepods and cladocerans were rare. The tintinnid ciliate Codonella exhibited a temporary population increase during the study. Zooplankton were not affected by simazine-induced changes in the phytoplankton. Kellicottia bostoniensis was the only zooplankter affected by simazine: it had lesser mortality in higher concentrations of simazine. Possible reasons for this enhanced survival were discussed. The zooplankton (primarily rotifers) appeared to feed more on heterotrophic cells than on autotrophic cells, largely as a function of food size, and may have been more closely associated with the detrital food chain than the autotrophic food chain. / M.S.

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

no abstract provided by author / Master of Science

Palmer amaranth (Amaranthus palmeri) and common ragweed (Ambrosia artemisiifolia) are two of the most troublesome weeds in soybean. Both weeds possess widespread resistance to glyphosate and acetolactate synthase (ALS) inhibiting herbicides resulting in the use of protoporphyrinogen oxidase- (PPO) inhibitors to control these biotypes, although PPO-resistant biotypes are increasing. New soybean herbicide-resistant trait technologies enable novel herbicide combinations. Combinations of two herbicide sites-of-action (SOA) improved control 19 to 25% and 14 to 19% of Palmer amaranth and common ragweed, respectively, versus using one SOA (mesotrione, dicamba, 2,4-D, or glufosinate alone). Seed production of 5 to 10 cm Palmer amaranth and common ragweed was reduced greater than 76% by fomesafen, auxin (dicamba and 2,4-D), or glufosinate containing treatments. Some weeds survived and set seed even when treated at the proper size. As weed size increased from 10 to 30 cm, control diminished and fecundity increased, underscoring the importance of proper herbicide application timing. Effective preemergence herbicides reduced the number of weeds present at the postemergence application compared to no treatment, reducing the likelihood of herbicide resistance development. Dicamba, 2,4-D, or glufosinate applied alone or auxin + glufosinate combinations reduced Palmer amaranth seed production greater than 95% when applied at first visible female inflorescence; this first report, in addition to previous reports on individual herbicides, indicates this application timing may be useful for soil seed bank management. This research informs mitigation of herbicide resistance spread and development. / Master of Science in Life Sciences / Over 30 million hectares of soybeans were harvested in 2019 in the United States, totaling over $31 billion in value. Two of the most troublesome weeds in soybean, Palmer amaranth (Amaranthus palmeri) and common ragweed (Ambrosia artemisiifolia) can cause even greater yield reductions in soybean, up to 79 to 95%, respectively. Frequent, exclusive, and repeated use of a single herbicide has led to multiple herbicide-resistance in both of these weeds. Co-applying two effective herbicides reduces the likelihood of resistance development. New soybean varieties have been genetically modified for resistance to herbicides that were previously unusable, allowing new herbicide combinations. Research was established to investigate these herbicide options to control and reduce seed production of Palmer amaranth and common ragweed with the overarching goal of mitigating herbicide resistance, particularly resistance to protoporphyrinogen oxidase (PPO) inhibiting herbicides, which are a critical part of herbicide options in soybean production. Preemergence herbicides are vital tools in herbicide programs, reducing the number of weeds present at a postemergence application and thereby reducing the risk of herbicide resistance development to the postemergence herbicide. PPO herbicides (flumioxazin, sulfentrazone, or fomesafen) applied preemergence reduced Palmer amaranth and common ragweed density at the postemergence application 82 to 89% and 53 to 94%, respectively. The preemergence herbicide used did not affect control four weeks after the postemergence herbicides were applied. Postemergence herbicides were applied targeting three weed heights: 5 to 10 cm (ideal), 10 to 20 cm, and 20 to 30 cm. Control decreased as weed height increased and larger weeds had greater biomass and seed production, underscoring the importance of proper herbicide application timing. The single site-of-action treatments dicamba, 2,4-D, glufosinate, or fomesafen resulted in greater than 85 and 92% morality of 5 to 10 cm Palmer amaranth and common ragweed, respectively. Palmer amaranth and common ragweed control improved by 19 to 25% and 14 to 19%, respectively, when using two herbicide sites-of-action increased versus using one SOA (mesotrione, dicamba, 2,4-D, or glufosinate alone). The use of two herbicide sites of action resulted in maximum biomass reductions, depending on weed height, of 57 to 96% and 73 to 85% for Palmer amaranth and common ragweed, respectively. Dicamba, 2,4-D, glufosinate alone and in combination with fomesafen reduced seed production (relative to the nontreated) of 5 to 10 cm Palmer amaranth and common ragweed greater than 98 and 76%, respectively. Dicamba, 2,4-D, and glufosinate applied alone or auxin (dicamba and 2,4-D) and glufosinate combinations reduced Palmer amaranth seed production greater than 95% when applied at first visible female inflorescence. This indicates that these herbicides may be useful in soil weed seed bank management. This research reinforces the utility of PPO herbicides for preemergence control and their efficacy postemergence when combined with another effective herbicide, a practice known to reduce herbicide resistance development. This research also reinforces the potential for dicamba, 2,4-D, or glufosinate to reduce weed seed production when applied at a delayed timing. Future research should investigate the progeny of these weeds treated with herbicides at a delayed timing to evaluate the potential for this practice to reduce herbicide resistance development.

