Charles T. Bryson

Purple Nutsedge (Cyperus rotundus) Population Dynamics in Narrow Row Transgenic Cotton (Gossypium hirsutum) and Soybean (Glycine max) Rotation

A 4-yr field study was conducted during 1998 through 2001 at Stoneville, MS, to determine the effects of narrow-row transgenic cotton and soybean rotation on purple nutsedge populations and crop yield. Crop rotations over 4 yr included cotton and soybean sown in the following patterns: CCSS, CSCS, SCSC, SSCC, and continuous cotton (CCCC) and soybean (SSSS), where cotton is denoted as (C) and soybean as (S), all with herbicide programs that were glyphosate based, non–glyphosate based, or no purple-nutsedge control (NPNC). Purple nutsedge populations and shoot dry biomass were reduced in cotton and soybean rotation and continuous soybean by 72 and 92%, respectively, whereas in continuous cotton, purple nutsedge populations increased by 67% and shoot dry biomass was reduced by 32% after 4 yr. Reductions in purple nutsedge populations also occurred in soybean when cotton was rotated with soybean (CSCS and SCSC), compared with continuous cotton. Among herbicide programs, the glyphosate-based program was more effective in reducing purple nutsedge populations, compared with the non–glyphosate-based program. Seed cotton yield was greater with cotton following soybean (SCSC) than with cotton following cotton (CCCC, CCSS) in 1999. However, seed cotton yields were similar regardless of crop rotation systems in 2000 and 2001. Seed cotton yields were equivalent in the glyphosate-based and non–glyphosate-based programs in 1999 and 2001. During 1999 to 2001, seed cotton yields were reduced by 62 to 85% in NPNC compared with yields in glyphosate- and non–glyphosate-based programs. Soybean yields were unaffected by crop rotation systems in all the 4 yr. Among herbicide programs, non–glyphosate-based program in all 4 yr and glyphosate-based program in 1999 and 2000 gave higher soybean yield compared with NPNC. After 4 yr of rotation, purple nutsedge tubers and plant density were highest in continuous cotton and lowest in continuous soybean. Both herbicide programs reduced tubers per core and plant density compared with NPNC, and the glyphosate-based program was more effective than the non–glyphosate-based program. These results show that in cotton production, severe infestations of purple nutsedge can be managed by rotating cotton with soybean or by using glyphosate-based herbicide program in glyphosate-resistant cotton. Nomenclature: Glyphosate; purple nutsedge, Cyperus rotundus L. #3 CYPRO; cotton, Gossypium hirsutum L. ‘DP 436RR’; soybean, Glycine max (L.) Merr. ‘DP 5806RR’. Additional index words: Purple nutsedge tuber, transgenic crop. Abbreviations: fb, followed by; NPNC, herbicide program with no purple-nutsedge control; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Effect of Cogongrass (Imperata cylindrica) Extracts on Germination and Seedling Growth of Selected Grass and Broadleaf Species1

The effects of cogongrass foliage and root residue extracts on germination and radicle and coleoptile growth of barnyardgrass, browntop millet, bermudagrass, hemp sesbania, Italian ryegrass, and prickly sida were investigated in laboratory experiments. Liquid extracts of cogongrass foliage and root residues at concentrations of 0, 0.25, 0.5, 1, 2, 4, and 8% were evaluated on bermudagrass and Italian ryegrass. Effects of 8% foliage or root residue extracts were investigated on hemp sesbania, prickly sida, barnyardgrass, and browntop millet. Cogongrass residue (foliage and root) extracts at concentrations as low as 0.5% inhibited germination and seedling growth of bermudagrass and Italian ryegrass. Germination of bermudagrass and Italian ryegrass was reduced by as much as 62% and radicle and coleoptile growth by as much as 96% at the highest extract concentrations. Foliage and root residue extracts reduced germination of barnyardgrass, browntop millet, and prickly sida 52 to 64% and seedling growth by as much as 96%. Cogongrass extracts had no effect on germination or seedling development of hemp sesbania. Results indicate that extracts of cogongrass may contain allelochemicals that may contribute to its invasiveness and extreme competitiveness. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; bermudagrass, Cynodon dactylon (L.) Pers. # CYNDA; browntop millet, Brachiaria ramosa (L.) Stapf. # PANRA; cogongrass, Imperata cylindrica (L.) Beauv. # IMPCY; hemp sesbania, Sesbania exaltata (Raf.) Rydb. Ex A. W. Hill # SEBEX; Italian ryegrass, Lolium multiflorum Lam. # LOLMU; prickly sida, Sida spinosa L. # SIDSP. Additional index words: Allelopathy, coleoptile, germination, plant extracts, plant residues, radicle.

