Distribution and degradation of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 5, 10, 15, and 20 ppmw in red pine (Pinus resinosa Ait.) seedlings were investigated using 14C-ring-labeled simazine dispersed in agar medium. Simazine readily entered red pine roots and moved rapidly into stem and needles. Accumulation was greatest in roots, next in stems, and least in needles. Significant differences in simazine uptake by roots were observed among concentrations between 5 and 20 ppmw in the incubation medium. Radiochromatographic scans revealed that a small amount of simazine was degraded to three unknown compounds by both fresh and boiled homogenates from whole plants, needles, stems, and roots. There were no observable differences in the amount of simazine degraded by homogenates of each separate plant part.

The relationship between susceptibility of certain plant species to 4,6-dinitro-o-sec-butylphenol (DNBP) and their capacity to accumulate externally supplied P32, and to form ATP in leaf disks was studied. A correlation was found between susceptibility of the species to DNBP and their capacity for P32 accumulation and ATP synthesis. Therefore, it was postulated that susceptibility depends upon the level of ATP in the tissues.

The seed weevil (Microlarinus lareynii Jacquelin duVal) and the stem weevil (M. lypriformis Wollaston) were introduced into the United States and the West Indies to control puncturevine (Tribulus terrestris L.) and Jamaica feverplant (T. cistoides L.). In 14 yr these weevils have partially controlled these weeds in most areas where weevil establishment has occurred. However, indigenous parasitoids, predators, and cold weather affect weevil densities. Presently a coldhardy strain of seed and stem weevils has become established in Nevada and promise control in colder areas.

Downy brome (Bromus tectorum L.) control by 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat) was increased from 12% without surfactant to 73 to 94% with 17 of 22 surfactants. Paraquat toxicity was greatest at 0.06 and 0.12% surfactant concentrations and decreased at higher concentrations. The less effective surfactants were less water-soluble and more lipophilic than related, more effective ones.

Inulin or a closely related analog was the major available carbohydrate component of western ironweed (Vernonia baldwinii Torr.) roots. Fructose, glucose, sucrose and other gluco-fructosans made up the remaining carbohydrate fraction. Reductions in ironweed vigor as a result of annual mowing were caused by a decrease in dry weight of the root system rather than a permanent decrease in carbohydrate percentage. Use of carbohydrate percentage in predicting a physiological condition of ironweed was regarded as questionable. Carbohydrate content of roots was not necessarily related to stage of growth. Treatment of ironweed with 2,4-D did not permanently affect carbohydrate levels in the roots. Changes in root carbohydrate content after 2,4-D treatment were not considered decisive in killing ironweed.

When applied in enough water to wet tubes of dry Pullman silty clay loam top soil to a depth of 22 inches, dimethylamine salts of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) and polychlorobenzoic acid (PBA) were leached to about 20 inches; an amine salt of 2,4-dichlorophenoxyacetic acid (2,4-D) and the sodium salt of 2,3,6-trichlorophenylacetic acid (fenac) leached to 15 inches; esters of fenac, 3-phenyl-1,1-dimethylurea (fenuron), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) and amine salts of 2-(2,4,5-trichlorophenoxyl)propionic acid (silvex) and 2,4,5-trichlorophenoxy-acetic acid (2,4,5-T) leached to approximately 9 inches. Esters of silvex, 2,4,5-T, and 2,4-D remained in the top 3 inches of soil. The leaching with additional water was in the same general order as just given.

Tillage regimes can influence weed population dynamics and, consequently, the choice of appropriate weed management practices. Studies were conducted in 2016 and 2017 in a long-term (36-yr) grain sorghum [Sorghum bicolor (L.) Moench ssp. bicolor] experiment at Texas A&M University, College Station, to determine the impact of long-term no-till (NT) and conventional till (CT) systems on weed species dynamics. Higher densities of johnsongrass [Sorghum halepense (L.) Pers.], prostrate spurge [Chamaesyce humistrata (Engelm. ex A. Gray) Small], waterhemp [Amaranthus tuberculatus (Moq.) Sauer], and henbit (Lamium amplexicaule L.) were recorded in the NT system compared with the CT system. Further, the NT system showed greater weed diversity (Shannon-Wiener index, H = 0.8) and species richness (S = 6.2), compared with the CT system (H = 0.6, S = 4.2). Seedling emergence of some dominant weed species was also delayed in the NT system. In the CT system, 50% emergence of S. halepense (8.5 C base temperature) and waterhemp (10 C base temperature) occurred at 59 and 63 growing degree days (GDD), respectively, whereas 68 and 75 GDD, respectively, were required in the NT system. Further, a greater proportion (61%) of the viable seedbank was present at the top 5 cm of the soil in the NT system compared with the CT system (46%). Overall, findings from this 36-yr-long tillage experiment have revealed that the NT system had greater weed densities (especially of the perennial weed S. halepense) and a high proportion of weed seeds (particularly small-seeded annuals) on the topsoil layer, corroborating some earlier reports that were based on short-term investigations. Findings indicate that growers transitioning to NT systems should be mindful of potential shifts in weed species dominance and develop appropriate management tactics.