Field experiments were conducted in 1984 and 1985 in Fluvanna and Montgomery Counties in Virginia, to evaluate HOE-O661 (glufosinate) [ammonium-(3-amino-3-carboxypropyl )-methyl phosphinate], cyanazine (2-[[4-chloro-6-(ethylamino )-s-triazin-2-yl]amino]-2-methyl propionitrile)), glyphosate [N-(phosphonomethyl)glycine] and paraquat (1,1'-dimethyl 4,4'-bipyridinium ion) for the control of vegetation existing at the time of no-till corn establishment. These herbicides were applied alone or in combination with 2,4-D [(2,4-dichlorophenoxy)acetic acid] or dicamba (3,6-dichloro-2-methoxybenzoic acid) at three timings of application. Both locations were heavily infested with annual, biennial, and perennial broadleaf weeds, including horseweed (Conyza canadensis), buckhorn plantain (Plantago lanceolata), field bindweed (Convolvulus arvensis), curly dock (Rumex crispus) and wild mustard (Sinapis arvensis). All four non-selective herbicides provided good overall weed control. The addition of 2,4-D or dicamba generally improved the control of broadleaf weeds in all four experiments. Control of horseweed with paraquat was variable, but improved significantly when dicamba was applied in combination with paraquat. Glyphosate, cyanazine and HOE-O661 alone or in combination with 2,4-D or dicamba provided excellent horseweed control. Wild mustard control with glyphosate was dependent on the weed size and growth stage of development. Control with paraquat, cyanazine and HOE-0661 was not affected by differences in wild mustard size or growth stage. Glyphosate and HOE-0661 provided acceptable field bindweed control alone, and all herbicides gave excellent field bindweed control when applied in combination with 2,4-D or dicamba. Cyanazine and HOE-0661 showed better control of shoot growth on the more difficult-to-control weeds than paraquat and glyphosate when applied alone. With the addition of either 2,4-D or dicamba, cyanazine and HOE-0661 provided better overall weed control, in most cases, than corresponding paraquat and glyphosate combinations. Timing of application and weed size did not significantly affect herbicide activity, even at later application timings when weeds were well established and exceeded 60 cm in height. / M.S.