Ragweed Parthenium (Parthenium hysterophorus) Control with Preemergence and Postemergence Herbicides

Field and greenhouse experiments were conducted during 2005 and 2006 at Stoneville, MS, to determine control of ragweed parthenium with several preemergence (PRE) and postemergence (POST) herbicides registered for use in corn, cotton, peanut, rice, and soybean. Norflurazon, pendimethalin, clomazone, diuron, fluometuron, pyrithiobac, dimethenamid, flumetsulam, imazaquin, s-metolachlor, metribuzin, chlorimuron, atrazine, simazine, flumioxazin, and quinclorac were applied PRE. Ragweed parthenium control was highest with norflurazon (100%) and clomazone (100%) followed by fluometuron (96%), metribuzin (90%), diuron (87%), flumioxazin (84%), chlorimuron (77%), and quinclorac (67%) at 6 wk after treatment (WAT) under greenhouse conditions. Control of ragweed parthenium was less than 58% with all other herbicides. Ragweed parthenium appears to be highly sensitive to pigment and photosynthetic inhibitors compared to herbicides with other modes of action. Glyphosate, glufosinate, paraquat, bentazon, acifluorfen, chlorimuron, halosulfuron, MSMA, bromoxynil, atrazine, 2,4-D, flumioxazin, trifloxysulfuron, and clomazone were applied POST to field-grown rosette and bolted plants. Glyphosate, glufosinate, chlorimuron, and trifloxysulfuron applied at rosette stage provided greater than 93% control of ragweed parthenium at 3 WAT. Halosulfuron, MSMA, bromoxynil, 2,4-D, and flumioxazin controlled 58 to 90% rosette ragweed parthenium at 3 WAT. Ragweed parthenium control with all other POST herbicides was less than 38%. At bolted stage, glyphosate, glufosinate, and trifloxysulfuron controlled 86 to 95% ragweed parthenium and control was 61 to 70% with chlorimuron, halosulfuron, and 2,4-D 3 WAT. Overall, efficacy of POST herbicides was better on rosette plants than on bolted plants. Amino acid synthesis and glutamine synthase inhibitors were more active than herbicides with other modes of action. These results indicate that norflurazon, clomazone, fluometuron, flumioxazin, halosulfuron, chlorimuron, and trifloxysulfuron could provide effective control of ragweed parthenium. Nomenclature: Acifluorfen; atrazine; bentazon; bromoxynil; chlorimuron; clomazone; 2,4-D; dimethenamid; diuron; flumetsulam; flumioxazin; fluometuron; glufosinate; glyphosate; halosulfuron; imazaquin; s-metolachlor; metribuzin; MSMA; paraquat; quinclorac; simazine; trifloxysulfuron; ragweed parthenium, Parthenium hysterophorus L. PTNHY; corn, Zea mays L; cotton, Gossypium hirsutum L; peanut, Arachis hypogaea L; rice, Oryza sativa L; soybean, Glycine max (L.) Merr.