Harvest weed seed control (HWSC) is a weed management technique that intercepts and destroys weed seeds before they replenish the soil weed seedbank and can be used to control herbicide-resistant weeds in global cropping systems. Wild radish (Raphanus raphanistrum L.) is a problematic, globally distributed weed species that is considered highly susceptible to HWSC, as it retains much of its seed on the plant during grain harvest. However, previous studies have demonstrated that R. raphanistrum is capable of adapting its life cycle, in particular its flowering time, to allow individuals more time to mature and potentially shed seeds before harvest, thereby evading HWSC interception. This study compared the vegetative growth plus physiological and ecological fitness of an early-flowering R. raphanistrum biotype with an unselected genetically related biotype to determine whether physiological costs of early flowering exist when in competition with wheat (Triticum aestivum L.). Early flowering time adaptation in R. raphanistrum did not change the relative growth rate or competitive ability of R. raphanistrum. However, the height of first flower was reduced in the early flowering time–selected population, indicating that this population would retain more pods below the typical harvest cutting height (15 cm) used in HWSC. The presence of wheat competition (160 to 200 plants m−2) increased flowering height in the early flowering time–selected population, which would likely increase the susceptibility of early-flowering R. raphanistrum plants to HWSC. Overall, early-flowering adaption in R. raphanistrum is a possible strategy to escape being captured by the HWSC; however, increasing crop competition is likely to be an effective strategy to maintain the effectiveness of HWSC.

Leafy spurge (Euphorbia esula L.) is an invasive perennial weed infesting range and recreational lands of North America. Previous research and omics projects with E. esula have helped develop it as a model for studying many aspects of perennial plant development and response to abiotic stress. However, the lack of an assembled genome for E. esula has limited the power of previous transcriptomics studies to identify functional promoter elements and transcription factor binding sites. An assembled genome for E. esula would enhance our understanding of signaling processes controlling plant development and responses to environmental stress and provide a better understanding of genetic factors impacting weediness traits, evolution, and herbicide resistance. A comprehensive transcriptome database would also assist in analyzing future RNA-seq studies and is needed to annotate and assess genomic sequence assemblies. Here, we assembled and annotated 56,234 unigenes from an assembly of 589,235 RNA-seq-derived contigs and a previously published Sanger-sequenced expressed sequence tag collection. The resulting data indicate that we now have sequence for >90% of the expressed E. esula protein-coding genes. We also assembled the gene space of E. esula by using a limited coverage (18X) genomic sequence database. In this study, the programs Velvet and Trinity produced the best gene-space assemblies based on representation of expressed and conserved eukaryotic genes. The results indicate that E. esula contains as much as 23% repetitive sequences, of which 11% are unique. Our sequence data were also sufficient for assembling a full chloroplast and partial mitochondrial genome. Further, marker analysis identified more than 150,000 high-quality variants in our E. esula L-RNA–scaffolded, whole-genome, Trinity-assembled genome. Based on these results, E. esula appears to have limited heterozygosity. This study provides a blueprint for low-cost genomic assemblies in weed species and new resources for identifying conserved and novel promoter regions among coordinately expressed genes of E. esula.

Additional active ingredients are needed for use in aquatic systems to respond to new threats or treatment scenarios, enhance selectivity, reduce use rates, and mitigate the risk of herbicide resistance. Florpyrauxifen-benzyl is a new synthetic auxin developed for use as an aquatic herbicide. A study was conducted at North Carolina State University in which 10 µg L−1 of 25% radiolabeled florpyrauxifen-benzyl was applied to the isolated shoot tissue of 10 different aquatic plant species to elucidate absorption and translocation patterns in these species. Extremely high levels of shoot absorption were observed for all species, and uptake was rapid. Highest shoot absorptions were observed for crested floatingheart [Nymphoides cristata (Roxb.) Kuntze] (A192 = 20 µg g−1), dioecious hydrilla [Hydrilla verticillata (L. f.) Royle] (A192 = 25.3 µg g−1), variable watermilfoil (Myriophyllum heterophyllum Michx.) (A192 = 40.1 µg g−1), and Eurasian watermilfoil (Myriophyllum spicatum L.) (A192 = 25.3 µg g−1). Evidence of translocation was observed in all rooted species tested, with the greatest translocation observed in N. cristata (1.28 µg g−1 at 192 h after treatment). The results of this study add to the growing body of knowledge surrounding the behavior of this newly registered herbicide within aquatic plants.