Avec ses grains nus et sa valeur nutritive exceptionnelle, l'avoine nue (Avena sativa L. var nuda) est une céréale très intéressante pour plusieurs marchés niches. Toutefois, l'avoine nue récoltée au Québec développe en moyenne 10 % de grains vêtus et parfois davantage. L'objectif de ce projet était de détenniner l'effet de l'environnement et des herbicides sur la proportion de grains vêtus, la teneur en huile, les profils d'acides gras et la teneur en protéines des génotypes d'avoine nue. Les résultats démontrent que la proportion de grains vêtus est influencée par l'environnement, le type de sol, les herbicides et leur stade d'application. Les proportions de grains vêtus les plus élevées ont été obtenues à deux sites différents en 2006 et 2007. Plus de grains vêtus ont été produits sur le loam sableux que sur le loam. L'application de l'herbicide dicamba/MCPA au stade 12-13 de Zadoks a augmenté la proportion de grains vêtus et son application au stade 22-23 l'a accrue davantage. Quel que soit leur stade d'application, les herbicides bromoxynil/MCPA et thifensulfuron méthyle/tribenuron méthyle n'ont pas produit plus de grains vêtus que le témoin désherbé manuellement. Toutefois, des différences appréciables dans la réaction des génotypes ont été notées. Les génotypes qui produisent beaucoup de grains vêtus ont montré de grandes variations entre les sites et les herbicides. La teneur en huile et les profils d'acides gras de l'avoine nue sont influencés par l'environnement. C'est au site le plus frais que les teneurs en huile ont été les plus élevées et ce n'est pas le même site qui a donné la teneur la plus élevée pour tous les acides gras. Les herbicides ont eu un effet significatif sur les génotypes à teneur élevée en huile seulement une année sur deux. L'herbicide dicamba/MCPA a diminué la teneur en huile et en acide linoléique et l'herbicide bromoxynil/MCPA a réduit la teneur en acide oléique. Les résultats de ce projet montrent que l'utilisation des herbicides, tel que le dicamba/MCPA, sont à éviter pour le désherbage de l'avoine nue.

The activity and the selectivity of cycloxydim {2-[1-(ethoxyimino)butylJ-3-hydroxy- 5-(2H-tetrahydrothiopyran-3-yl)-2-cyclohexen-l-one}, code designation BAS 517, were examined flIst with etiolated seedlings of com (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Etiolated soybean seedlings were not affected by cycloxydim. The degree of growth inhibition of com varied with concentration of cycloxydim and incubation time. Compared to mesocotyls and coleoptiles, radicles of corn were the most sensitive to cycloxydim. Meristematic tissues appeared to be the site of action of cycloxydim as root meristems were the first to show symptoms. A band of reddening tissue developed at meristematic tips followed by the complete cessation of root growth. In a study comparing activities of technical grade and formulated cycloxydim and sethoxydim, {2-[ l-(ethoxyimino )butyl}- 5-[2-(ethylthio )propy11-3-hydroxy-2-cyclohexen-l-one}, formulated compounds were more potent than the technical grade chemicals without formulation additives. Technical sethoxydim was more potent than technical cycloxydim. Root tips excised from com and soybean seedlings were used subsequently for cycloxydim treatments. The activity and selectivity of cycloxydim expressed at the isolated root tip level were similar to those of cycloxydim bioassayed with whole seedlings. However, root tips appeared to be more sensitive than the whole seedlings. Injury at the tissue and cell levels of the 2-mm root tips that were treated with various concentrations of cycloxydim was examined after 24 hours incubation. Concentrations of 0.1, 1, and 10 μM cycloxydim caused severe cell vacuolization. A gradient of decreasing injury from epidermal cells toward the center of roots was observed. This pattern of injury appeared to reflect the penetration of cycloxydim into roots along a concentration gradient. / Ph. D.