Ecotype Variability and Edaphic Characteristics for Cogongrass (Imperata cylindrica) Populations in Mississippi

Abstract Cogongrass is a highly invasive, perennial grass that is found on all continents, except Antarctica. It continues to spread at an alarming rate in the southeastern United States. Cogongrass has been reported from a wide array of habitats; however, soils from areas where cogongrass grows have never been characterized. Live cogongrass plants, herbarium specimens, and soil samples were collected from 53 cogongrass populations from across the 10 physiographic regions and land use areas in Mississippi. Cogongrass leaf and inflorescence morphology varied among sites, and plants were found in soils varying widely in texture (ranging from 28 to 86% sand, 3 to 48% silt, and 6 to 43% clay), organic matter content (ranging from 0.9 to 5.0%), pH (ranging from 4.4 to 8.0), and nutrient status: 6 to 190 kg ha−1 (15 to 470 lb A−1) of phosphorus (P), 46 to 734 kg ha−1 of potassium (K), 150 to 7,620 kg ha−1 of calcium (Ca), 26 to 1,090 kg ha−1 of magnesium (Mg), 1 to 190 kg ha−1 of zinc (Zn), 145 to 800 kg ha−1 of estimated sulfur (S) based on organic matter, and 57 to 300 kg ha−1 of sodium (Na). These soil parameters were highly variable among cogongrass populations, even within physiographic regions or land use areas, and encompassed much of the soil physiochemical diversity within the state. Soil characteristics were significantly correlated with leaf length (Ca, K, Mg, P, Zn, and percentage of sand and silt), leaf width (Ca, P, Mg, and percentage of sand and silt), the leaf length-to-width ratio (K and P), inflorescence length (Na, P, and pH), inflorescence width (S, organic matter, and pH), and the inflorescence length-to-width ratio (S and organic matter). These data indicate that cogongrass is able to establish, emerge, grow, and reproduce on a wide array of soils in Mississippi. This ability provides cogongrass an advantage over other plant species that are more limited in the soil types that support their growth. Nomenclature: Cogongrass, Imperata cylindrica (L.) Beauv. IMPCY

Pitted and Hybrid Morningglory Accessions Have Variable Tolerance to Glyphosate

Abstract Two greenhouse studies were conducted to investigate the variability in tolerance to a sublethal dose of glyphosate among accessions of pitted morningglory, hybrid morningglory (a fertile hybrid between pitted and sharppod morningglory), and sharppod morningglory, collected from several states in the southern United States. The first study was conducted to evaluate the variability in tolerance to glyphosate among accessions. Glyphosate at 420 g ae/ha was applied to plants at the four- to five-leaf stage, and control (percent shoot fresh weight reduction) was determined 2 wk after treatment (WAT). Pitted morningglory response ranged from −9% (indicating no response to glyphosate) to 39% control. A similar trend was observed in hybrid morningglory. Control of two related species, cypressvine morningglory and red morningglory, averaged 40 and 29%, respectively, and was similar to control of the most susceptible pitted morningglory and hybrid morningglory accessions. Ivyleaf morningglory control was 9%. Sharppod morningglory control was highest (48%) among the morningglories studied. A second study was conducted to determine levels of tolerance to glyphosate based on GR50 (dose required to cause a 50% reduction in plant growth) in 10 accessions that were least to most sensitive to glyphosate (7 pitted, 2 hybrid, and 1 sharppod morningglory). Glyphosate GR50 doses ranged from 0.65 to 1.23 kg/ha, a two-fold variability in tolerance to glyphosate among the 7 pitted morningglory accessions. Increasing levels of tolerance were associated with the absence of a leaf notch. These results indicate the existence of variable tolerance to a sublethal dose of glyphosate among accessions of pitted morningglory. Nomenclature: Glyphosate; cypressvine morningglory, Ipomoea quamoclit L. IPOQU; hybrid morningglory, Ipomoea × leucantha Jacq.; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; pitted morningglory, Ipomoea lacunosa L. IPOLA; red morningglory, Ipomoea coccinea L. IPOCC; sharppod morningglory, Ipomoea cordatotriloba Dennst. IPOTC;

In-Crop and Autumn-Applied Glyphosate Reduced Purple Nutsedge (Cyperus rotundus) Density in No-Till Glyphosate-Resistant Corn and Soybean