A quantitative colorimetric procedure was developed for the determination of N-glucosyl amiben in tissue sections of etiolated seedlings. N-glucosyl amiben biosynthesis in soybean hypocotyl sections was heat labile, sensitive to freezing and thawing, unaffected under anaerobic conditions, dependent on amiben concentration, and proportional to tissue section concentration. The formation of N-glucosyl amiben in soybean hypocotyl sections was greatest between pH 6.3 and pH 7.3 and was inhibited by NaF, HgCl2, iodoacetate, iodoacetamide, and N-ethylmaleimide but not by NaCN or NaN3. On a specific activity basis, sugar beet seedling, soybean cotyledon, and soybean hypocotyl tissue sections were the most active tissues studied in the biosynthesis of N-glucosyl amiben.

Hoary alyssum (Berteroa incana (L.) D.C.) was selectively controlled in alfalfa (Medicago sativa L.) by 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 2 lb/A, 3-tert-butyl-5-bromo-6-methyluracil (hereinafter referred to as DuPont 733) at ½ and 1 lb/A, 2,4-dichlorophenoxybutyric acid (2,4-DB) at ½ and 1 lb/A, and by 3-tert-butyl-5-chloro-6-methyluracil (terbacil) at ½ and 1 lb/A. Alfalfa yields were not reduced with consecutive applications for 3 years with the exception that simazine at 2 lb/A caused a significant reduction in first harvest hay yields in the first 2 years. Herbicide applications were made as soon as possible after the last forage harvest in early fall. Treatment at that time destroys the existing photosynthetic area and should reduce the accumulation of carbohydrate reserves in the roots, thereby inhibiting the development of cold hardiness by hoary alyssum plants.

Non-lethal dosages of 2,4-dichlorophenoxyacetic acid (2,4-D), which stunted pigweed plants, markedly reduced transpiration. Lethal dosages of 2,4-D, 2,2-dichloropropionic acid (dalapon), or toxic oil reduced transpiration rapidly, but transpiration continued until treated plants were air dry. Large plants died slower than small plants after herbicide treatment; consequently, they transpired more water before death.

Some seeds of Cicuta douglasii (DC.) Coult. & Rose (western waterhemlock), Cuscuta planiflora Tenore (smallseed dodder), Cuscuta indecora Choisy (largeseed dodder), Linaria dalmatica Mill. (Dalmatian toadflax), Asclepias speciosa Torr. (showy milkweed), and Halogeton glomeratus (M. Bieb.) C. A. Mey (halogeton) (brown seeds) still germinated after 12 months of submergence at 12- and 48-inch depths in canal water. Black seeds of halogeton were not viable after 6 months. In another test, 35 percent of the seeds of Polygonum persicaria L. (ladysthumb) remained firm and 24 percent germinated after 5 years. Seeds of Cichorium intybus L. (chicory) and Swainsona salsula (Pall.) Taub. (swainsonpea) were not decomposed and devitalized in toto until after 5 years. No seeds of Avena fatua L. (wild oat), Bassia hyssopifolia (Pall.) Kuntze (fivehook bassia), and Rumex crispus L. (curly dock) sprouted after 6, 18, and 42 months, respectively. No seeds of Salsola kali L. var. tenuifolia Tausch (Russian thistle) and few seeds of Sonchus arvensis L. (perennial sowthistle) germinated after 3 months.

‘Cargill 921′, ‘Great Lakes 422′, ‘Northrup King 9410′, ‘Pioneer 3901′, ‘Pioneer 3737′, and ‘Stauffer 5650’ corn hybrids were tested in the greenhouse for imazaquin tolerance. Imazaquin rates that reduced shoot growth 50%, when compared to the untreated hybrid check, ranged from 17 to 50 g/ha. When averaged together, the three most tolerant hybrids (Cargill 921, Pioneer 3901, and Great Lakes 422) were approximately one-half as sensitive to imazaquin as the three least tolerant hybrids (Northrup King 9410, Pioneer 3737, and Stauffer 5650). Studies were conducted to determine if the observed differential tolerance was caused by differences in acetolactate synthase (ALS, EC 4.1.3.18) levels and sensitivity of ALS to imazaquin. Differential imazaquin uptake, translocation, and/or metabolism were also studied as a basis for the tolerance range as was seed size and seedling growth. There were differences among hybrids in the physiological and growth parameters studied; however, these differences did not correlate with imazaquin tolerance. None of the factors studied could alone account for the differences in imazaquin tolerance.