The compatibility of ACP 2100, a member of the imidazolinone family (chemistry not released), imazaquin (2- [4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H̱-imidazol2- yl]-3-quinolinecarboxylic acid) and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid} was investigated for use in a turf management program, including growth regulation and broadleaf weed control. Field and greenhouse results indicated an antagonistic interaction between triclopyr and imazaquin for control of common dandelion (<i>Taraxacum officinale</i> Weber in Wigger). Addition of imazaquin at 276 g ha⁻¹ to triclopyr at 138 g ha⁻¹ resulted in less dandelion control than 138 plus 138 g ha⁻¹, respectively. Greenhouse and laboratory studies indicated a synergistic interaction between ACP 2100 and triclopyr, not apparent in the field. Addition of ACP 2100 to triclopyr at 34 and 69 g ha⁻¹ resulted in less than expected dandelion biomass, indicating increased dandelion control. ACP 2100 initially decreased triclopyr uptake, but resulted in greater uptake 48 hours after treatment. ACP 2100 also increased triclopyr translocation to the crown, root and middle rosette leaves. In the field and greenhouse, triclopyr did not influence growth regulation and decreased turf injury caused by ACP 2100. Studies showed that as the rate of ACP 2100 increased with the rate of triclopyr an antagonism occurred, resulting in decreased turf injury. The low rate of both ACP 2100 and imazaquin in combination resulted in equal turf growth regulation activity to the high rate of either chemical alone or in combination. One greenhouse study indicated that the interaction was synergistic for height suppression with ACP 2100 and imazaquin at rates of 12 plus 17 or 24 g ha⁻¹, respectively. However, field studies showed that ACP 2100/imazaquin combinations resulted in unacceptable injury to ‘l90’ and ‘Glade-Plush-Ram’ Kentucky bluegrass (<i>Poa pratensis</i> L.). The best turf quality, growth regulation and dandelion control was achieved with a combination of ACP 2100 at 96 and 144 g ha⁻¹ plus triclopyr at 276 g ha⁻¹. These results indicate that turf management costs may be reduced without sacrificing dandelion control by incorporating a chemical mowing program into a spring herbicide treatment. / Ph. D.

In full-season-soybean weed management experiments, the addition of glyphosate [N-(phosphonomethyl)glycine], paraquat (1,1'-dimethyl-4,4'-bipyridinium ion), or HOE-0661 [ammonium (3-amino-3-carboxypropyl)methylphosphinate] to chlorimuron [2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino] carbonyl]amino]sulfonyl] benzoic acid] plus linuron [N'- (3,4-dichlorophenyl)-N-methoxy-N-methyl urea] was required for effective weed control, especially of eastern black nightshade (Solanum ptycanthum Dun.). In double-crop experiments over 4 years including 10 experimental sites and 8 different weeds, chlorimuron plus linuron provided good control of vegetation at planting and residual weed control without glyphosate, paraquat, or HOE-0661. Cyanazine [2-[[4-chloro-6-(ethylamino)-1,3,5-triazin- 2-yl]amino]-2-methylpropanenitrile] and 2,4-D [(2,4- dichlorophenoxy)acetic acid] were the most effective herbicides for horseweed (Conyza canadensis (L.)Cronq.) control prior to establishing full-season no-till soybeans (Glycine max (L.)Merr.). In greenhouse experiments, emergence of tobacco (Nicotiana tabacum L.) seedlings was severely inhibited by all chlorimuron-containing treatments and by the highest rates of imazaquin [2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid]. Growth of tobacco transplanted into a treated potting mixture was severely reduced by all rates of chlorimuron-containing herbicides, and to a lesser extent by imazaquin. Postemergence applications of chlorimuron alone or imazaquin did not significantly affect tobacco growth. In the greenhouse, 'Vance' and 'Forrest' soybean varieties were more sensitive to chlorimuron than were 'W-20' (a sulfonylurea-resistant variety), 'Essex', or 'Hutcheson'. Herbicide injury increased with increasing soil pH. Under simulated rainfall conditions, chlorimuron movement in soil increased with increasing pH and rainfall. Soybean injury may be more directly related to chlorimuron in the soil water solution than to the amount of chlorimuron present in the soil profile. Laboratory experiments indicated that tolerance of pitted (Ipomoea lacunosa L.) and entire leaf (Ipomoea hederacea var. integriuscula Gray) morningglories to chlorimuron may be due to reduced herbicide uptake. Sensitivity of 'Vance' soybeans may be associated with the inability to rapidly metabolize chlorimuron herbicide. / Ph. D.