Abstract A 3-yr field study was conducted from 2005 to 2007 at Stoneville, MS, to determine efficacy of in-crop and autumn-applied glyphosate on purple nutsedge density and yield of no-till glyphosate-resistant (GR) corn and GR soybean. Separate experiments were conducted in GR corn and GR soybean in areas maintained under a no-tillage system after the autumn of 2004. Each experiment was conducted in a split-plot arrangement of treatments in a randomized complete-block design with and without autumn application of glyphosate at 1.68 kg ae/ha as main plots and in-crop herbicide application (glyphosate- and nonglyphosate-based programs) as subplots with three replications. In GR corn, glyphosate applied in the autumn reduced purple nutsedge density by 40 to 67% compared with no glyphosate during 3 yr. In GR corn, glyphosate applied in-crop reduced purple nutsedge shoot density by 48% in 2005, 92% in 2006, and 100% in 2007 compared with no herbicide. However, GR corn yields were unaffected by either in-crop or autumn-applied glyphosate. In GR soybean, glyphosate applied in the autumn reduced purple nutsedge shoot density by 64 to 83% compared with no glyphosate during 3 yr. Glyphosate applied in-crop in GR soybean reduced purple nutsedge density by 81% in 2005 and by 100% in 2006 and 2007 compared with no herbicide. GR soybean yields were similar in 2005, but yields were 34 and 18% higher in 2006 and 2007, respectively, with autumn-applied glyphosate compared with no glyphosate. GR soybean yields were higher with glyphosate applied in-crop compared with no herbicide in 2 of 3 yr. These results indicate that purple nutsedge density could be reduced with glyphosate applied in-crop in no-till GR corn and GR soybean. In addition, autumn-applied glyphosate was effective in reducing purple nutsedge populations following harvest of crops and could be an effective purple nutsedge management strategy regardless of GR trait. Nomenclature: Glyphosate; chlorimuron; halosulfuron; S-metolachlor; purple nutsedge, Cyperus rotundus L. CYPRO; corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Preparation and Use of Voucher Specimens for Documenting Research in Weed Science

Voucher specimens and herbarium collections provide the foundation for many aspects of research in the plant sciences. Available for study and verification by contemporary and future workers, voucher specimens promote reproducibility in scientific method because permanent records document identification, distribution, and interspecific and intraspecific variation of species. The utility and importance of voucher specimens and herbarium collections in supporting research in weed science are discussed, and the collection, preparation, documentation, storage, and shipment of voucher specimens are detailed.

Response of selected grass and broadleaf species to cogongrass (Imperata cylindrica) residues

Effects of cogongrass foliage and rhizome plus root residues on germination and shoot and root growth of barnyardgrass, bermudagrass, browntop millet, hemp sesbania, Italian ryegrass, and prickly sida were investigated in greenhouse experiments. Ground residues of dried cogongrass foliage and rhizomes plus roots were mixed separately with sterilized sand to obtain residue concentrations of 0, 0.25, 0.5, 1, 2, 4, and 8%. These residue concentrations were investigated on bermudagrass and Italian ryegrass, and the 8% residue concentrations were also evaluated on hemp sesbania, prickly sida, barnyardgrass, and browntop millet. Foliage and rhizome plus root residues at concentrations as low as 0.25% inhibited seed germination and shoot and root growth of all species except hemp sesbania. Germination of bermudagrass and Italian ryegrass was reduced by as much as 97% and shoot and root growth by as much as 94% at the highest residue concentrations. Rhizome plus root residues reduced germination and shoot and root growth of bermudagrass and Italian ryegrass more than foliage residues. Foliage and rhizome plus root residues reduced germination and shoot and root biomass of prickly sida, barnyardgrass, and browntop millet at similar levels. Results indicate that cogongrass tissue may contain allelochemicals that contribute to its invasiveness and extreme competitiveness. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; bermudagrass, Cynodon dactylon (L.) Pers. # CYNDA; browntop millet, Brachiaria ramosa (L.) Stapf. # PANRA; cogongrass, Imperata cylindrica (L.) Beauv. # IMPCY; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; Italian ryegrass, Lolium multiflorum Lam. # LOLMU; prickly sida, Sida spinosa L. # SIDSP. Additional index words: Allelochemical, allelopathy, germination, growth inhibition, plant residues, root growth, seedling, shoot growth. Abbreviations: DAP, days after planting; DDW, double-distilled water.