Field studies were conducted to measure the response of corn (Zea mays L. var. ‘Pioneer 3377’) to foliar applications of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} as influenced by corn growth stage and the addition of 7.7, 15,4, 77.7, 140, 280, and 840 g/ai/ha of bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Applications of sethoxydim (16.8, 33.6, 67.2, 100, and 134 g ai/ha), fluazifop, or haloxyfop (1.0, 2.0, 4.0, 8.0, 10.0, and 13.4 g ai/ha) to four- to five-leaf corn did not reduce seed weight, but significant reductions resulted when sethoxydim (100 g/ha) or fluazifop (13.4 g/ha) was applied to 70- to 80-cm (six-leaf) corn with or without bentazon. Corn grain yield was significantly reduced by sethoxydim (>67.2 g/ha) treatment at either growth stage of corn. In contrast, corn injury induced by fluazifop (>8.0 g/ha) and haloxyfop (13.4 g/ha) resulted in reductions in yield only when applications were made to 70- to 80-cm corn. Significant reductions in seed germination also resulted from foliar applications of the graminicides, but these reductions were inconsistent across corn growth stage.

Laboratory and greenhouse studies were conducted to determine the effect of temperature, solution pH, water stress, and planting depth on cutleaf eveningprimrose germination and emergence. Field studies were conducted to measure growth parameters of cutleaf eveningprimrose throughout the fall season. When treated with constant temperature, cutleaf eveningprimrose germinated over a range of 15 to 32 C, with the optimum germination occurring at 24 C. Onset, rate, and total germination were greatest in an alternating 20/35 C temperature regime. Germination decreased as solution pH increased, with greatest germination occurring at solution pH of 4. Germination decreased when cutleaf eveningprimrose seed was subjected to increased water stress. Emergence was optimum when seed were buried at depths of 0.5 cm. Germination decreased with increasing burial depth, and no seed emerged from a depth of 10 cm. Cutleaf eveningprimrose control was maximized when 2,4-D was applied in mixture with glyphosate or paraquat. These data suggest that cutleaf eveningprimrose can germinate and gain biomass from early March to late October. These attributes could contribute to poor control before cotton planting if preplant control applications are delayed after early March.

EPTC (S-ethyl dipropylthiocarbamate) was applied to seed of alfalfa (Medicago sativa L.) that was coated with a porous material consisting principally of lime or gypsum. When the treated seed was planted in the field or greenhouse, grass was controlled selectively. When seeds, each carrying 0.1 mg EPTC, were seeded 1 cm apart in rows, the rate of EPTC would have been 2 kg/ha if this quantity of EPTC had been distributed in a band 5 cm wide. Such applications controlled grass completely in bands 5 to 6 cm wide. When seeds, each carrying 0.2 mg EPTC, were evenly distributed at seeding rates of 14 or 25 kg/ha, the broadcast rates of EPTC were 1.3 and 2.2 kg/ha. Both rates controlled grass completely. Storing EPTC-treated seed for 1 yr at 5 C did not affect germination of the seed or emergence and growth of the seedlings.

Field experiments were established in 1989 and 1990 at the Southern Piedmont Conservation Research Center near Watkinsville, GA, to determine effects of coastal bermudagrass density on cotton in a conservation tillage system. Cotton height, canopy width, leaf area indices, and seed cotton yields were determined at coastal bermudagrass densities of 0 to 3600 kg ha−1 as achieved by herbicide inputs. Soil water measurements were recorded in cotton plots with a range of coastal bermudagrass densities using time domain reflectometry. Cotton growth and yields were reduced by coastal bermudagrass competition both years of the study. At the highest coastal bermudagrass density of 3600 kg ha−1, cotton height was reduced compared to cotton alone as early as 5 wk after planting. Seed cotton yields were reduced 25% at the highest coastal bermudagrass densities both years of the study. At the 15-cm soil depth, coastal bermudagrass significantly reduced soil water in cotton. Soil water in cotton at 30, 45, and 60 cm was not affected by coastal bermudagrass.

In greenhouse and field studies, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} controlled quackgrass [Agropyron repens (Beauv.) # AGRRE] in potato (Solanum tuberosum L. ‘Russet Burbank’). Quackgrass control with fluazifop at 0.25 and 0.5 kg ai/ha in the greenhouse was greatest with application at the two-leaf stage compared with the four-and six-leaf stages. Control was not affected by rhizome length, with similar control obtained of plants grown from 2- and 10-node rhizome pieces. Removal of quackgrass shoots at 6 or 24 h after treatment resulted in decreased control at application rates of 0.25 and 0.5 kg/ha. Fluazifop at 0.5 kg/ha controlled quackgrass treated at the four-leaf stage. The active enantiomer of fluazifop at half the rate of the racemic mixture controlled the quackgrass to the same extent. Fluazifop did not affect potato yield.