Morphological Comparison of Morningglory (Ipomoea and Jacquemontia spp.) Populations from the Southeastern United States

Abstract Morningglories are troublesome weeds in row crops and other agricultural areas throughout the United States. Plants of pitted morningglory, sharppod morningglory, and a fertile “hybrid” between pitted and sharppod morningglory (hybrid morningglory), were compared with cypressvine, ivyleaf, palmleaf, purple moonflower, red, and smallflower morningglories in greenhouse studies at Stoneville, MS. Plants from each of 76 accessions were studied for number of nodes to first internode elongation; stem color and pubescence; leaf area and dry weight of first four full expanded leaves; leaf blade pubescence on abaxial and adaxial surfaces and margins; leaf color, shape, and lobing; petiole length, color, and pubescence; sepal length, color, and pubescence; and corolla color, diameter, and length. Among these morningglories, the most diverse traits were pubescence and flower characteristics. Greatest morphological diversity was among hybrid morningglory accessions because characteristics were intermediate to pitted morningglory and sharppod morningglory accessions. Sharppod morningglory had five nodes to first internode elongation compared to three nodes in pitted and hybrid morningglory. Corolla color was white (90%) or white with faint pink veins (10%) in pitted morningglory, lavender (100%) in sharppod morningglory, and varied from pinkish lavender (45%), lavender (38%), white (12%), to white with pink veins (5%) in hybrid morningglory accessions. Pitted, red, and smallflower morningglory corolla diameters were not only smaller, but less variable in size than cypressvine, hybrid, ivyleaf, palmleaf, purple moonflower, and sharppod morningglories. Corolla diameter and lengths were most variable in sharppod morningglory accessions when compared to other morningglory accessions. The sepal tip shape was broader (broadly acute to obtuse) in palmleaf and sharppod than in hybrid, pitted, or other morningglories (acute to narrowly acute). In future studies, these morphological traits will be compared to determine if any are correlated with glyphosate sensitivity. Nomenclature: Cypressvine morningglory, I. quamoclit L. IPOQU; hybrid morningglory, Ipomoea × leucantha Jacq.; ivyleaf morningglory, I. hederacea (L.) Jacq. IPOHE; palmleaf morningglory, I. wrightii Gray IPOWR; pitted morningglory, I. lacunosa L. IPOLA; purple moonflower, I. turbinata L. CLYMU; red morningglory, I. coccinea L. IPOCC; sharppod morningglory, I. cordatotriloba Dennst. IPOTC; smallflower morningglory, Jacquemontia tamnifolia (L.) Gresb. IAQTA.

Effects of Simulated Rainfall on Disease Development and Weed Control of the Bioherbicidal Fungi Alternaria cassiae and Colletotrichum truncatum

Abstract Alternaria cassiae and Colletotrichum truncatum are bioherbicidal pathogens of sicklepod, and hemp sesbania, respectively. The effects of simulated rainfall followed by 12 h simulated dew application, immediately or delayed by 1 to 4 h, on disease severity and weed control were studied for each pathogen on its weed host under greenhouse conditions. After each simulated rainfall event, treated plants were placed in a dew chamber for 12 h. Regardless of rainfall amount and/or timing, only slight differences occurred on A. cassiae disease severity and sicklepod control (85 to 100% for both parameters). However, when similar tests were imposed on C. truncatum, disease severity and hemp sesbania control were highly variable, ranging from 5 to 100%. Regardless of rainfall amount, disease development and control of hemp sesbania were greatly reduced (60%) when dew application was delayed by only 1 h following inoculation, regardless of rainfall treatment. Rainfall at 1.27 and 2.58 cm had little effect on disease development and control in hemp sesbania, but the effect of transfer time to dew application exhibited a greater role on these parameters. Thus the time between bioherbicide application and dew application was more important for C. truncatum than for A. cassiae. These results indicate that rainfall amounts and the timing of dew application caused differential effects on disease severity and weed control after application of these bioherbicides to their target weeds. Nomenclature: Hemp sesbania [Sesbania exaltata (Rydb.)] ex A.W. Hill sicklepod [Senna obtusifolia (L.) Irwin & Barneby]; Alternaria cassiae Jurair & Khan; Colletotrichum truncatum (Schw.) Andrews and Moore.